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IBM developerWorks: POSIX threads explained - A simple and nimble tool for memory sharing

Aug 06, 2000, 16:56 (0 Talkback[s])
(Other stories by Daniel Robbins)


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"POSIX (Portable Operating System Interface) threads are a great way to increase the responsiveness and performance of your code. In this series, Daniel Robbins shows you exactly how to use threads in your code. A lot of behind-the-scenes details are covered, so by the end of this series you'll really be ready to create your own multithreaded programs."

"Knowing how to properly use threads should be part of every good programmer's repertoire. Threads are similar to processes. Threads, like processes, are time-sliced by the kernel. On uniprocessor systems the kernel uses time slicing to simulate simultaneous execution of threads in much the same way it uses time slicing with processes. And, on multiprocessor systems, threads are actually able to run simultaneously, just like two or more processes can."

"So why is multithreading preferable to multiple independent processes for most cooperative tasks? Well, threads share the same memory space. Independent threads can access the same variables in memory. So all of your program's threads can read or write the declared global integers. If you've ever programmed any non-trivial code that uses fork(), you'll recognize the importance of this tool. Why? While fork() allows you to create multiple processes, it also creates the following communication problem: how to get multiple processes, each with their own independent memory space, to communicate. There is no one simple answer to this problem. While there are many different kinds of local IPC (inter-process communication), they all suffer from two important drawbacks...."

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