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    <p>I am exactly in this situation: I wrote a library with a global lock (many threads, but only one running at a time in the library) and am refactoring it to support concurrency.</p> <p>I have read books on the subject but what I learned stands in a few points:</p> <ol> <li><strong>think parallel</strong>: imagine a crowd passing through the code. What happens when a method is called while already in action ?</li> <li><strong>think shared</strong>: imagine many people trying to read and alter shared resources at the same time.</li> <li><strong>design</strong>: avoid the problems that points 1 and 2 can raise.</li> <li>never think you can ignore edge cases, they will bite you hard.</li> </ol> <p>Since you cannot proof-test a concurrent design (because thread execution interleaving is not reproducible), you have to ensure that your design is robust by carefully analyzing the code paths and <strong>documenting</strong> how the code is supposed to be used.</p> <p>Once you understand how and where you should bottleneck your code, you can read the documentation on the tools used for this job:</p> <ol> <li>Mutex (exclusive access to a resource)</li> <li>Scoped Locks (good pattern to lock/unlock a Mutex)</li> <li>Semaphores (passing information between threads)</li> <li>ReadWrite Mutex (many readers, exclusive access on write)</li> <li>Signals (how to 'kill' a thread or send it an interrupt signal, how to catch these)</li> <li>Parallel design patterns: boss/worker, producer/consumer, etc (see <a href="http://www.cs.wustl.edu/~schmidt/patterns-ace.html" rel="noreferrer">schmidt</a>)</li> <li>platform specific tools: openMP, C blocks, etc</li> </ol> <p>Good luck ! Concurrency is fun, just take your time...</p>
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    1. POWhat are the "things to know" when diving into multi-threaded programming in C++
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    1. COConcurrency fun!!?? Man, you are brave :-)
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    2. CO@Ariel: it's fun IF you accept to slow down, think and become creative. Like every difficult task, it's fun if you give yourself the time it needs to do things right.
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    3. COI agree. I find writing MT code much more interesting than single threaded.
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