Exploring the Galaxy View RSS

Lock Free - Part Deux 13 Jul 2013 12:22 AM (11 years ago)

It's been a while since my last post and I've spent the last year working on lots of cool stuff at Valve. I worked on the item importer for Team Fortress 2, helped with the Linux Steam launch, and am currently working on very cool unannounced tech, which I'm looking forward to sharing with people soon.

In the meantime, I'm lucky enough to be sitting across from Bruce Dawson, who is one of the most amazing people I know when it comes to crash analysis, performance analysis, and "what the heck is my system doing?"  His blog is full of all sorts of interesting things, and you can check it out at http://randomascii.wordpress.com/ It also turns out that he was the author of the GDC talk that I saw a few years ago which got me interested (and afraid of) lockless programming. It's a small world! :)

So occasionally I like to break out of what I'm doing day to day and catch up on SDL work, which always has different and interesting challenges.

This week I went and fixed a bug in SDL regarding OpenGL context caching. An OpenGL context is made "current" on a given thread, and each thread can have a different context active. SDL was caching the current context in a global variable, which is completely wrong.  What I really needed here was thread-local storage.

No problem, I'll just add it to SDL!

It turns out that each supported OS has the concept of thread-local storage, and all I need is a single slot of OS thread-local storage to implement a full set of SDL based thread-local storage. However, by its very nature, multiple threads may allocate from it simultaneously and I needed an efficient way to make sure only a single thread allocates the first OS slot.

No problem, SDL already has spinlocks which are a good candidate for quick initialization like this:

static DWORD thread_local_storage = TLS_OUT_OF_INDEXES;

SDL_TLSData *
SDL_SYS_GetTLSData()
{
    if (thread_local_storage == TLS_OUT_OF_INDEXES) {
        static SDL_SpinLock lock;
        SDL_AtomicLock(&lock);
        if (thread_local_storage == TLS_OUT_OF_INDEXES) {
            thread_local_storage = TlsAlloc();
        }
        SDL_AtomicUnlock(&lock);
    }
    return (SDL_TLSData *)TlsGetValue(thread_local_storage);
}

I had Bruce come over and look at it since I knew he was well versed in this sort of thing, and he pointed out that even though I'm using a lock, it's really a form of lockless programming since I don't unconditionally acquire a lock before testing state.

I thought I was pretty safe, since I was double checking the condition after acquiring a lock, so if multiple threads tried to acquire the lock simultaneously only one would actually do the initialization. The assignment is an atomic operation, so if another thread passed the if conditional it would have a valid value in thread_local_storage and would be fine.

Bruce pointed out that at the machine level it's a giant soup of memory and instructions, and memory accesses inside TlsAlloc() may be reordered relative to the assignment of the return value.  As compilers get better at inlining during link time optimization, there may not even be a function call and return value. This is a common problem with the double-checked locking that I'm doing here.

What I really want to do is guarantee that all data initialization involving TlsAlloc() are written to memory before any the write to thread_local_storage ‘publishes’ them. And conversely, I want any other thread to be sure it can see all the data associated with thread_local_storage before it starts using it.

The right tool here is memory barriers. On x86 and x64 architectures memory barriers are simply instructions that prevent the compiler from reordering CPU instructions, since the hardware is strongly ordered (other CPUs see writes in the order they occur.) On ARM and PowerPC CPUs memory barriers are hardware instructions that force synchronization. Jeff Preshing has a great blog that explains how to think about them, along with lots of other great information about lockless programming:
http://preshing.com/20120913/acquire-and-release-semantics

Essentially, the initializing thread performs a bunch of work, then sets a flag variable and issues a write-release. All other threads check the flag variable, perform a read-acquire, and then continue using the data signaled ready by the flag.

Applying this here, we end up with:

static DWORD thread_local_storage = TLS_OUT_OF_INDEXES;

SDL_TLSData *
SDL_SYS_GetTLSData()
{
    if (thread_local_storage == TLS_OUT_OF_INDEXES) {
        static SDL_SpinLock lock;
        SDL_AtomicLock(&lock);
        if (thread_local_storage == TLS_OUT_OF_INDEXES) {
            DWORD storage = TlsAlloc();
            SDL_MemoryBarrierRelease();
            thread_local_storage = storage;
        }
        SDL_AtomicUnlock(&lock);
    }
    SDL_MemoryBarrierAcquire();
    return (SDL_TLSData *)TlsGetValue(thread_local_storage);
}

It's tempting to simply add the word "volatile" to the declaration of thread_local_storage, but that's not exactly what we want. Visual Studio has implemented volatile as having the correct memory barrier semantics when using /volatile:ms, but other compilers simply guarantee that the they won't reorder reads and writes around it, and the CPU is completely free to ignore that. In fact, it may be safer to define a new keyword that indicates that multiple threads access a variable but doesn't have volatile semantics, and always use memory barriers when appropriate.

The final code in SDL has error handling and a fallback to a slower generic implementation in case the process is out of thread-local storage slots, but I believe this is a correct and complete example of thread-safe initialization.

Cheers!

Work/Life Balance in the Games Industry 2 Jun 2012 6:19 PM (12 years ago)

I've been thinking a lot about what's most important to me in new opportunities...

I want to learn new skills, be a part of a talented and healthy team, and work on great things in the games industry. But as I realized a year ago, a huge priority for me is also to have a happy home life along with my professional life.

Work Life Balance

These words are tossed about to the point of buzzword cliché, but what they really boil down to is finding ways to have a happy, healthy, sustainable, efficient work and home life.

There are horror stories in the industry about people working themselves to the bone, crunching for months and sometimes towards an ever receding horizon of a project ship date, destroying their families in the process.  This was viewed as acceptable by big publishers because the title would ship, everybody would crash, take a few months to recover, and sometimes be laid off or move on to the next project and start the cycle all over again.

I think everyone agrees at this point that it's a terrible model for development.  As companies are starting to switch to a service model, they can't release a product and then have the development staff crash.  You can't have people burn out and leave the project, because it's when the title ships that the work really begins.

So what continues to drive the desire for overtime?  From a high level management perspective, the hours an employee works are the only knob they have to turn to increase production output.  And for short periods, this really works.  Need to get 6 weeks of work done to meet a deadline in a month?  Have everybody work 12-14 hours a day.  Production is increased, the deadline is met, success!

The problem of course is that this is not sustainable, and there is always a drop off in efficiency over time and a recovery period necessary.  Different people have different levels of productivity increase from overtime, and the productivity drop and recovery time vary significantly based on age, stress and other life factors, but the general pattern is the same:




In the world of game development engineering, the productivity drop off can be much steeper, because tired people tend to take longer to solve problems, solve them in non-optimal ways, and often introduce bugs that cause wasted time in the Q/A and bug fixing process.

Quality of Work

The first part of good work life balance is having a healthy work environment without extended overtime. But in today's world of rapid iteration and/or constantly increasing game features and scope, how do we achieve this?

