mutex ----只有等到主进程解锁后，子线程才能运行

/*mutex.c
 * function:mutex test in main,pthread
 */
#include<stdio.h>
#include<unistd.h>
#include<pthread.h>
#include<error.h>


void * pthread_fuction(void *arg);
char flag=1;
pthread_mutex_t mutex;//definite a mutex
int main(int argc,char **argv)
{

    pthread_t pth_id;
int count1=0;
printf( "This in the main :ID is  %lu\n" , pthread_self() );
//initial mutex
if(pthread_mutex_init(&mutex,NULL)!=0)
{ 
perror("Mutex initial error");
exit(1);
}
//creat pthread
        if(pthread_create(&pth_id,0,pthread_fuction,NULL)!=0)
{
perror("Thread Create error");
exit(1);
}
//lock mutex
if(pthread_mutex_lock(&mutex)!=0)
{
perror("Mutex lock error");
exit(1);
}
else
printf("Main process Lock!\n");
while(count1++<3)
{
if(flag==1)
{
printf("In Main thread is running\n");
flag=2;
}
else
{
printf("Main thread is sleeping \n");
sleep(1);
}
}
printf("main thread sleep 5 s ,then start unlock\n ");
// printf("main thread then start unlock\n ");
sleep(5);
/* if(pthread_mutex_unlock(&mutex)!=0)
{
perror("Mutex unlock Failed");
exit(1);
}
else
*/ //printf("Main thread unlock\n");
if(pthread_mutex_unlock(&mutex)==0)
printf("Main thread unlock success\n");
else
{
perror("main thread unlock fail");
exit(1);
}
//restore mutex
pthread_mutex_destroy(&mutex);


pthread_join(pth_id,NULL);//wait child thread exit
return 0;
}
void * pthread_fuction(void *arg)
{
char count2=0;
printf( "This in the child thread  :ID is  %lu\n" , pthread_self() );
//add 
sleep(1);//let main process run 
if(pthread_mutex_lock(&mutex)!=0)
// if(pthread_mutex_trylock(&mutex)!=0)
         {
                 perror("Mutex lock error");
                 exit(1);
         }
         else
        printf("Child thread  process Lock!\n");
         while(count2++<3)
        {
                 if(flag==2)
                 {
                         printf("In Child thread is running\n");
                         flag=1;
                 }
                 else
                 {
                         printf("child  thread is sleeping \n");
                       sleep(1);
                 }
         }
 
         if(pthread_mutex_unlock(&mutex)!=0)
         {
                 perror("Mutex unlock Failed");
                 exit(1);
         }
else
printf("child thread unlock\n");
pthread_exit(NULL);

}

运行结果：

 ./mutex
This in the main :ID is  3086722752
This in the child thread  :ID is  3086719888
Main process Lock!
In Main thread is running
Main thread is sleeping 
Main thread is sleeping 
main thread sleep 5 s ,then start unlock
 Child thread  process Lock!
In Child thread is running
child  thread is sleeping 
Main thread unlock success
child  thread is sleeping 
child thread unlock

可见，只有等到主进程解锁后，子线程才能运行