cnd_signal函数

/*函数cnd_signal范例*/

/*
** 该例子创建了4个新线程，
** 其中3个线程用于修改number的值，第4个线程处于等待状态；
** 如果number的值大于等于LIMIT，第4个线程输出number的值。
*/

#ifdef __STDC_NO_THREADS__
#error "Implementation does not support multi-threads."
#endif

#include <stdio.h>
#include <stdlib.h>
#include <threads.h>

#define LIMIT 100       //解锁因条件变量而阻塞的线程的条件。
#define THREADS 4       //线程数。

unsigned int number = 0;        //如果number≥LIMIT，解锁因条件变量而阻塞的线程。
mtx_t mutex;                    //互斥。
cnd_t conditionVariable;        //条件变量。

/*操作number的函数。*/
int funcProcess(void *arg)
{
    do
    {
        mtx_lock(&mutex);
        
        /*如果条件满足就解锁因条件变量而阻塞的线程。*/
        if(number >= LIMIT)
        {
            cnd_signal(&conditionVariable);
            mtx_unlock(&mutex);
            
            thrd_exit(0);
        }
        number += *((unsigned int *)arg);
        
        mtx_unlock(&mutex);
    }while(number < LIMIT);
}

/*等待number值满足条件的函数。*/
int funcWait(void *arg)
{
    mtx_lock(&mutex);
    while(number < LIMIT)
    {
        cnd_wait(&conditionVariable, &mutex);
    }
    puts("Receive condition signal.");
    printf("number = %u\n", number);
    mtx_unlock(&mutex);
    
    thrd_exit(0);
}

int main(void)
{
    thrd_t threadId[THREADS];       //线程标识符。
    unsigned int data[THREADS-1] = {3, 6, 9};
    
    /*初始化条件变量。*/
    if(cnd_init(&conditionVariable) != thrd_success)
    {
        perror("cnd_init");
        exit(EXIT_FAILURE);
    }
    
    /*初始化互斥。*/
    if(mtx_init(&mutex, mtx_plain) != thrd_success)
    {
        perror("mtx_init");
        exit(EXIT_FAILURE);
    }
    
    /*创建新线程。*/
    for(int i=0; i<THREADS-1; ++i)
    {
        if(thrd_create((threadId+i), funcProcess, (data+i)) != thrd_success)
        {
            perror("thrd_create");
            exit(EXIT_FAILURE);
        }
    }
    
    if(thrd_create((threadId+THREADS-1), funcWait, NULL) != thrd_success)
    {
        perror("thrd_create");
        exit(EXIT_FAILURE);
    }
    
    /*连接线程。*/
    for(int i=0; i<THREADS; ++i)
    {
        thrd_join(threadId[i], NULL);
    }
    
    /*销毁条件变量和互斥。*/
    cnd_destroy(&conditionVariable);
    mtx_destroy(&mutex);
    
    return 0;
}