• Good planning and scoping
• Good time estimations
• Good communication
• Improving efficiency
• Stop working

Good time estimation and frequent review of progress are crucial to good planning and scoping.  It's important to factor in time for iteration on customer experience and bug fixing into the overall schedule. When I'm estimating time, I usually estimate how long I think a feature or task will take to implement, then I triple it.  This usually gets pretty close to the actual total time cost, including handling unforeseen issues, making required improvements and bug fixing.

Good communication with management leads to trust on both sides (hopefully!) and helps reduce stress in the workplace. Good communication with production staff helps tighten the planning feedback loop and makes sure that re-scoping happens early enough so that teams can account for it and minimize wasted work.  Good communication among engineering staff is really helpful to share key information or smart ideas to accelerate work, or even make it unnecessary.

For example, when I was leading the social systems Battle.net team, I noticed that some people new to the team (including me) were spending a lot of time digging through code, or struggling finding the right way to solve problems in the codebase. So one of the things I implemented was a rule that before starting a task or trying to fix a bug, the person should stand up in our area and mention they were working on it and ask if anyone had any advice.  This didn't affect the old hands much, since they held most of the knowledge already, but new people achieved about a threefold improvement in efficiency and very quickly ramped up on the systems and history of design decisions.  We also caught some cases where new designers were making requests that conflicted with previous design decisions and saved ourselves work that would have been thrown away.

Improving efficiency so a team can get more work done more effectively is always a good idea. Work done improving Q/A processes means better morale, better bug flow, and better interaction between Q/A and engineering. Work done to reduce iteration times, build times, export times, game startup time, etc. repays itself in spades. Experienced engineers multi-task so while waiting for things they're thinking about the next problem, or reviewing the code for correctness, etc., but there's always some time wasted in context switching, so reducing waiting time is almost always good.

The flip side of course, is that if everything is too efficient, it's easy to forget to take breaks and slowly become fatigued, which leads me to my next point...

Stop working!

If I am sitting there trying to figure out a problem and it's taking a while, the best thing for me to do is to get up, walk around and do something else. I'll often come up with the solution while away, or when I come back to the code I'll have a fresh perspective and get the solution quickly.

Solving more challenging problems are always easier for me if I go home, spend time with my family, and have a good long shower in the morning.

Both at Blizzard and 38 Studios I was a part of a hack circle that met mid afternoon, and invariably I would be much more productive after I got up and got the blood flowing, and the adrenaline pumping.

A friend of mine who led a team at Sony once told me that when his engineers came to him with a problem, he would tell them to go talk to a tree.  He wasn't being flippant - getting out and talking through the problem in the sunshine near a convenient source of elevated oxygen actually improves brain activity and helps solve problems.

Quality of Life

The second part of good work life balance is of course, life.  We are social animals and we need friends and good relationships, good food, fun and exercise to be at our best.

For me, having a happy home life is extremely important to how well I do at work. If my wife isn't happy, ain't nobody happy, and I can't really concentrate and be effective on the job. If I get smiles and hugs from my kids in the morning I have smiles for the rest of the day.

Coping with Crunch

So the planning failed, you have to work overtime to get the product ready for a milestone and production and management are willing to accept the costs. What do you do to stay healthy, happy, and efficient?

The first thing to do is know your priorities.  Make sure that you're reaching for specific goals instead of just adding more time to the stack.  Find ways to work smarter so that you're doing exactly what needs to be done to achieve those goals.  Don't need that afternoon meeting? Ditch it! Wasting time context switching with various tasks? Mark off blocks of time that are devoted to certain types of work. Some of these kinds of things are good to do anyway to improve your work processes, and some are temporary measures to let you stay super focused.  You might find that getting hyper-focused is all you need to get the work done without any overtime at all.

The second thing is to stay flexible and know your limits. Don't just work exactly 12 hours because someone mandated it. Some days you'll be more tired and need to stop early. Other days you'll be on a roll and want to finish something up for another few hours.  Remember to take your breaks to stay working efficiently and able to focus. If you need to stop, be honest with yourself and your team. It doesn't do anyone any good to make tired decisions and write poor code that will cost everyone later.

Be creative and find ways to make things work best for you. Don't neglect the important things in life even if it feels like work is temporarily more urgent. If you only have one evening available, maybe make it a date night. If you're missing meals with the family, maybe they can join you for lunch, or maybe you can swing your hours early or late so you get breakfast or dinner with them. You might want to get out of the office on breaks for a change of scenery and a chance to decompress. Take some friends and go running to blow off steam...

Be patient. Extended overtime is hard on you, your family and your team, and a good attitude goes a long way to making it easier for everyone.

Conclusion

Having a healthy balanced life is a big priority for me, and luckily a lot of companies know the importance of work life balance and are working to create a good sustainable environment for their employees. I'm excited to meet more of them over the next few weeks.

38 Studios Coda 2 Jun 2012 1:41 PM (12 years ago)

So I haven't blogged in the past year, since I was busy at 38 Studios and much of what I was working on was confidential.  Suffice it to say that it was indeed my dream job. Working with good friends on an amazing project with the full support of the company and a great work/life balance.

Lots of people have talked about what happened at the company, so I'll just give the short and sweet version...
The company ran out of money, and instead of spending the last of it gracefully shutting down, they prayed for a miracle that never happened. Yes, I believe the governor's press statements didn't help, but the company was so close to zero that an extra month of operation may not have been enough. The story is tragic, and gets more so each week as more details come to light.

But, I am thankful for one of the best game development years of my life, and I am amazed and happy at how we, our friends, and the industry as a whole have been so supportive.  We intended to change the world with our game, but we are changing the world through our shared bond and the knowledge of what we had, what we did, and what can be.  I feel like I have a family that will last for the rest of our lives, spreading throughout the industry and beyond.

Thank you!

38 Studios 15 May 2011 6:10 PM (13 years ago)

So once I decided not to start my own company, I started looking around for a company in the games industry that really had employees, and more importantly, employees' families at the forefront of their priorities. I wanted a place I could raise kids, have a life, and make great games with my friends.

38 Studios stands head and shoulders above every other company in the industry in this respect. 38 Studios was founded by Curt Schilling, former Red Sox pitcher, and his passion is building teams. He knows that to create a great game you have to have great people, and treat them and their families well.

Curt will move heaven and earth for his family, and if you're on his team, you're family. Rarely have I met anyone as genuinely passionate and good hearted as he is. He has strong opinions, but he is also wise enough to trust his team and value their opinions and expertise.

When I came to visit I was very impressed by everyone I met. They are smart, nice, and honest with themselves and each other. They realize they have a tremendous task in front of them, creating a company, creating a great game, creating a world. But each time I've seen them approach a problem, I've seen them solve it in innovative and great ways. Each time I've seen them choose between the expedient path and what's right for the team, they've done what's right for the team. Not only does that hold true at the top levels, but that attitude, flexibility and self-empowerment is there in everyone I talk to.

