Linux 使用 pthread 进行进程间互斥
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Interprocess mutex with pthreads
提问by MetallicPriest
I want to use a mutex which will be used to synchronize access to some variables residing in the memory shared b/w two different processes. How can I achieve that. Code sample to perform that will be very appreciated.
我想使用一个互斥锁，它将用于同步对驻留在共享 b/w 两个不同进程的内存中的一些变量的访问。我怎样才能做到这一点。要执行的代码示例将不胜感激。
采纳答案by cnicutar
Use a POSIX semaphoreinitialized to (See below) Use 1instead.sem_initfor unnamed semaphores or sem_openfor named ones.
使用初始化为的POSIX 信号量（见下文）1。sem_init用于未命名的信号量或sem_open命名的信号量。
sem_t sem;
/* initialize using sem_init or sem_open */
sem_wait(&sem);
/* critical region */
sem_post(&sem);
Many years after initially posting this answer, it has to be updated.
在最初发布此答案多年后，必须对其进行更新。
Mutexes should actually be used instead of semaphores. R and kuga's comments (copied verbatim below) explain why. In particular I find kuga's mention that mutexes can only be posted by their locking thread most compelling.
实际上应该使用互斥体而不是信号量。R 和 kuga 的评论（在下面逐字复制）解释了原因。特别是我发现 kuga 提到的互斥锁只能post通过它们的锁定线程进行编辑，这点最引人注目。
R
电阻
sem_init requires a nonzero pshared argument to be shared, just like a mutex would require the pshared attribute. There's no reason to prefer semaphores over mutexes for this, and in fact mutexes would be better because you could use a robust mutex which allows you to handle the (very real!) case where one process dies while holding the lock.
sem_init 需要共享一个非零的 pshared 参数，就像互斥锁需要 pshared 属性一样。没有理由为此更喜欢信号量而不是互斥锁，实际上互斥锁会更好，因为您可以使用强大的互斥锁，它允许您处理（非常真实！）一个进程在持有锁时死亡的情况。
kuga
库加
Additionally to R..`s post, a mutex can only be posted by the thread that locks it. This is often required and a semaphore does not provide this feature. So this is not the correct answer, Jeff′s answer should be flagged as the correct answer.
除了 R.. 的帖子外，互斥锁只能由锁定它的线程发布。这通常是必需的，而信号量不提供此功能。所以这不是正确答案，杰夫的答案应该被标记为正确答案。
回答by Jeff
The following example demonstrates the creation, use and destruction of a Pthread interprocess mutex. Generalizing the example for multiple processes is left as an exercise for the reader.
以下示例演示了 Pthread 进程间互斥锁的创建、使用和销毁。将多个进程的示例概括为读者的练习。
#include <pthread.h>
pthread_mutex_t shm_mutex;
int main(void)
{
int err;
pthread_mutexattr_t attr;
err = pthread_mutexattr_init(&attr); if (err) return err;
err = pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_SHARED); if (err) return err;
err = pthread_mutex_init(&shm_mutex, &attr); if (err) return err;
err = pthread_mutexattr_destroy(&attr); if (err) return err;
err = pthread_mutex_lock(&shm_mutex); if (err) return err;
err = pthread_mutex_unlock(&shm_mutex); if (err) return err;
err = pthread_mutex_destroy(&shm_mutex); if (err) return err;
return 0;
}
