利用POSIX互斥锁、条件变量，和内存映射文件，实现的信号量机制，用于进程间的同步。
/* sem.h */ struct semaphore { pthread_mutex_t lock; pthread_cond_t nonzero; unsigned count; }; typedef struct semaphore semaphore_t; semaphore_t* semaphore_create(char *semaphore_name); semaphore_t* semaphore_open(char *semaphore_name); void semaphore_post(semaphore_t *semap); void semaphore_wait(semaphore_t *semap); void semaphore_close(semaphore_t *semap); /* sem.c */ #include <sys/types.h> #include <sys/stat.h> #include <sys/mman.h> #include <fcntl.h> #include <pthread.h> #include "sem.h" semaphore_t* semaphore_create(char *semaphore_name) { int fd = open(semaphore_name, O_RDWR | O_CREAT | O_EXCL, 0666); if (fd < 0) return (NULL); (void) ftruncate(fd, sizeof(semaphore_t)); pthread_mutexattr_t psharedm; pthread_condattr_t psharedc; (void) pthread_mutexattr_init(&psharedm); (void) pthread_mutexattr_setpshared(&psharedm, PTHREAD_PROCESS_SHARED); (void) pthread_condattr_init(&psharedc); (void) pthread_condattr_setpshared(&psharedc, PTHREAD_PROCESS_SHARED); semaphore_t* semap = (semaphore_t *) mmap(NULL, sizeof(semaphore_t), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); close (fd); (void) pthread_mutex_init(&semap->lock, &psharedm); (void) pthread_cond_init(&semap->nonzero, &psharedc); // 我觉得应该给个大于零的初值 semap->count = 0; return (semap); } semaphore_t* semaphore_open(char *semaphore_name) { int fd = open(semaphore_name, O_RDWR, 0666); if (fd < 0) return (NULL); semaphore_t* semap = (semaphore_t *) mmap(NULL, sizeof(semaphore_t), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); close (fd); return (semap); } void semaphore_post(semaphore_t *semap) { pthread_mutex_lock(&semap->lock); // 计数为零，说明可能有线程已经阻塞在该条件变量上 if (semap->count == 0) { pthread_cond_signal(&semapx->nonzero); } semap->count++; pthread_mutex_unlock(&semap->lock); } void semaphore_wait(semaphore_t *semap) { pthread_mutex_lock(&semap->lock); // 计数为零，说明已无资源，等待 while (semap->count == 0) { pthread_cond_wait(&semap->nonzero, &semap->lock); } semap->count--; pthread_mutex_unlock(&semap->lock); } void semaphore_close(semaphore_t *semap) { munmap((void *) semap, sizeof(semaphore_t)); }