38 Studios faces challenges, for sure. They are trying to do something that hasn't been done before. They are a privately owned company making an MMO, and trying to do it in a healthy sustainable way. They are growing quickly and trying to prepare themselves for the transition to a service organization while at the same time creating a quality content game. They are trying to find the right formula and the right people and they're trying to do it in a realistic time frame.

Can they do it? I don't know. But I am incredibly motivated to help them try, because if they can pull this off, this is my dream come true. A great company, great people, and a quality life for my family and me.

My first day starts tomorrow. Wish me luck! :)

Exploring the Galaxy 6 Apr 2011 5:34 PM (14 years ago)

In 2008 I created Galaxy Gameworks as a small LLC to handle commercial licensing of Simple DirectMedia Layer on the iPhone. Since then I have been maintaining it at a minimal level in my spare time to make it possible for people to use SDL on iOS and other embedded platforms.

As soon as I made the concrete decision to leave Blizzard, my brain started exploding with ideas on how to expand Galaxy Gameworks into a full blown games middleware company. My vision was to build the company into three pillars each designed to help people make games:

1. Software: Starting with SDL and expanding to meet important needs for small developers, based on my experience leading a development team at Blizzard Entertainment.
2. Education: I have always been a big fan of student and indie development, and I know an awesome woman, Brandii Grace, who used to teach at Digipen and is on the board of the LA Independent Game Developer Association who could help start this.
3. Consulting: This is a less developed idea, but there are lots of companies that need help at strategic points to help get their games shipped, and this would be a great service to complement software and education.

As soon as I left Blizzard, I blasted into overtime starting development on SDL and learning what I needed to build Galaxy Gameworks into a real business. I had lots of connections and people interested in what I was doing, and was really excited about the possibilities. I gave myself until the end of March to explore what is involved with creating a company and making my dream a reality, without committing myself.

It was a really amazing experience. I brought all the pieces together to start the company:

Company Vision
I have seen quite a few companies in my day, and I wanted to bring a company vision that incorporated the best of what I have seen, with an eye towards practicality and treating employees really well. I also wanted to have clear goals so that employees who are brought on and potentially given ownership have a good idea of the kind of company we are trying to make.

Virtual Office
I decided early on that I wanted to create a virtual office. This gives flexibility in hiring and reduces overhead, but means you have to work harder to find people who can be self-disciplined, stay motivated, and communicate well remotely. I put together a virtual office around Google services, and set up business phone and FAX. I also worked out the advantages and risks associated with distributed development, and talked to some companies that actually operate that way to find out how it works in practice.

Website
Good branding and easy to use website are really important. Some of the important elements are a showcase for your products, good documentation, clean presentation, and easy navigation.  I hired someone to create a logo (the process is described in another blog post) and create a new website for a commercial presentation.  The result is at http://www.galaxygameworks.com and while it's not complete, it's a good start.

Customer Service
I hired a friend of mine, Jen, to handle customer communication and start setting up hiring processes. She is is amazing at organization and has customer service and HR experience. She is handling the mailing list and forum, organizing bug reports, and handling customer inquiries and licensing. She also did research on the tax implications of hiring contractors and full time employees in other states and potentially other countries.

Documentation
I have been working very closely with my friend Sheena, who has great technical writing skills and is learning programming, to put together high quality API documentation (work in progress at http://wiki.libsdl.org) We also put together plans for tutorials and use cases with examples.

Business Plan
I worked with my wife Lauren and an old friend Jeremy on the draft of a business plan. Lauren is awesome because she is a technical writer by trade and can take large amounts of technical information and organize it in an easy to understand manner. Jeremy is awesome because he's spent the last 15 years or so in software sales and business development, and is extremely innovative and works well with customers.

Between the three of us, we came up with a great business plan centered around three products. The business plan really helped us focus on our goals and business strategy. We thought about our strengths and weaknesses (SWOT analysis), our competitors and potential partners, the trends in the games industry, and our costs and potential sources of income.

We got great feedback on our plan, and a few themes came up repeatedly:

• What problems are you solving?
• Keep it short - what's your elevator pitch?
• Can you show a fast return on investment?

In response to the feedback, we cut one of the products to stay focused and reduce costs and ended up with a revenue and expense chart that looks something like this:


Investors like to see an exponential chart, and a return in the 6-18 month timeframe. :)

Coda
I'm pretty confident I could find some investors at the $300,000 price point and create a small sustainable company creating middleware in the games industry.

At the end of the day though, I realized that even though I have all the pieces I need and lots of support from friends and customers, it was taking all my waking hours and would continue to do so. In a few years when the girls are older and becoming independent that might be okay, but my time with them is precious and I want to have as much of it as possible now.

So, I'm closing Galaxy Gameworks for now, and the quest continues...

How I left Blizzard 4 Apr 2011 3:29 PM (14 years ago)

Blizzard doesn't tend to be very open about how and why people move around at the company, and I still have people asking me what happened, so for those interested I thought I'd share my story.

As far as I know, nothing I'm writing here is confidential, so please tell me if that's not the case.

To understand something of the story, I really should start at the beginning...

After the Wrath of the Lich King launch, I was looking to move on to something new. I loved Blizzard and I didn't want to leave the company, but I wanted to work on a smaller team, a smaller project, with more responsibility. Unexpectedly, a job opened up for technical lead on a small unannounced project that was getting underway. It was a small project, with a short timeframe, at least for Blizzard, and it was a project that I personally was very interested in. I applied, and at the beginning of 2009 I was the engineering lead on a new unannounced Blizzard game!

I was very excited, and spent the first few months researching engine technology, getting some of the  infrastructure set up, and worked with the producer on a detailed technical plan for the project.  After that, since the designers had a solid idea for the game and were making great progress in the prototype, I started work on proving out the gameplay systems and hiring the most urgent engineering positions.

Come July 2009, the company sounded a call to arms to help Battle.net get ready for the Starcraft II launch. There was much to do and each team loaned a person or two to help out. Since our team was so small, most of us went to help out, including our producer and UI artist. We kept a small crew of designers, an artist and our newly hired graphics engineer to keep the project alive during our tour of duty on Battle.net.

We kicked butt, took names, and Starcraft II launched smoothly a year later with Battle.net 2.0.

During the course of that year, our producer was promoted to lead Battle.net producer, and the designers made great strides in evolving the game design and the gameplay model. The graphics engineer had completed the core of the graphics engine and was roughing out the tools pipeline and content creation system.

When we returned from Battle.net, I jumped right on getting our AI/gameplay engineer up to speed on the gameplay systems and started the herculean task of migrating code I had already finished over to the new gameplay model and tools systems that were developed while we were gone.

Three months later that work was being wrapped up, and I was called in to a meeting and told that there were issues on the team.  I had just worked out some issues with my gameplay engineer, but there were issues beyond that, which they needed to follow up on to give me concrete feedback.

Over the next week I implemented a great suggestion from them which improved my communication, our part-time producer led technology goal and milestone meetings which I had requested and were very helpful, I worked on a clear division of labor and responsibility among the team, and I had one-on-one meetings with all of my engineers to see how things were going.  As far as I could tell morale was improved, things were going great with my gameplay engineer, and we had a clear plan for the future.

