linux内核中的条件变量,linux 条件变量

内涵：和一个普通互斥体结合使用的一块资源。包括了变量本身、正在等待的线程信息等。

初始化： pthread_cond_t cond = PTHREAD_COND_ININTIALIZER;

销毁:   pthread_cond_destroy(pthread_cond_t*);

等待和发送信号：

假设：有一个房间，钥匙是mutex，一开始门是开着的。 房间内有一个电话cond，包括所有在上面已经登记过的电话号码(线程id)

1. pthread_mutex_lock(&mutex);

2. pthread_cond_wait(&cond, &mutex);

// do sth

3. pthread_mutex_unlock(&mutex);

过程： 第1步，来了一个人小张(线程)，先进房间并且锁上门，不让其他人同时进来。第2步，小张把自己的电话号码登记在了电话上。然后小张就打开锁出来了并且倒地就睡一直等到有人打电话给他，因为他要等其他人做完了一些事情之后打电话通知他以便它继续做。第3步，有人打电话给小张了，小张又进入房间并且锁上门，干他自己分内的事情了。。。

phtread_cond_signal(&cond);按照某些规则挑一个电话号码(比如优先级高低)通知那个人(线程)

下面是我写的一个 用条件变量实现join所有线程的例子

#include "../common.h"       //常用的unix头文件，自己写

#include "netdb.h"

#include "pthread.h"

struct client_info {

int tid;

int is_end;

};

struct client_info ci[20];

int ndone = 0;

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

pthread_cond_t  cond = PTHREAD_COND_INITIALIZER;

class  client_reply {

public:

int tid;

char* msg;

};

void* client_work(void* arg) {

printf("thread %d start...n", pthread_self());

int sockfd  = *((int*)arg);

char buf[1024];

for(;;) {

int n  = read(sockfd, buf, sizeof(buf));

if(n == 0)break;

if(n == -1)break;

buf[n] = 0;

printf("thread %d read %d bytes:%sn", pthread_self(), n, buf);

}

client_reply* p = new client_reply;

p->msg = "oh baby";

p->tid = pthread_self();

pthread_mutex_lock(&mutex);

ndone++;

int i;

for(i=0; i<20; i++) {

if(ci[i].tid == 0) {

ci[i].tid = pthread_self();

ci[i].is_end = 1;

break;

}

}

printf("thread %d end...n", pthread_self());

//      printf("c[%d].tid = %dtc[%d].is_end = %dt ndone=%dn", i, ci[i].tid, i, ci[i].is_end, ndone);

pthread_mutex_unlock(&mutex);

pthread_cond_signal(&cond);

return p;

}

void* client_wait(void* arg) {

printf("thread %d client wait start...n", pthread_self());

for(;;) {

pthread_mutex_lock(&mutex);

while(ndone == 0) {

printf("cleint wait ....n");

pthread_cond_wait(&cond, &mutex);

}

for(int i=0; i<20; i++) {

if(ci[i].is_end == 1) {

struct client_reply *reply;

pthread_join(ci[i].tid, (void**)&reply);

ndone--;

printf("pthread_join tid:%d msg:%sn", reply->tid, reply->msg);

memset(&ci[i], 0, sizeof(struct client_info));

}

}

pthread_mutex_unlock(&mutex);

}

return 0;

}

int main(int argc, char** argv) {

memset(ci, 0, sizeof(struct client_info)*20);

char* ip = NULL;

char* port = "8888";

if(argc > 1)ip = argv[1];

if(argc > 2)port = argv[2];

struct addrinfo *res;

struct addrinfo hints;

memset(&hints, 0, sizeof(hints));

hints.ai_flags = AI_PASSIVE;

hints.ai_family = AF_INET;

hints.ai_socktype = SOCK_STREAM;

int n = getaddrinfo(ip, port, &hints, &res);

if(n != 0)perror("getaddrinfo error");

int sockfd = socket(res->ai_family, res->ai_socktype, res->ai_protocol);

if(sockfd == -1)perror("socket error");

n = bind(sockfd, res->ai_addr, res->ai_addrlen);

if(n == -1)perror("bind error");

n = listen(sockfd, 5);

if(n == -1)perror("listen error");

char buf[1024];

inet_ntop(AF_INET, &(((struct sockaddr_in*)res->ai_addr)->sin_addr), buf, sizeof(buf));

printf("serer is started in [%s]:[%d]n", buf, ntohs(((struct sockaddr_in*)res->ai_addr)->sin_port));

//create a thread to recive client trhead

pthread_t tid;

pthread_create(&tid, 0, client_wait, 0);

for(;;) {

struct sockaddr_in client_addr;

socklen_t client_addr_len = sizeof(client_addr);

int clientfd = accept(sockfd, (struct sockaddr*)&client_addr, &client_addr_len);

if(clientfd == -1) {

perror("accept error");

continue;

}

pthread_t tid;

int n = pthread_create(&tid, 0, client_work, &clientfd);

if(n != 0)printf("pthread_create errorn");

}

return 0;

}