Книга: Programming with POSIX® Threads

2.2.2 Startup

2.2.2 Startup

Once a thread has been created, it will eventually begin executing machine instructions. The initial sequence of instructions will lead to the execution of the thread start function that you specified to pthread_create. The thread start function is called with the argument value you specified when you created the thread. In lifecycle.c, for example, the thread begins executing user code at function thread_routine, with the formal parameter argument having a value of NULL.

In the initial thread, the thread "start function" (main) is called from outside your program; for example, many UNIX systems link your program with a file called crt0.o, which initializes the process and then calls your main. This is a minor implementation distinction, but it is important to remember because there are a few ways in which the initial thread is different. For one thing, main is called with different arguments than a thread start function: the program's argument array (argc and argv) instead of a single void* argument. For another thing, when a thread start function returns, the thread terminates but other threads continue to run. When the function main returns in the initial thread, the process will be terminated immediately. If you want to terminate the initial thread while allowing other threads in the process to continue running, call pthread_exit instead of returning from main.

Another important difference to remember is that on most systems, the initial thread runs on the default process stack, which can grow to a substantial size. "Thread" stacks may be much more limited on some implementations, and the program will fail with a segmentation fault or bus error if a thread overflows its stack.

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