关于多线程：命名 POSIX 信号量的问题

Issues with named POSIX semaphore

我正在尝试使用 POSIX 命名信号量来确保我的可执行文件只有一个实例可以运行。但是我遇到了麻烦；信号量的值始终为 0，因此它总是阻塞。

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#include <semaphore.h> /* required for semaphores */
#include <stdio.h>
#include <unistd.h> /* usleep */
#include <fcntl.h> // O_EXCL
#include
#include <stdlib.h> /* exit, EXIT_FAILURE */

int main(int argc, char *argv[])
{
int ret;
int i;
sem_t* semaphore;

semaphore = sem_open("/mysemaphore", O_EXCL, 0777 /*0644*/, 2);
printf("sem_open returned %p at line %u\
", semaphore, __LINE__);

// if it exists, open with"open", and parameters will be ignored (therefore given as 0)
if(!semaphore)
{
semaphore = sem_open("/mysemaphore", O_CREAT, 0, 0);
printf("sem_open returned %p at line %u\
", semaphore, __LINE__);
}

// either of the above calls should have given us a valid semaphore
assert(semaphore);

// read its value time and again
ret = sem_getvalue(semaphore, &i);
printf("sem_getvalue returned %i at line %u, value is %i\
", ret, __LINE__, i);

// ....

输出：

1 2	sem_open returned 0x8003a4e0 at line 36 sem_getvalue returned 0 at line 50, value is 0

平台：Cygwin 1.7.33-2

使用以下命令构建：

1	gcc Main.c -o Main -lpthread

非常感谢您的帮助！