多線程傳參

  多線程傳參，分爲兩種方式。一種是設置 ==全局變量==；另一種是通過int pthread_create（（pthread_t *thread, pthread_attr_t *attr, void *（*start_routine）（void *）, void *arg）函數的最後一項參數傳參，通過pthread_create 參數傳參要注意，其參數類型爲（void *）。

設置全局變量時，應該注意加上同步機制，例如如p v操作或者鎖機制。避免多線程訪問同一資源時發生競爭。如果線程個數可以確定，線程間是同步進行的，則線程間的私有資源(線程間使用的buffer，變量）不需要加鎖，這種情況一般是設置全局標誌來使線程同步。

函數傳參時，避免主程序因爲等待線程而阻塞，使用pthread_detach(pid)函數使線程函數自運行。則該線程運行結束後會自動釋放所有資源。使用函數傳參時，注意以下幾個易錯點：
 1. 傳遞的參數類型是個（void型）指針。
 2. 參數傳遞中，不能使用局部變量int a， 以&a 的方式傳參。可採用

int a = 5;//局部變量
pthread_create（pid,  NULL,  thread_func,  (void  *)a）;
........
void *thread_func(void *argc)
{
    ......
       b = (int )argc;//實現局部變量的對線程函數的傳參
    ......
}

函數傳參例子

#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);

}

總結

    多線程傳參，傳參的值是（void *）類型，屬於地址傳參。在傳入多個值時應當使用結構體封裝。當使局部變量時，注意提前釋放局部變量資源，生命週期應該等待線程結束。