3 int pthread_cond_timedwait(pthread_cond_t *cond,pthread_mutex_t *mutex,const timespec *abstime);
4 int pthread_cond_destroy(pthread_cond_t *cond);
5 int pthread_cond_signal(pthread_cond_t *cond);
6 int pthread_cond_broadcast(pthread_cond_t *cond); //解除所有线程的阻塞
(1)初始化. init()或者pthread_cond_t cond=PTHREAD_COND_INITIALIER;属性置为NULL
(2)等待条件成立. pthread_cond_wait,pthread_cond_timedwait.
wait()释放锁,并阻塞等待条件变量为真
timedwait()设置等待时间,仍未signal,返回ETIMEOUT(加锁保证只有一个线程wait)
(3)激活条件变量:pthread_cond_signal,pthread_cond_broadcast(激活所有等待线程)
(4)清除条件变量:destroy; 无线程等待,否则返回EBUSY
int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);
int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex, const struct timespec *abstime);
这两个函数一定要在mutex的锁定区域内使用。
调用 pthread_cond_signal() 释放被条件阻塞的线程时，如果没有任何线程基于条件变量阻塞，则调用pthread_cond_signal()不起作用。而对于 Windows，当调用 SetEvent 触发 Auto-reset 的 Event 条件时，如果没有被条件阻塞的线程，那么此函数仍然起作用，条件变量会处在触发状态。
Linux下生产者消费者问题（使用互斥锁和条件变量）:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include "pthread.h"
#define BUFFER_SIZE 16
struct prodcons
{
int buffer[BUFFER_SIZE];
pthread_mutex_t lock; //mutex ensuring exclusive access to buffer
int readpos,writepos; //position for reading and writing
pthread_cond_t notempty; //signal when buffer is not empty
pthread_cond_t notfull; //signal when buffer is not full
};
//initialize a buffer
void init(struct prodcons* b)
{
pthread_mutex_init(&b->lock,NULL);
pthread_cond_init(&b->notempty,NULL);
pthread_cond_init(&b->notfull,NULL);
b->readpos = 0;
b->writepos = 0;
}
//store an integer in the buffer
void put(struct prodcons* b, int data)
{
pthread_mutex_lock(&b->lock);
//wait until buffer is not full
while((b->writepos+1)%BUFFER_SIZE == b->readpos)
{
printf("wait for not fulln");
pthread_cond_wait(&b->notfull,&b->lock);
}
b->buffer[b->writepos] = data;
b->writepos++;
b->writepos %= BUFFER_SIZE;
pthread_cond_signal(&b->notempty); //signal buffer is not empty
pthread_mutex_unlock(&b->lock);
}
//read and remove an integer from the buffer
int get(struct prodcons* b)
{
int data;
pthread_mutex_lock(&b->lock);
//wait until buffer is not empty