I was feeling great, and was told that even though things had improved, there were still unspecified issues that were being looked into.  The meeting was very uncomfortable as though something were being danced around, so I mentioned that if the leadership of the team thought it was best, I was willing to step down.  The meeting suddenly relaxed and I got nervous.

A few days later, I was asked to interview someone for technical leadership of the team!  I asked for the chance to talk to whoever was having problems, and was told that would be awkward.  A few days after that it was confirmed that they had already made the decision to have me step down, but that the team leadership was there to help me succeed however they could.

So after a little primal scream therapy, I sat down and really thought about what went right, what went wrong, and what really was important to me.

One of the factors that I think contributed was that we hired really experienced people in the industry, and I hadn't had experience building a small game from the ground up.  Instead of mandating how things should be done, or bringing a set of best practices, I tried to work collaboratively to help us develop the best tools and approaches for our unique needs.  I think this was a creative and good way for us to go given our talents, but I think it increased stress and was possibly interpreted as weakness on a team already feeling time pressure.

So, assuming that was a factor, and since I honestly did not know how other game companies work, I set out on a quest to tour the industry and learn as much as I could about how companies other than Blizzard operate.  I was interested in everything including technology, development processes, team composition, project planning, and business relationships.

I want to stop here and thank everyone who helped me in this quest.  Lots of companies opened their doors and under NDA showed me everything that I wanted to learn about.  Blizzard management too, went way above and beyond the call of duty and introduced me to people who could help me learn about the industry.  I learned that there are a ton of great companies out there, and lots of good ways to approach things.  Thank you all! <3 :)

Armed with a good perspective on the industry and how games are developed, I looked back over how we set up our project and came to the conclusion that it was entirely reasonable, from a tech perspective, and felt comforted.

With that awesome tour completed, I turned my attention back to my future.  My options were to stay on the team as an engineer, transition to another team at Blizzard, leave and start my own venture, or join another company in the industry.

I realized I didn't really want to stay on my team, because even though I love the team and I still think it's an awesome project, I didn't feel like I got any support in that role from management, and I never was told why I was asked to step down.  I don't feel like it was personal, that the management really was trying to do the right thing for the team, but I still didn't want to stay in that environment.

I thought a lot about joining another team at Blizzard, or joining another company, but I realized that after launching Wrath of the Lich King, booting engineering on a new team, and shipping new Battle.net on StarCraft II, all in less than two years, I was starting to feel burned out.  I also looked at myself and realized that sometime in the last ten years I had become a family man, and what I wanted to do more than anything else in the world was spend time with my family.

I took a deep breath and relaxed, feeling my shoulders unclench and my face break out in a smile, and knew I had made the right decision.

Life and Love 11 Mar 2011 10:45 PM (14 years ago)

Every once in a while you see something that takes you completely out of your day to day routine and reminds you that this world is a wide and wonderful place.

Spider Robinson is one of my all time favorite authors, and he has been entertaining me and teaching me about love and laughter most of my life.  I finished the Callahan series (again) tonight, and was touched by the plight of Doc Webster, who passed on with a brain tumor in the final story.  I finally noticed in the back of the book contact information for the American Brain Tumor Association:
http://www.abta.org/

I got on the 'Net and found his website and found that his wife had passed on, in peace, almost a year ago and was able to piece together a little of what his world has been like since then.  He is a brave man with a wonderful family. I'm lucky that I haven't had to deal with the death of someone close to me yet, but this world is richly textured, and people deal with pain and loss and anger and joy and triumph every single day around the world.


If you haven't seen his work, you can check it out in traditional and audio form here:
http://www.spiderrobinson.com/works.html

To all of you who are dealing with and have dealt with loss, I wish you the best, and while I know nothing can ever replace those you've loved, there are still more out there who have loved you, love you now, and will bring you joy in the future.

*HUG*
--Sam

SDL Job Opportunity! 11 Mar 2011 4:42 PM (14 years ago)

Software Engineer - Focus: SDL

• Passionate about helping people make games
• Able and motivated to learn quickly
• Organized
• Good at communicating, both with developers and with customers
• Comfortable with game development concepts
• Comfortable with software design and implementation concepts
• Comfortable using and developing for multiple platforms
• Fluent in C, with a familiarity with some other languages

GDC 2011 7 Mar 2011 2:46 PM (14 years ago)

GDC was really great this year.  It was interesting watching the interplay between different companies and people, and the ebb and flow throughout the show.  I got some great feedback on the business plan, got to pal around the show with an old friend of mine from high school, and learned a lot about presentation.  (note to self: Comic Sans is a terrible font for professional presentation) :)

Aside from the great contacts and fun meeting people, the highlights of the show for me were the exciting things happening on the Indie scene.  Unity had a great booth overflowing with people the whole time, GameSpy announced their Indie technology program, and it seems like every major technology developer has free or extremely inexpensive licensing for independent developers.

Of course each year I really enjoy the Independent Games Festival finalists.  The booth was packed the whole show, so I didn't get to try everything, but there were a few that really stood out in my mind:

Solace - http://solacegame.com
Solace is a blend between top down arcade shooter action and the creative experience of emotion and sound.  I've never seen anything quite like it before, it's definitely worth checking out.

Helsing's Fire - http://www.ratloop.com/?games/helsings_fire
Helsing's Fire has a unique art style and interesting gameplay.  I haven't played all the way through it, but it uses the tried and true method of introducing new elements as the game progresses, so the gameplay is constantly evolving.

Oh, before I forget... I met the developers of Angry Birds!  Wooo! :)

I have lots of followup e-mails to send, so I'm heading out, but until next time... Cheers! :)

Business Phone and FAX 25 Feb 2011 4:58 PM (14 years ago)

For business purposes I need a contact phone and FAX number, but I don't want to have the cost and equipment requirements of a separate phone line.  Given that I'm creating a virtual office, I figured there must be inexpensive and flexible ways of setting up a business phone system.

Google to the rescue, again!

Actually there are lots and lots of options available with different pricing schemes and features, but given that I'm using Google for business e-mail and document sharing, and Google Voice is free, it's a natural fit:
http://www.google.com/voice

It's a little awkward to call from - it requires you to enter the number you want to call and which phone you want to call from and then it calls both and connects the two, but it's freakin' awesome as an incoming voice message system.  You can route your virtual number to any phone you want, and if it goes to voice-mail, Google will take a message, transcribe it to text, and send the message to you via SMS and e-mail.

So, now that voice is taken care of, I need a solution for FAX. Again, there are lots of options available, but given that I plan to use e-mail for most outbound communication and FAX only for receiving signed license documents, OneSuite turns out to be a good option:
http://www.onesuite.com/

You have to create an account and "charge" it with $10, but once you do that, you can activate a FAX number for unlimited incoming transmissions for $1/month.  If you want outgoing FAX capability, or want the incoming FAX messages to go to multiple e-mail addresses, you can upgrade to $2.95/month + 2.5c/page for outgoing transmissions.

