多线程传参问题

多线程传参，分为两种方式。一种是设置 ==全局变量==；另一种是通过int pthread_create（（pthread_t *thread, pthread_attr_t *attr, void *（*start_routine）（void *）, void *arg）函数的最后一项参数传参，通过pthread_create 参数传参要注意，其参数类型为（void *）。

设置全局变量时，应该注意加上同步机制，例如如p v操作或者锁机制。避免多线程访问同一资源时发生竞争。如果线程个数可以确定，线程间是同步进行的，则线程间的私有资源(线程间使用的buffer，变量）不需要加锁，这种情况一般是设置全局标志来使线程同步。

函数传参时，避免主程序因为等待线程而阻塞，使用pthread_detach(pid)函数使线程函数自运行。则该线程运行结束后会自动释放所有资源。使用函数传参时，注意以下几个易错点：
 1. 传递的参数类型是个（void型）指针。
 2. 参数传递中，不能使用局部变量int a， 以&a 的方式传参。可采用

int a = 5;//局部变量
pthread_create（pid,  NULL,  thread_func,  (void  *)a）;
........
void *thread_func(void *argc)
{
    ......
       b = (int )argc;//实现局部变量的对线程函数的传参
    ......
}

函数传参例子

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

#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>

#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <unistd.h>


void *thread1_func(void *argc)
{
    int ret;
    int iSocket =(int )argc;
    
    char heartSendBuf[14] = {'\0'};
    
    while(1) {
    
        ret = send(iSocket, heartSendBuf, 14, 0);
        if (ret < 0){
            perror("thread1_func:");
            close(iSocket);
            pthread_exit(NULL); 
        }
        
        printf("the heart send to client ok!\n");
    
    }
    
}

void *thread2_func(void *argc)
{
    int ret;
    int iSocket =(int )argc;
    
    char heartRecvBuf[14] = {'1'};
    sleep(4);
    while(1) {
    
        ret = recv(iSocket, heartRecvBuf, 14, 0);
        if (ret < 0){
            perror("thread2_func:");
//          close(iSocket);
            pthread_exit(NULL); 
        }
        
        printf("the heart recv from client ok!\n");
    
    }
    
}

#define SERVER_IP "127.0.0.1"

static unsigned short tmp_port = 8803;
int start_server(void)
{
    int iSocket;
    int nZero = 0;
    
    struct timeval t = {20, 0};
    struct sockaddr_in myserver_addr;
    struct sockaddr_in client_addr;
    
    socklen_t addrlen = sizeof(myserver_addr);
    memset(&myserver_addr, 0, sizeof(myserver_addr));
    myserver_addr.sin_family = AF_INET;
    myserver_addr.sin_port = htons(tmp_port);
    myserver_addr.sin_addr.s_addr = inet_addr("192.168.0.18");
    
    memset(&client_addr, 0, sizeof(client_addr));
    client_addr.sin_family = AF_INET;
    client_addr.sin_port = htons(8802);
    client_addr.sin_addr.s_addr = inet_addr("192.168.0.20");
    
    if ((iSocket = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ){
        perror("Create Socket failed: ");
        exit(1);
    }
    
    if (bind(iSocket, (struct sockaddr *)&myserver_addr, sizeof(myserver_addr))== -1){
        perror("bind error");

    }else {
        printf("bind ok\n");
    }
    
    if (connect(iSocket, (struct sockaddr *)&client_addr, addrlen) != 0){
        perror("connect error");
        return -1;
    }else {
        printf("connect ok\n");
    }
    
    if (setsockopt(iSocket, SOL_SOCKET, SO_SNDBUF, (char *)&nZero, sizeof(nZero)) < 0){
        perror("thread_send:setsockopt heartSendBuf error");
        return -1;
    }
    
    if (setsockopt(iSocket, SOL_SOCKET, SO_RCVTIMEO, &t, sizeof(t)) < 0){
        perror("thread_recv:setsockopt error");
        return -1;
     }
     return iSocket;
}

int main(int argc, char **argv)
{
    int ret;
    int iSocket;
    
    pthread_t pid1,pid2;
    
    //create client
    iSocket = start_server();
    if (iSocket < 0){
        perror("create client server error");
        return -1;
    }

    ret = pthread_create(&pid1, NULL, thread1_func, (void *)iSocket);
    if (ret < 0){
        perror("create thread_caller error");
        return -1;
    }else {
        printf(" create heart send thread ok\n");
    }
    pthread_detach(pid1);
    
    ret = pthread_create(&pid2, NULL, thread2_func, (void *)iSocket);
    if (ret < 0){
        perror("create thread_caller error");
        return -1;
    }else {
        printf(" create heart send thread ok\n");
    }
    pthread_detach(pid2);
    
    while(1);
    
}

总结

    多线程传参，传参的值是（void *）类型，属于地址传参。在传入多个值时应当使用结构体封装。当使局部变量时，注意提前释放局部变量资源，生命周期应该等待线程结束。