Linux多线程同步——信号量

线程同步

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同步主线程与子线程

test.c
#include <pthread.h>
#include <sys/syscall.h>
#include <fcntl.h>
#include <semaphore.h>
#include <stdlib.h>
#include <stdio.h>

void* ret_result_thread1;
sem_t *sem;

void* thread1Func(void* arg)
{
printf("childThread id:%u is running\n", syscall(SYS_gettid));
         sleep(2);
         sem_post(sem);
         pthread_exit((void*)0);

}

int main(int argc, char** argv)
{

printf("main thread start\n");

const char* semName="sem_name";
      sem = sem_open(semName,O_CREAT,0644,0);

      pthread_t thread1;
int ret1;

if( (ret1 = pthread_create(&thread1,NULL,thread1Func,NULL)) != 0)
      {
             perror("thread1 create failed");
      }

      sem_wait(sem);
printf("main thread end\n");
      pthread_join(thread1,ret_result_thread1);

      sem_close(sem);
      sem_unlink(semName);      

return 0;
}

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子线程之间的同步

使用单个信号量

#include <pthread.h>
#include <sys/syscall.h>
#include <fcntl.h>
#include <semaphore.h>
#include <stdlib.h>
#include <stdio.h>

void* ret_result_thread1;
void* ret_result_thread2;
sem_t *sem;

void* thread1Func(void* arg)
{
printf("childThread1 is running\n");
         sleep(2);
         sem_post(sem);
         pthread_exit((void*)0);         
}

void* thread2Func(void* arg)
{
         sem_wait(sem);
printf("childThread2 is running\n"); 
         sleep(2);
         pthread_exit((void*)0);                 
}

int main(int argc, char** argv)
{

printf("main thread start\n");

const char* semName="sem_name";
      sem = sem_open(semName,O_CREAT,0644,0);

      pthread_t thread1,thread2;
int ret1;
int ret2;
if( (ret1 = pthread_create(&thread1,NULL,thread1Func,NULL)) != 0)
      {
             perror("thread1 create failed");
      }

if( (ret2 = pthread_create(&thread2,NULL,thread2Func,NULL)) != 0)
      {
             perror("thread2 create failed");
      }

printf("main thread end\n");

      pthread_join(thread1,ret_result_thread1);
      pthread_join(thread2,ret_result_thread2); 

      sem_close(sem);
      sem_unlink(semName);      
return 0;
}

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使用两个信号量

test.c
#include <pthread.h>
#include <sys/syscall.h>
#include <fcntl.h>
#include <semaphore.h>
#include <stdlib.h>
#include <stdio.h>

void* ret_result_thread1;
void* ret_result_thread2;
sem_t *sem1;
sem_t *sem2;

void* thread1Func(void* arg)
{
         sem_wait(sem1);
printf("childThread1 is running\n");
         sleep(2);
         sem_post(sem2);
         pthread_exit((void*)0);

}

void* thread2Func(void* arg)
{
         sem_wait(sem2);
printf("childThread2 is running\n"); 
         sleep(2);
         sem_post(sem1);
         pthread_exit((void*)0);                  
}

int main(int argc, char** argv)
{

printf("main thread start\n");
const char* semName1="sem_name1";
      sem1 = sem_open(semName1,O_CREAT,0644,1);

const char* semName2="sem_name2";
      sem2 = sem_open(semName2,O_CREAT,0644,0);

      pthread_t thread1,thread2;
int ret1;
int ret2;
if( (ret1 = pthread_create(&thread1,NULL,thread1Func,NULL)) != 0)
      {
             perror("thread1 create failed");
      }

if( (ret2 = pthread_create(&thread2,NULL,thread2Func,NULL)) != 0)
      {
             perror("thread2 create failed");
      }

printf("main thread end\n");

      pthread_join(thread1,ret_result_thread1);
      pthread_join(thread2,ret_result_thread2); 

      sem_close(sem1);
      sem_close(sem2);

      sem_unlink(semName1);
      sem_unlink(semName2);      
return 0;
}

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主线程运行结束后，线程1开始运行，休眠2秒后开始运行线程2