为什么信号量对象未初始化

Question

我正在学习使用信号量对象。但我无法初始化它。sem_init函数始终返回值 -1 风雨无阻。

返回值 -1 表示第一个参数不是有效的指针，比如我的引用。但是我在代码中找不到缺少打印。我在OS X上用Xcode编译了我的代码。

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
void * thread_snd(void *arg);
void * thread_rcv(void* arg);
sem_t bin_sem;
int number = 0;
char thread1[] = "A thread";
char thread2[] = "B thread";
char thread3[] = "C thread";
int main(int argc, char** argv)
{
    pthread_t t1, t2 ,t3;
    void *thread_result;
    int state;
    state       =   sem_init(&bin_sem, 0, 0);
    if(state != 0)
    {
        puts("fail to initialize semaphore");
        exit(1);
    }
    pthread_create(&t1, NULL, thread_snd, &thread1);
    pthread_create(&t2, NULL, thread_rcv, &thread2);
    pthread_create(&t3, NULL, thread_rcv, &thread3);
    pthread_join(t1, &thread_result);
    pthread_join(t2, &thread_result);
    pthread_join(t3, &thread_result);
    printf("final number : %d n", number);
    sem_destroy(&bin_sem);
    return 0;
}
void * thread_snd(void * arg)
{
    int i;
    for(i = 0 ; i < 4; i++)
    {
        while(number != 0)
            sleep(1);
        number++;
        printf("execution : %s, number : %d n", (char*) arg, number);
        sem_post(&bin_sem);
    }
}
void * thread_rcv(void* arg)
{
    int i;
    for(i = 0 ; i < 2; i++)
    {
        sem_wait(&bin_sem);
        number--;
        printf("execution : %s number : %d n", (char*)arg, number);
    }
}

Answer 1

在 Mac OS X （10.6.8） 上没有sem_init()和sem_destroy()。

请改用sem_open()和sem_unlink()。

/*
cat semaphore_test.c
source:
"Why semaphore object is not initialized?", 
https://stackoverflow.com/questions/13834367/why-semaphore-object-is-not-initialized
compiled on Mac OS X 10.6.8 with:
gcc -ansi -pedantic -std=gnu99 -Os -Wall -Wextra -Wshadow -Wpointer-arith -Wcast-qual  -Wstrict-prototypes 
    -Wmissing-prototypes -Wformat=2 -Wreturn-type -Wunreachable-code -finline  -l pthread -o semaphore_test semaphore_test.c
./semaphore_test
*/
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
void * thread_snd(void *arg);
void * thread_rcv(void* arg);
//sem_t bin_sem;
static sem_t *bin_sem;
static const char *semname = "Semaphore";
static int number = 0;
char thread1[] = "A thread";
char thread2[] = "B thread";
char thread3[] = "C thread";
int main(void)
{
    pthread_t t1, t2 ,t3;
    void *thread_result;
    int state;
/*
    state  =  sem_init(&bin_sem, 0, 0);
    if(state != 0)
    {
        puts("fail to initialize semaphore");
        exit(1);
    }
*/
    bin_sem = sem_open(semname, O_CREAT, 0777, 0);
    if (bin_sem == SEM_FAILED)
    {
        fprintf(stderr, "%sn", "ERROR creating semaphore semname");
        exit(EXIT_FAILURE);
    }
    pthread_create(&t1, NULL, thread_snd, &thread1);
    pthread_create(&t2, NULL, thread_rcv, &thread2);
    pthread_create(&t3, NULL, thread_rcv, &thread3);
    pthread_join(t1, &thread_result);
    pthread_join(t2, &thread_result);
    pthread_join(t3, &thread_result);
    printf("final number : %d n", number);
    //sem_destroy(&bin_sem);
    sem_unlink(semname);
    return 0;
}
void * thread_snd(void * arg)
{
    int i;
    for(i = 0 ; i < 4; i++)
    {
        while(number != 0)
            sleep(1);
        number++;
        printf("snd execution : %s, number : %d n", (char*) arg, number);
        //sem_post(&bin_sem);
        sem_post(bin_sem);
    }
}
void * thread_rcv(void* arg)
{
    int i;
    for(i = 0 ; i < 2; i++)
    {
        //sem_wait(&bin_sem);
        sem_wait(bin_sem);
        number--;
        printf("rcv execution : %s number : %d n", (char*)arg, number);
    }
}

另请参阅：

• 在 OS X 上sem_init
• 使用信号量的程序在Linux上运行良好...Mac OS X 上的意外结果