Embed Size (px)
Citation preview
Multi-Threading and Load Balancing
Compiled by Paul TaylorCSE3AGRStolen mainly from Orion Granatir
http://www.gamasutra.com/php-bin/article_display.php?story=4006
What changed?
• Single Thread Computer games have been used since day 0
• The person to blame is Gordon Moore*
* Not really it just feels good to blame someone!
Moore’s Law
• http://en.wikipedia.org/wiki/File:Transistor_Count_and_Moore%27s_Law_-_2008.svg
•The Complexity of IC’s will go up exponentially•We mutilated this into CPU speed will increase expo.•This all F*#ked up a few years ago when we started pushing the boundaries of transistor miniaturisation•To keep the processing increase we went with Multi core processors
It all goes bad....• http://www.gamasutra.com/php-bin/article_display.php?story=4006
Multi-Core and Threading• http://www.gamasutra.com/php-bin/article_display.php?story=4006
Network Assimilation• http://www.gamasutra.com/php-bin/article_display.php?story=4006
Processes and Threads
The first crappy threading
code you’ll see
CATCTATCATTCTATCTACTATCATCTACTATCTACTATCTACTCT
TACTCAT
Distributing Load (You need to manage your employees)
That was a better Threading ModelBut still not good enough for
today's machines
Distributing Load even more!
Learning to ShareAll cats need the Shovel for their
Quest
Learning to ShareCat has the Shovel
Learning to ShareCat has the Loot
This is what Thread Locking is for
Now how do we go about locking them??
Critical Sections
• When one thread enters the critical section, the others will have to wait......
Critical Sections
• And wait....
• And wait...
Critical Sections
• Keep them small!!!• A lot of CPU time can be
wasted waiting.... And waiting...
Mutexs and Semaphores
Mutexs and Semaphores
Mutexs and Semaphores
Mutexs and Semaphores
Mutexs and Semaphores
Mutexs and Semaphores
• A Semaphore is like usingMultiple tokens (it retains a value)• Critical Sections are fastest, but limited to one
process• Mutexs are slower, but globally accessible• Semaphores are great for things like allocating
your memory buffers
Events
Events
Events
Events
Events
Events
Atomic Operations
• http://www.breadonthewaters.com/add/0888_nuclear_explosion_large_clipart.jpg
Atomic Operations
5 + 1 + 1 + 1 = 8
Atomic Operations
5 + 1 + 1 + 1 = 6!!
Atomic Operations
• This is why we need atomic operations
Atomic Operations
• This is why we need atomic operations
Deadlocks
Deadlocks
Deadlocks
Race Conditions
• The ‘race’ is a term for when your code expects threads to return in order, and they don’t!!!
Race Conditions
Race Conditions
Race Conditions
Network Code Example
Network Code Example
Network Code Example
Network Code Example
Network Code Example
Network Code Example
• The Main thread would then need to wait for all Network threads to finish before it resets the NetworkUpdateEvent and continues
• How would you solve this?
References
• http://www.gamasutra.com/php-bin/article_display.php?story=4006