Business phone and FAX solution implemented.  Total cost?  $1/month.  Pure win?  Priceless.

Problem Solving in PowerPC Assembly 25 Feb 2011 7:49 AM (14 years ago)

When you're working with other people's code, you don't always have the source, and sometimes this means you have to dive into the assembly code to figure out what's going on.

If you're lucky, there will be a small function where there are well defined inputs and outputs and you can see what's going on...

In this case someone reported a bug where if they created two different streaming textures, the program would crash deep inside glTexSubImage2D() in a routine called gleCopy().  They helpfully sent a small test program, and sure enough, it crashed on my iMac.

So, not having any leads, I start stepping through the assembly code:

...
0x0424a3fc <gleCopy+88>:        mtctr   r4
0x0424a400 <gleCopy+92>:        rlwinm  r0,r9,2,0,29
0x0424a404 <gleCopy+96>:        addi    r9,r9,1
0x0424a408 <gleCopy+100>:       lwzx    r2,r11,r0
0x0424a40c <gleCopy+104>:       stwx    r2,r3,r0
0x0424a410 <gleCopy+108>:       bdnz+   0x424a400 <gleCopy+92>
...
0x0424a464 <gleCopy+192>:       add     r11,r11,r7
0x0424a46c <gleCopy+200>:       add     r3,r3,r8
... 

This is a tight copy loop, where the loop count is loaded from register r4, and the data is copied by offset from pointer r11 and stored at that same offset in poiner r3. At the end of the loop, r11 is incremented by r7 and r3 is incremented by r8.

In C this might look like:

while (rows_to_copy) {
    for (i = 0; i < count; ++i) {
        dst[i] = src[i];
    }
    src += src_pitch;
    dst += dst_pitch;
}

When I printed out the registers, I noticed an interesting thing. The source and destination pointers started out the same, but the source and destination pitches were completely different!

To understand why the source and destination pointers were the same, I looked at the code that creates streaming textures and saw I'm using an Apple extension to have OpenGL use application memory instead of internally allocated memory.  Since I use that same pointer when updating the streaming textures, it makes sense that if the system thought copying needed to be done, it would copy from the pointer I passed in, to the pointer I told it to use for data storage.

But why would it think it needed to do copying?  I looked on the original web page describing how to optimize Mac OS X texture upload and noticed that it had a note saying that only textures with a width of a multiple of 32 bytes would bypass the copying step.  I figured that it shouldn't crash if they didn't have an aligned width, but what the heck.  I resized the textures and as expected the program still crashed.

So what would cause the pitches to be different?  Well, in a normal texture upload, the pitch is controlled by the  GL_UNPACK_ROW_LENGTH attribute.  In a flash, I realized that's probably what the extension uses to determine the original pitch of the texture.  Sure enough, I was missing a call to set that attribute when creating the texture. Looking more closely at the values in assembly, the pitch that it was using for the destination was indeed the pitch value that was set for the first texture upload, and of course if pitch values don't match in a pixel copy operation, you have to copy them row by row, just like the assembly code above was doing.

Adding a call to set GL_UNPACK_ROW_LENGTH in texture creation fixed the problems!

So, even though the bug was in my code, and a pretty obvious one in retrospect, it was really helpful to be able to look at the assembly and understand WHY my code was wrong.

Cheers!

Evolution of a Logo 24 Feb 2011 6:49 AM (14 years ago)

This past month I've been working with a friend of mine, Shawn Bellah, on rebranding Galaxy Gameworks in preparation for GDC.  This is a kind of big deal, because this is the birth of the company in the public eyes, and I want to make sure it's as fun and professional as possible.

One of the important pieces of this process is the logo.  The logo should be distinctive, simple, and say something awesome about your company.

We went through a very iterative process during the logo development.  We started with a bunch of brainstorming sketches that Shawn had done, where we looked at different ideas to use with the logo.  We liked the double-G play in the company name, and geeked out on the space theme.  We looked at lots of pictures of galaxies and nebulae, and tried a few different ideas like interlocking G's, where the top of each G was an arm of a spiral galaxy, another where the G was the center of a galaxy seen edge on, another where the G was made of welded steel plates surrounding a galactic center, etc.

But I kept coming back to the first sketch that he had done to warm up, which was a solar system with the planets aligned to form the cross-bar of the G.  I felt a connection there, and I wanted to go explore the planets, and above all it just looked interesting.

So he played around with that idea, creating a galaxy suggestive of the letter G with some larger stellar objects to create interest:

 We settled on one of the variants with a nice angle, the planets in alignment and a glow in the middle:


That looked nice, but wasn't suggestive enough of the G, and was a little too complex for our purposes.  So Shawn removed the planets and the tail, and thickened up the lines considerably:


This was simple and showed off the two G's nicely, but I didn't really like the bulge on the outer G, so I used my crude art skills to trim it to show what I was thinking, and Shawn came back with half a dozen variants on what I was showing him.

At that point, both Lauren and I had been staring at it for too long to have any reasonable fresh opinions, so I showed the options to some friends who were artists, and they unanimously picked one of them.

So, a little more polish and we have our final logo!


It's clean, simple, and has the double G with a galaxy motif.  Perfect!

Ninja hacking on the iPhone 17 Feb 2011 12:00 AM (14 years ago)

I'm tracking down a crash in SDL on the iPhone, and the path is not yet clear to me, but I thought some people would enjoy the view along the way.

The crash itself happens only on the real phone, not on the simulator, and it's a crash initializing an SDL_uikitopenglview, which is a view deriving from SDL_uikitview, which in turn derives from UIView.

The callstack for the crash looks like this:
_class_getMeta ()
_class_isInitialized ()
_class_initialize ()
...
objc_msgSend_uncached ()
UIKit_GL_CreateContext () at SDL_uikitopengles.m:146

Of course everything past my code is ARM assembly, which makes it a little tricky to debug.  Luckily Apple has published the source to their Objective C runtime, so I can disassemble the functions using gdb and follow along:
http://www.opensource.apple.com/source/objc4/objc4-437.1

First, there's a couple useful things to know if you're poking around at this level:

The ARM calling conventions are that registers r0 through r3 are for parameters passed into functions, and they correspond to parameters from the left to the right. The return value of the function is also passed back through r0.

The Xcode debugging window has a nice interface with the code right there along with the local variables and registers. On the far right is a button to bring up the gdb console where you can do some pretty advanced things.

gdb quick reference:
b <name> - set a breakpoint at the beginning of the named function
s - go to the next line of code, stepping into function calls
n - go to the next line of code, skipping over function calls
si - go to the next assembly instruction
fin - run until the function returns
c - continue running until the next breakpoint
p <var> - print the value of a variable or register (e.g. $r0, $r1, etc.)
x <address> - lookup the symbol associated with an address
display <var> - print the value of a variable or register after each command 
list - list the code around the current execution

Most of these we don't need since the Xcode UI is pretty nice, but a really handy one is 'si', since that will let us step into the assembly and then use the UI to continue tracing the execution.

