c - 我的信号量形式 semaphore.h 仅在 CTRL-Z fg 之后工作

Question

我有一个程序，它在一个进程中准备一些配置，然后在父进程中读取这些配置。为了同步它们，我使用 semaphore.h 库中的信号量。但即使在我 sem_post 之后，它似乎也在 sem_wait 中永远等待。不过，在我执行 ctrl-z 和 fg 之后它就可以工作了。这是为什么？谁能告诉我我的代码有什么问题吗？我的操作系统是 Lubuntu

信号量1.h

#ifndef _DNSS_H_
#define _DNSS_H_

#include <pthread.h>
#include <semaphore.h>
#include <time.h>
#include <sys/types.h>

typedef struct configs
{
    int i;
    sem_t sem;
} CONFIGS;


void init_config(CONFIGS *_configs);
//initiates the threadpool 
int init_thread_pool(CONFIGS *configs);

#endif

Semaphore_1.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <string.h>
#include <sys/shm.h>
#include <sys/ipc.h>
#include <sys/types.h>
#include <semaphore.h>
#include <pthread.h>
#include "semaphore1.h"



void init_config(CONFIGS *_configs)
{
    sem_init(&(_configs->sem),1,0); //Creaates a semaphore that is opened  when the configs are read to shared memory

    _configs->i=2;

    fprintf(stderr, "Result of sem_post:%d\n", sem_post(&(_configs->sem)));
}

Semaphore_2.c

#include"semaphore1.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>


int init_thread_pool( CONFIGS *configs)
{
    int aux;

    fprintf(stderr, "Value of sem_wait():%d\n", sem_wait(&(configs->sem)));

    printf("Threadpool initiated with %d threads!", configs->i);

    return 1;
}

Semaphore_main.c

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<unistd.h>
#include<sys/types.h>
#include "semaphore1.h"
#include <sys/ipc.h>
#include <sys/shm.h>

int main(int argc, char *argv[])
{
    pid_t config_pid; //will hold the configuration process id
    int _shmid_configs;
    CONFIGS *_configs;

    _shmid_configs =shmget( IPC_PRIVATE, 
                             sizeof(CONFIGS), IPC_CREAT|0666); //initializes the shared memory

    if( _shmid_configs == -1)
    {
        perror("Error creating shared memory");
    }
    _configs=shmat(_shmid_configs, NULL,0); //maps the shared memory created to the processp and the config structure
    if( _configs == ( CONFIGS*)-1)
    {
        perror("Error at shmat");
    }

    //initialization of the processes
    config_pid = fork();
    if( config_pid < 0)
    {
        perror("Failed creating configuration manager process");
    }
    else if( config_pid == 0)
    {
        init_config(_configs);
        printf("Im config!\n");
        return 0;
    }

    //CODE FOR THE gestor de pedidos
    printf("right before the threadpool! Configs has a lmit of %d theads\n", _configs->i);
    init_thread_pool(_configs);
    printf("im parent and im out\n");
    sem_destroy(&_configs->sem);
    return 0;
}

编译为gcc -g -pthread Semaphore_2.c Semaphore_main.c Semaphore_1.c -o deb

输出:

./deb
right before the threadpool! Configs has a lmit of 0 theads
Result of sem_post:0
Im config!
^Z
[1]+  Stopped                 ./deb
fg
./deb
Value of sem_wait():0
Threadpool initiated with 2 threads!im parent and im out

Answer 1

sem_init() 应该在 fork() 之前调用。

在您当前的代码中，父线程中的 init_thread_pool(_configs); 可以在 init_config() 之前被调用，即您将等待未初始化的信号量。这是未定义的行为。