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Apr 28, 2009 
I know, I know. It has been over a month since my last post. Sadly, this graduate project of mine has been taking up all of my time.
Of course the time spent has not been a waste. In fact, it has been far from it. Part of the project involves users participating in a multiplayer trivia game done in Adobe Flash. The idea is that Flash will communicate with PHP via ZendAMF and PHP will talk to a C++ server via network packets. Since I haven’t written in C++ in ~3-4 years, it has taken me a bit to get back into the hang of things.
Things have changed since the last time I wrote in C++, especially because now I’m writing for a Linux OS, using direct network communication, and running in a threaded environment. I followed some people’s advice and started to look into the Boost Libraries. After about a week of frustration working with Boost.Thread and Boost.ASIO, I realized that everything I need to do can be done with pthread.h and sys/socket.h.
In the end it was primarily my fault as I didn’t realize that Boost was designed to make things work on different platforms without rewriting OS specific code. The problem is, the simple things I needed to do are therefore much more confusing to write and the developers didn’t produce the best example of documentation.
So after ditching Boost completly, I did a little bit of research to find the appropriate method for locking in muti-threaded environments for Linux. With pthread, the locking is extremely easy. Here are some basic examples:
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// This is the include file you need for this to work
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#include <pthread.h>
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// If you need a mutex for an entire class (static), you can
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// easily declare it with the PTHREAD_MUTEX_INITIALIZER macro.
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static pthread_mutex_t mutex_test = PTHREAD_MUTEX_INITIALIZER;
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// Otherwise, just declare it with the type pthread_mutex_t
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pthread_mutex_t mutex_test;
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// In this case, you will have to initialize it with this call
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// The second parameter is for attributes, in this case
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// we want only the default attributes, i.e. NULL
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pthread_mutex_init( &mutex_test, NULL );
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// This function will cause the mutex to lock (if available)
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// or wait in a deadlock until it becomes available.
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pthread_mutex_lock( &mutex_test );
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// Then this will unlock the mutex for other threads to use.
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pthread_mutex_unlock( &mutex_test );
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// Finally, we can destroy a mutex with this last call.
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pthread_mutex_destroy( &mutex_test );
Again, these are basic examples. If you wanted to look deeper into locking, you can even specify mutex types (Error Checking, Recursive, etc.)
Oh, and by the way: remember to compile with -pthread
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