Linux线程同步---信号量初始化

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最新推荐文章于 2024-11-26 19:11:07 发布

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原文链接：http://www.cnblogs.com/farbeyond/p/4477510.html

本文深入探讨了 Linux 系统中用于初始化无名信号量的 sem_init 函数，包括其语法、参数解释、返回值以及可能出现的错误情况。详细介绍了信号量在进程间共享与内存映射下的应用，并提供了 POSIX 标准的符合性说明。

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SEM_INIT(3) Linux Programmer's Manual SEM_INIT(3)

NAME sem_init - initialize an unnamed semaphore

SYNOPSIS #include <semaphore.h>

int sem_init(sem_t *sem, int pshared, unsigned int value);

Link with -lrt or -pthread.

DESCRIPTION sem_init() initializes the unnamed semaphore at the address pointed to by sem. The value argument specifies the initial value for the sema‐ phore.

The pshared argument indicates whether this semaphore is to be shared between the threads of a process, or between processes.

If pshared has the value 0, then the semaphore is shared between the threads of a process, and should be located at some address that is visible to all threads (e.g., a global variable, or a variable allo‐ cated dynamically on the heap).

If pshared is nonzero, then the semaphore is shared between processes, and should be located in a region of shared memory (see shm_open(3), mmap(2), and shmget(2)). (Since a child created by fork(2) inherits its parent's memory mappings, it can also access the semaphore.) Any process that can access the shared memory region can operate on the semaphore using sem_post(3), sem_wait(3), etc.

Initializing a semaphore that has already been initialized results in undefined behavior.

RETURN VALUE sem_init() returns 0 on success; on error, -1 is returned, and errno is set to indicate the error.

ERRORS EINVAL value exceeds SEM_VALUE_MAX.

ENOSYS pshared is nonzero, but the system does not support process- shared semaphores (see sem_overview(7)).

CONFORMING TO POSIX.1-2001.

NOTES Bizarrely, POSIX.1-2001 does not specify the value that should be returned by a successful call to sem_init(). POSIX.1-2008 rectifies this, specifying the zero return on success.

SEE ALSO sem_destroy(3), sem_post(3), sem_wait(3), sem_overview(7)

COLOPHON This page is part of release 3.35 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://man7.org/linux/man-pages/.

Linux 2008-07-27 SEM_INIT(3)

转载于:https://www.cnblogs.com/farbeyond/p/4477510.html