使用QNX信号量实现进程间同步和互斥

本示例代码展示了在QNX系统中如何使用信号量实现进程间的同步和互斥。通过控制信号量的值来实现进程的阻塞和唤醒。使用P/V操作实现对信号量的加减操作，控制多个进程的访问。

#include <semaphore.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>

void print_msg(const char *msg)
{
    printf("%s\n", msg);
}

int main(int argc, char *argv[])
{
    sem_t* mutex; //信号量变量

    if ((mutex = sem_open("/mutex", O_CREAT, 0644, 1)) == SEM_FAILED) {
        perror("sem_open");
        exit(EXIT_FAILURE);
    }
    pid_t pid;
    pid = fork();

    if (pid < 0) { /* error occurred */
        fprintf(stderr, "Fork Failed\n");
        return 1;
    } else if (pid == 0) { /* child process */
        sem_wait(mutex);
        print_msg("child process executing critical section...");
        sleep(3);
        sem_post(mutex);
        exit(0);
    } else { /* parent process */
        sem_wait(mutex);
        print_msg("parent process executing critical section...");
        sleep(3);
        sem_post(mutex);
        print_msg("parent process exiting critical section...");
        sem_close(mutex);
        sem_unlink("/mutex");
        exit(0);
    }

    return 0;
}

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