So first, I set a breakpoint at the line that crashes:
view = [[SDL_uikitopenglview alloc]

Then, I bring up the gdb console and use the 'si' command a few times until I get into assembly, just to see what things look like:

I'm curious what the first parameter to objc_msgSend() is, so I use 'x $r0' and it shows that it's "OBJC_CLASS_$_SDL_uikitopenglview", which is the Objective C class definition for my custom view.

Then I use the 'b' command to set a breakpoint in the _class_initialize() function, and bring up the code so I can follow along with the assembly.  When the breakpoint hits, I step into the first instruction in the function, a call to _class_getNonMetaClass(). I double check r0, and it's still my view class definition, but on return from the function, it's been set to 0!

The code that was executed is this:

static class_t *getNonMetaClass(class_t *cls)
{
    rwlock_assert_locked(&runtimeLock);
    if (isMetaClass(cls)) {
        cls = NXMapGet(uninitializedClasses(), cls);
    }
    return cls;
}

which means that somehow the class for my view didn't get into the map of classes that my program has loaded.

I did a little googling and found that Apple has a set of APIs for managing and interacting with the Objective C classes, and so I wrote a function to print them out and look for anything with SDL in it:

void print_classes()
{
    int i, numClasses;
    Class * classes;

    numClasses = objc_getClassList(NULL, 0);
    classes = malloc(sizeof(Class) * numClasses);
    numClasses = objc_getClassList(classes, numClasses);
    for (i = 0; i < numClasses; ++i) {
        char *name = class_getName(classes[i]);
        if (SDL_strstr(name, "SDL_")) {
            name; // Yay, found it!
        }
    }
    free(classes);
}

Sure enough, when I run it on the simulator I find the SDL view classes, and when I run it on the device they don't show up. If I use nm on the application binary in the app folder, I see the classes are there, in both the simulator and device binaries:
nm -m Happy | fgrep SDL_uikitopenglview
0008a287 (__TEXT,__text) non-external -[SDL_uikitopenglview context]
...
000cd06c (__DATA,__objc_data) external _OBJC_CLASS_$_SDL_uikitopenglview
000cd058 (__DATA,__objc_data) external _OBJC_METACLASS_$_SDL_uikitopenglview

So, at this point I know why the crash is happening, but I don't know why the classes aren't being loaded on the device, or how to fix it yet.

Update:  Eric Wing figured this out.  The problem is that the Objective C class definitions were in a static library and the linker wasn't bringing in all the code necessary to construct the classes.  The solution is to add -ObjC to the "Other Linker Flags" setting for your application.

Thanks Eric! :)

MPEG acceleration with GLSL 12 Feb 2011 9:59 AM (14 years ago)

Video decoding is something that people are always trying to find ways to accelerate.  Whether it's making HD video more HD or dynamically streaming video to textures in your game, we want it as fast and high quality as possible.

MPEG based codecs have basically two steps which are time consuming, the first is decoding each frame into a YUV colorspace image, and the second is converting the image from YUV to RGB.  There is lots of information available on the MPEG stream decoding and YUV colorspaces, but here I'm going to focus on the YUV to RGB conversion.

To understand how to accelerate this process, we need to understand a little about the YUV format and how the conversion is done.

YV12 images consist of 3 planes, one Y image sized WxH, and a U and V image, sized W/2 x H/2.  Put simply, the Y plane contains the luminance, which can be used alone for grayscale, and the U and V planes contain the red and blue color components, one value for each 2x2 block of output pixels.

The formula for converting from YUV to RGB is:

R = 1.164(Y - 16) + 1.596(V - 128)
G = 1.164(Y - 16) - 0.813(V - 128) - 0.391(U - 128)
B = 1.164(Y - 16)                  + 2.018(U - 128)

The basic idea for the shader is to create three different textures, one for each plane, and pull the Y, U, and V components from each texture and combine them using the above formula into the output RGB values.

The key to optimizing the shader is to recognize that the GPU shader hardware is optimized for massively parallel operations and that many of the common operations used in 3D math are optimized down to a single cycle, and then reducing number of operations as much as possible.

Looking at the formula, it can be broken down into an offset for each of the YUV components, and then a multiply and add operation on each of them, which conveniently is how a dot product is defined.  So, I simply create constants for each of the operations and put it all together!

varying vec2 tcoord;
uniform sampler2D tex0; // Y 
uniform sampler2D tex1; // U 
uniform sampler2D tex2; // V 

// YUV offset 
const vec3 offset = vec3(-0.0625, -0.5, -0.5);

// RGB coefficients 
const vec3 Rcoeff = vec3(1.164,  0.000,  1.596);
const vec3 Gcoeff = vec3(1.164, -0.391, -0.813);
const vec3 Bcoeff = vec3(1.164,  2.018,  0.000);

void main()
{
    vec3 yuv, rgb;

    // Get the Y value
    yuv.x = texture2D(tex0, tcoord).r;

    // Get the U and V values
    tcoord *= 0.5;
    yuv.y = texture2D(tex1, tcoord).r;
    yuv.z = texture2D(tex2, tcoord).r;

    // Do the color transform
    yuv += offset;
    rgb.r = dot(yuv, Rcoeff);
    rgb.g = dot(yuv, Gcoeff);
    rgb.b = dot(yuv, Bcoeff);

    // That was easy. :)
    gl_FragColor = vec4(rgb, 1.0);
}

Now the test!

I used a 1024x1050 image, converted it to YV12 and then repeatedly updated a streaming texture and displayed it on the screen.  I ran this test on a Mac Pro running Mac OS X using both MMX optimized software color conversion and OpenGL GLSL color conversion.

The code is available here:
http://www.libsdl.org/blog/files/yuvspeedtest.c

SDL_RENDER_DRIVER=software ./yuvspeedtest ~/bluemarble2k_big.bmp
Using software rendering
26.83 frames per second

SDL_RENDER_DRIVER=opengl ./yuvspeedtest ~/bluemarble2k_big.bmp
Using opengl rendering
1040.53 frames per second

Using hardware shader acceleration got almost a 50x speedup!

Fifty times?! That's right...FIFTY! OMG!!!


Resources:

• YUV colorspace description: http://en.wikipedia.org/wiki/YCbCr
• YUV format descriptions: http://www.fourcc.org/yuv.php
• YUV colorspace conversion: http://www.fourcc.org/fccyvrgb.php
• MPEG video compression: http://www.bbc.co.uk/rd/pubs/papers/paper_14/paper_14.shtml

Streaming textures with SDL 1.3 11 Feb 2011 11:47 AM (14 years ago)

I was recently asked how to use streaming textures with SDL 1.3, and while it's very simple, I didn't actually find any documentation on how to do it, so here it is!

First, why would you use a streaming texture?

Static textures are designed for sprites and backgrounds and other images that don't change much.  You update them with pixels using SDL_UpdateTexture().

Streaming textures are designed for things that update frequently, every few seconds, or every frame.  You can also update them with SDL_UpdateTexture(), but for optimal performance you lock them, write the pixels, and then unlock them.

