Linux多线程编程

核心提示：(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,

(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);
一定要在mutex的锁定区域内使用。

使用条件变量实现“生产者消费者问题”:
#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 full\n");
pthread_cond_wait(&b->notfull,&b->lock);
}

b->buffer[b->writepos]=data;
b->writepos++;
pthread_cond_signal(&b->notempty); //signal buffer is not empty
pthread_mutex_unlock(&b->lock);
}

//read and remove an integer from the buffer
void get(struct prodcons* b)
{
int data;
pthread_mutex_lock(&b->lock);
//wait until buffer is not empty
while(b->writepos==b->readpos)
{
printf("wait for not empty\n");
pthread_cond_wait(&b->notempty,&b->lock);
}

data=b->buffer[b->readpos];
b->readpos++;
if(b->readpos>=BUFFER_SIZE) b->readpos=0;
pthread_cond_signal(&b->notfull); //signal buffer is not full
pthread_mutex_unlock(&b->lock);
return data;
}

#define OVER -1

struct prodcons buffer;

void * producer(void * data)
{
int n;
for(n=0;n<1000;++n)
{
printf("put-->%d\n",n);
put(&buffer,n);
}
put(&buffer,OVER);
printf("producer stopped\n");
return NULL;
}

void * consumer(void * data)
{
int n;