PThread Create 不创建线程

Question

#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returns这个输出：

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

有时这样：

 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，有时不会创建一个。我用 gcc prog.c -lpthred 甚至 gcc -pthread prog.c

编译

Answer 1

如果多线程程序从一次执行到另一次执行不做同样的事情，可能是因为未初始化的变量（如在非线程程序中），但也可能是因为 race condition .

在那种情况下，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，因此线程被终止 (main thread exit, does other exit too?)。有时，线程有时间做一些事情，这取决于 OS 状态和负载。

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，您将获得确定性行为。

PThread Create 不创建线程

PThread Create doesn't create a thread

c

multithreading

posix

semaphore

pthreads