PThread Create不会创建线程

时间:2017-03-18 09:14:47

标签: c multithreading pthreads posix semaphore

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include "pthread.h"
#include "semaphore.h"

FILE * f;
sem_t * s1;
sem_t * s2;
int check;
int  v1;
int  v2;
int i;

static void * client (void *arg){


    sem_getvalue(s1, &v1); printf("Client pre wait(S1) in S1 => S1 = %d\n",v1);
    sem_wait(s1);
    printf("client works...\n");
    check = sem_getvalue(s1, &v1); printf("Client.wait(S1) in S1 => S1 = %d\n",v1);
    if(check != 0) printf("sem_getvalue error");


     return 0;
    }


int main(void){

    pthread_t tidc;
    pthread_t tids;
    int rc;
    int rs;

    //Semaforo 1
    s1 = (sem_t *) malloc(sizeof(sem_t));
    check = sem_init (s1, 0, 2);
    if (check != 0) perror("s1_init failed");




    sem_getvalue(s1, &v1);

    printf("Create the semaphores: S1 = %i\n",v1 );

    sem_wait(s1);
    printf("main waits\n");
    sem_getvalue(s1, &v1); printf("Main.wait(S1) in S1 => S1 = %d\n",v1);

    rc = pthread_create (&tidc, NULL, client, 0);
    printf(" thread created ==> rc= %i\n",rc);


    return 0;

   }

它返回此输出:

Create the semaphores: S1 = 2
main waits
Main.wait(S1) in S1 => S1 = 1
 thread created ==> rc= 0

有时这个:

 Create the semaphores: S1 = 2
main waits
Main.wait(S1) in S1 => S1 = 1
 thread created ==> rc= 0
Client pre wait(S1) in S1 => S1 = 1
Client pre wait(S1) in S1 => S1 = 1
client works...
Client.wait(S1) in S1 => S1 = Client.wait(S1) in S1 => S1 = 0

似乎有时会创建两个线程,有时甚至没有一个线程。我使用gcc prog.c -lpthred进行编译,甚至使用gcc -pthread prog.c

进行编译

1 个答案:

答案 0 :(得分:0)

如果一个多线程程序从一个执行到另一个执行没有做同样的事情,那可能是因为未初始化的变量(比如在非线程程序中),但也可能是因为race condition

在这种情况下,竞争条件是在线程执行和程序退出之间。

由于您在创建线程后立即退出主线程,因此线程终止(main thread exit, does other exit too?)。有时,线程有时间做某事,具体取决于操作系统状态&amp;负荷。

如果您添加一些实际处理,长时间延迟或调用pthread_join(tdic,NULL);以等待主程序中的线程终止,您将具有确定性行为。