Conceptually they're very simple to use:

1. Call SDL_CreateTexture() with the SDL_TEXTUREACCESS_STREAMING access type
2. Call SDL_LockTexture() to get raw access to the pixels
3. Do any pixel manipulation you want
4. Call SDL_UnlockTexture()
5. Use the texture in rendering normally.

You can specify any RGB/RGBA or YUV format you want and SDL or the hardware drivers will do the conversion for you on the back end if it's not supported. To get the best speed you'll probably want to create the texture in the first format listed in the renderer info, although at the time of this writing SDL_PIXELFORMAT_ARGB8888 is the optimal format for all renderers. 

You might also want to create a surface from the texture pixels if you're doing old style blitting using other SDL surfaces.  You can do this by creating a surface with no pixel data and then filling the pixel and pitch info in later:

texture = SDL_CreateTexture(renderer,
                            SDL_PIXELFORMAT_ARGB8888,
                            SDL_TEXTUREACCESS_STREAMING,
                            width, height);

surface = SDL_CreateRGBSurfaceFrom(NULL,
                                   width, height,
                                   32, 0,
                                   0x00FF0000,
                                   0x0000FF00,
                                   0x000000FF,
                                   0xFF000000);

...
SDL_LockTexture(texture, NULL,
                &surface->pixels,
                &surface->pitch);
... draw to surface
SDL_UnlockTexture(texture)


I put together a very simple example based on the running moose by Mike Gorchak:
http://hg.libsdl.org/SDL/file/default/test/teststreaming.c


Enjoy!

Fun with shaders! 8 Feb 2011 9:37 PM (14 years ago)

I just added GLSL shaders to the SDL OpenGL rendering implementation.

On my hardware this ends up being about a 200-400 FPS increase in testsprite2:

SDL_RENDER_OPENGL_SHADERS=0 ./testsprite2
4259.55 frames per second

SDL_RENDER_OPENGL_SHADERS=1 ./testsprite2
4552.88 frames per second

I also got a modest increase with testsprite, using the old SDL 1.2 API:

SDL_RENDER_OPENGL_SHADERS=0 ./testsprite
1329.16 frames per second

SDL_RENDER_OPENGL_SHADERS=1 ./testsprite
1354.20 frames per second

Woot! :)

I also noticed there's not a single example of using shaders with SDL that has full source code, so I added one:
http://hg.libsdl.org/SDL/file/default/test/testshader.c

Enjoy! :)

Texture Streaming Performance 5 Feb 2011 10:50 AM (14 years ago)

In my recent SDL 1.3 update I made it possible for the old SDL 1.2 API to be accelerated using texture streaming.

On my system on Mac OS X and Linux, this doubled performance!

Mac OS X

• SDL 1.2 testsprite: 514.22 FPS
• SDL 1.3 testsprite texture streaming with OpenGL: 1259.62 FPS
• SDL 1.3 testsprite2 (hardware accelerated):  3865.16 FPS

Linux

• SDL 1.2 testsprite:  495.48 FPS
• SDL 1.3 testsprite texture streaming with OpenGL:  1244.55 FPS
• SDL 1.3 testsprite2 (hardware accelerated):  2556.85 FPS

On my system the Windows performance got worse!

Windows

• SDL 1.2 testsprite using GDI: 1030.71 FPS
• SDL 1.3 testsprite using GDI: 1077.81 FPS
• SDL 1.3 testsprite texture streaming with OpenGL: 623.08 FPS
• SDL 1.3 testsprite texture streaming with Direct3D: 233.97 FPS
• SDL 1.3 testsprite2 (hardware accelerated with OpenGL): 3027.26 FPS
• SDL 1.3 testsprite2 (hardware accelerated with Direct3D): 4259.48 FPS

Clearly the Windows GDI drivers are heavily optimized for 2D performance, but why is the Direct3D streaming performance so poor?

Here's what I'm doing for OpenGL:
  Texture format:  GL_RGBA8, GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV
  Texture update:

I'm not doing anything fancy with pixel buffer objects, I'm just making sure that my data is in the optimal format for processing by the OpenGL drivers.

Here's what I'm doing for Direct3D:
    Device Setup:
    pparams.BackBufferCount = 1;
    pparams.SwapEffect = D3DSWAPEFFECT_DISCARD;
    pparams.PresentationInterval = D3DPRESENT_INTERVAL_IMMEDIATE;

    Texture create:
    device->CreateTexture(width, height, 1, D3DUSAGE_DYNAMIC, D3DFMT_A8R8G8B8, D3DPOOL_DEFAULT, &texture, NULL);

    Texture update:
    texture->LockRect(0, &locked, NULL, D3DLOCK_DISCARD);
    texture->UnlockRect(0);
    device->DrawPrimitiveUP(D3DPT_TRIANGLEFAN, 2,
 vertices, sizeof(*vertices));
    ...

For those who are curious, the full code can be found here:
http://www.libsdl.org/tmp/SDL-1.3.zip

So... does anyone know how to improve Direct3D texture streaming performance?

New SDL API changes 3 Feb 2011 3:51 PM (14 years ago)

I've been quiet the last week working on a massive restructuring of the SDL rendering API.  The result is a simpler, easier to use, and easier to port system.
http://forums.libsdl.org/viewtopic.php?t=6869&start=18

Whew!  Time to sleep! :)

Pointers and qualifiers 27 Jan 2011 12:38 PM (14 years ago)

I had forgotten what the rules for pointer qualifiers were, so for the ignorant and forgetful, here they are:

The stuff to the left of the * is what the pointer points at.
The stuff to the right of the * is the qualifiers on the pointer itself.

Benchmark, benchmark, benchmark 27 Jan 2011 6:52 AM (14 years ago)

I've been meaning to add a yield() function to the SDL API for a while.  I've also been mulling around with different ideas to improve the spinlocks.

Here's the current spinlock (pseudo-code):
while (locked) delay(0)

My theory was that if the lock was contended, it's better to retry a few times before sleeping.  I also figured using the OS's thread yield function was a better way of giving up the current timeslice than sleeping for 0 time.

Here was my new spinlock:
if (!locked) return
while (true)
    for (i = 0; i < 4; ++i)
       if (!locked) return
    yield()

Astonishingly, my FIFO benchmark went from 3 seconds to 10 seconds!

Thinking about this a little, it makes sense... the CPU probably doesn't see the value change in as few cycles as the loop is, so all we're really doing is wasting time in the loop.  When there's high contention, as in my FIFO test, this just means the whole system is working harder.

So, I went back to my basic spinlock, but I used a yield instead of delay(0):
while (locked) yield()

Oddly enough, my FIFO benchmark wasn't any faster, in fact it was 4 seconds instead of the original 3 seconds.  Apparently on Mac OS X sched_yield() is a more expensive function than nanosleep().

My conclusion?
Always benchmark your changes, even if they're obviously an improvement, and don't be afraid to leave well enough alone. :)

Digitally Signing Documents 26 Jan 2011 10:39 AM (14 years ago)

In the course of my business day, I frequently have to sign licensing or tax documents and e-mail them to people.

