全局变量在多线程中的使用

#include <pthread.h>
#include <stdio.h>

#define FAILURE 0
#define SUCCESS 1
#define UNS32 unsigned int
#define m_ERROR(format, args...) printf(format, ## args);//fflush(stdout);

static pthread_t   g_pthread_wait;
static pthread_t   g_pthread_signal;
static pthread_t   g_pthread_mt;
pthread_mutex_t         g_pthread_mutex;
pthread_cond_t          g_pthread_cond;

static int STATE = 0;

UNS32 pthread_initialize_cond(void){
   if ( (pthread_cond_init(&g_pthread_cond, NULL)) != 0 ) {
            m_ERROR("/t!!! ERROR : pthread_cond_init !!!/n");
          return FAILURE;
}
    return SUCCESS;
}

UNS32 pthread_initialize_mutex(void){
     if ( (pthread_mutex_init(&g_pthread_mutex, NULL)) != 0 ) {
           m_ERROR("/t!!! ERROR : pthread_mutex_init !!!/n");
         return FAILURE;
     }
     return SUCCESS;
}

void pthread_wait(void *args){
     pthread_detach(pthread_self());
    pthread_mutex_lock(&g_pthread_mutex);

    pthread_cond_wait(&g_pthread_cond, &g_pthread_mutex);
    STATE = 1;

    pthread_mutex_unlock(&g_pthread_mutex);

pthread_exit(NULL);
}

void pthread_signal(void *args){
pthread_detach(pthread_self());

      pthread_mutex_lock(&g_pthread_mutex);
      pthread_cond_signal(&g_pthread_cond);
      pthread_mutex_unlock(&g_pthread_mutex);

     while(STATE == 0)
              ;
      printf("STATE EXIT!!!/n");

       pthread_exit(NULL);
}

int main() {
pthread_initialize_cond();
pthread_initialize_mutex();

//线程1
       if (pthread_create(&g_pthread_wait , NULL, (void * (*)(void *)) pthread_wait, NULL) !=0) {
              return FAILURE;
       }

//线程2
      if (pthread_create(&g_pthread_signal , NULL, (void * (*)(void *)) pthread_signal, NULL) !=0) {
             return FAILURE;
     }

     printf("while!/n");
     while(1);
}

输出结果为：

while!
STATE EXIT!!!

分析：线程1在收到g_pthread_cond条件后，将STATE值赋为1，线程2在跳出while(STATE == 0)循环，打印STATE EXIT!!!

补充：

如果将原来的pthread_wait和pthread_signal换成如下的函数：

void pthread_wait(void *args){
        pthread_detach(pthread_self());
        pthread_mutex_lock(&g_pthread_mutex);
        pthread_exit(NULL);
}

void pthread_signal(void *args){
pthread_detach(pthread_self());

        pthread_mutex_unlock(&g_pthread_mutex);
        pthread_mutex_lock(&g_pthread_mutex);
        printf("sunhao success!!!/n");
        pthread_exit(NULL);
}

打印结果为：

while!
sunhao success!!!
说明锁可以在一个线程中加锁，而在另一个线程中进行解锁。

（如果将绿色的注释去掉的话，那么就打印不出sunhao success!!!）

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全局变量在多线程中的使用

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