I've been looking for a paperless way to do this, and I've found a fairly easy way to do it using the GIMP (http://www.gimp.org) and OpenOffice (http://www.openoffice.org).

Setup:

1. Scan your actual signature and edit it in GIMP, converting the background to transparency using Colors -> Color to Alpha, and then save it as a PNG file.  You may need to rescale your signature to have it fit on documents, depending on the resolution of the original scan.
2. Download and install the OpenOffice PDF import extension: http://extensions.services.openoffice.org/project/pdfimport

Signing:

1. Open your PDF document in OpenOffice, which should open in the Draw program.
2. Select the Insert -> Picture -> From File... menu option and select your signature image.
3. Move it into place on the document.
4. Print the document and in the Print menu, select "Save as PDF"
5. Send it via e-mail!

There's also a really good digital signing service at DocuSign (http://www.docusign.com), and we'll probably start using that once there's enough volume to make it worthwhile.

Is Lock-Free worth it? 25 Jan 2011 11:57 PM (14 years ago)

I've spent a bunch of time the past few weeks learning about lock-free and wait-free algorithms for super fast multi-threaded data structure access.

I've had two motivations for this.  First, I wanted to vet the new SDL atomic API, and second I wanted to potentially increase the performance of the SDL event system.

In the course of learning about lockless programming, I've gained a healthy respect for people who are doing it correctly.  It's incredibly tricky to get right, and even reviewed and published papers can have subtle bugs in them.  There are a lot of subtle issues and ways multi-threaded lockless code can fail, especially on the XBox 360 where data ordering between CPUs is not guaranteed at all without expensive sync instructions.

All of this has made me wonder if it's a good idea to make a cross-platform atomic API available in the first place.

But that said, let's first see what the benefits might be...

I wrote a lock-free FIFO that modeled the behavior of the SDL event queue, and created a test that could run both lock-free and using a mutex, to simulate the way the current SDL event queue is handled.  I then added a watcher thread and single spinlock to the lock-free version to simulate a thread periodically coming in and having to do heavy duty manipulation of the queue.

The test took 4 writer threads and had each of them put 1 MILLION events on the queue, and then created 4 reader threads to pull them off and process them.  The queue was limited to a maximum of 256 events.  I defined wait states for writers if they tried to add an event and the queue was full, and defined wait states for readers if they tried to get an event and the queue was empty.

I ran the test on a 4-core Mac Pro (with 8 hardware threads), on a mostly idle system.

The results were astonishing!

FIFO test---------------------------------------

Mode: Mutex
Finished in 37.097000 sec

Writer 0 wrote 1000000 events, had 0 waits
Writer 1 wrote 1000000 events, had 0 waits
Writer 2 wrote 1000000 events, had 0 waits
Writer 3 wrote 1000000 events, had 0 waits

Reader 0 read 999998 events, had 50 waits
Reader 1 read 1000003 events, had 23 waits
Reader 2 read 999998 events, had 13 waits
Reader 3 read 1000001 events, had 7 waits

FIFO test---------------------------------------

Mode: LockFree
Finished in 0.688000 sec

Writer 0 wrote 1000000 events, had 5308 waits
Writer 1 wrote 1000000 events, had 5263 waits
Writer 2 wrote 1000000 events, had 5348 waits
Writer 3 wrote 1000000 events, had 5314 waits

Reader 0 read 1023604 events, had 7838 waits
Reader 1 read 991976 events, had 7688 waits
Reader 2 read 981770 events, had 7700 waits
Reader 3 read 1002650 events, had 7893 waits

As you can see, the lock-free version was over 50 times faster than the mutex version!

On the other hand, the mutex protected queue was able to process an event in 9 microseconds, which is well within the design specs for the SDL event queue. :)

In conclusion, lock-free algorithms are a huge benefit for code that needs to be extremely high performance and scale well across many processors.  Applications of this might be fast transaction network servers, databases, or massively parallel data processing.

Resources:
http://msdn.microsoft.com/en-us/library/ee418650%28v=vs.85%29.aspx
http://www.1024cores.net/home/lock-free-algorithms
http://www.drdobbs.com/high-performance-computing/212201163

Oh, and if you're not afraid yet, think about might what happen if you're managing dynamically allocated objects with an atomic reference count...
http://www.1024cores.net/home/lock-free-algorithms/object-life-time-management/differential-reference-counting
http://www.drdobbs.com/architecture-and-design/184401888

Weekends are important! 22 Jan 2011 12:19 PM (14 years ago)

This past week was the first week in a three week sprint I'm on to get SDL in a releasable state.  Realistically I know there will be some bigger tasks that will still need to be done, but I feel like I'll have most of the important smaller tasks and bugs and polish taken care of.  However there's a huge amount of work to be done, and to hit this goal I've been working almost non-stop for the past week.

Ahhh, weekend!

The weekend is hugely important, and I'm planning to take my weekends as family and planning time.  They give me a chance to slow down, relax, smile, and get perspective.  If I'm going so fast that I don't have time to relax on the weekend, I'm doing something fundamentally wrong and need to rethink things.

Ahhhhh. :)

/goes to hug his wife...

Multiple Gmail accounts 21 Jan 2011 3:07 PM (14 years ago)

I finished setting up Galaxy Gameworks with Google mail and apps services today, and was immediately frustrated by the inability to have my business e-mail and my personal e-mail open at the same time.

I did a little digging and found that Google has indeed made it possible to have Gmail and the core web apps open on two different accounts.  However, setting it up is a little tricky.

You can turn on this feature by going to Settings -> Accounts -> Google Account settings, and then editing the “Multiple sign-in” setting.  Once you have done this and refreshed your browser, you can click the downward arrow next to your account name in the upper right and log in with another gmail account.

Voila! :)

Keeping the "Simple" in Simple DirectMedia Layer 20 Jan 2011 11:59 PM (14 years ago)

SDL serves three types of video API users:

1. People who just want a framebuffer and use SDL 1.2 blit and direct pixel access to do the job.
2. People who just want an OpenGL context, and use OpenGL or OpenGL ES to do the job.
3. People who want a hardware accelerated 2D API

For 1 and 2, the functionality was available in SDL 1.2 and the feature set is well understood.

For 3, this is a new area that SDL 1.3 is supporting, and it's really easy to lose the "Simple" in "Simple DirectMedia Layer"

So I think here is a good time to remember that the goal of the SDL rendering API is simply:

Hardware accelerate operations that were typically done with the SDL 1.2 API.

This is tricky, since people did lots of interesting things with direct framebuffer access, but let me break it down into a feature set:

• copying images
• filling rectangles
• drawing single pixel lines
• drawing single pixel points

SDL 1.2 provided colorkey, alpha channels, and per-surface alpha, as well as nearest pixel scaling.

Again, to break that down into a feature set:

• blending for all operations
• single vertex alpha for all operations
• single vertex color for all operations
• scaling for image copy operations

It's tempting to add functionality here, but that road lies madness...