執行緒相比於程序具有如下優點:

1.執行緒的建立和上下文切換比程序的建立和上下文切換要快.上下文切換時不需要切換資料區和堆.

2.執行緒間交換資料時無需特殊技術.可以利用資料區和堆交換資料.

執行緒同步(兩方面)

1.同時訪問同一記憶體空間時發生的情況.

2.需要指定訪問同一記憶體空間的執行緒執行順序的情況.

訊號量示例(控制訪問順序的同步)

示例場景:

                執行緒A從使用者輸入得到值後存入全域性變數num,此時執行緒B將取走該值並累加.該過程共執行5次,完成後輸出總和並退出程式.

#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>

void * read(void * arg);
void * accu(void * arg);
static sem_t sem_one;
static sem_t sem_two;
static int num;


int main(int argc, char *argv[])
{
    pthread_t id_t1, id_t2;
    sem_init(&sem_one, 0, 0);
    sem_init(&sem_two, 0, 1);

    pthread_create(&id_t1, NULL, read, NULL);
    pthread_create(&id_t2, NULL, accu, NULL);

    pthread_join(id_t1, NULL);
    pthread_join(id_t2, NULL);

    sem_destroy(&sem_one);
    sem_destroy(&sem_two);

    return 0;
}

void * read(void * arg)
{
    int i;
    for (i = 0; i < 5; i++) {
        fputs("Input num: ", stdout);
        sem_wait(&sem_two);
        scanf("%d", &num);
        sem_post(&sem_one);
    }
    return NULL;
}

void * accu(void * arg)
{
    int sum = 0 , i;
    for (i = 0; i < 5; i++) {
        sem_wait(&sem_one);
        sum+= num;
        sem_post(&sem_two);
    }
    printf("Result: %d \n", sum);
    return NULL;
}
 

銷燬執行緒的方法:

1.呼叫pthread_join函式.會引起呼叫該函式的執行緒阻塞.

2.呼叫pthread_detach函式.不會阻塞,在終止的同時銷燬相應的執行緒.

多執行緒併發伺服器端的實現

伺服器端:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <pthread.h>

#define BUF_SIZE 100
#define MAX_CLNT 256

void * handle_clnt(void * arg);
void send_msg(char *msg, int len);
void error_handling(char * msg);
int clnt_cnt = 0;
int clnt_socks[MAX_CLNT];
pthread_mutex_t mutx;

int main(int argc, char *argv[])
{
    int serv_sock, clnt_sock;
    struct sockaddr_in serv_adr, clnt_adr;
    socklen_t clnt_adr_sz;
    pthread_t t_id;
    if (argc != 2) {
        printf("Usage : %s <port> \n", argv[0]);
        exit(1);
    }

    //建立互斥量
    pthread_mutex_init(&mutx, NULL);
    serv_sock = socket(PF_INET, SOCK_STREAM, 0);

    memset(&serv_adr, 0, sizeof(serv_adr));
    serv_adr.sin_family = AF_INET;
    serv_adr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_adr.sin_port = htons(atoi(argv[1]));

    if(bind(serv_sock, (struct sockaddr *) &serv_adr, sizeof(serv_adr)) == -1)
        error_handling("bind() error");
    if(listen(serv_sock, 5) == -1)
        error_handling("listen() error");

    while (1)
    {
        clnt_adr_sz = sizeof(clnt_adr);
        clnt_sock = accept(serv_sock, (struct sockaddr*)&clnt_adr, &clnt_adr_sz); //阻斷，監聽客服端連線請求

        //臨界區
        pthread_mutex_lock(&mutx); //加鎖
        clnt_socks[clnt_cnt++] = clnt_sock; //新連線的客服端儲存到clnt_socks數組裡
        pthread_mutex_unlock(&mutx); //釋放鎖

        //建立執行緒
        pthread_create(&t_id, NULL, handle_clnt, (void*) &clnt_sock);
        pthread_detach(t_id); //銷燬執行緒，執行緒return後自動呼叫銷燬，不阻斷

        printf("Connected client IP: %s \n", inet_ntoa(clnt_adr.sin_addr));
    }

    close(serv_sock);
    return 0;
}

//執行緒執行
void * handle_clnt(void * arg)
{
    int clnt_sock = *((int *)arg);
    int str_len = 0, i;
    char msg[BUF_SIZE];

    while ((str_len = read(clnt_sock, msg, sizeof(msg))) != 0)
        send_msg(msg, str_len);

    //從陣列中移除當前客服端
    pthread_mutex_lock(&mutx);
    for (i = 0; i < clnt_cnt; i++)
    {
        if (clnt_sock == clnt_socks[i])
        {
            while (i++ < clnt_cnt - 1)
                clnt_socks[i] = clnt_socks[i + 1];
            break;
        }
    }
    clnt_cnt--;
    pthread_mutex_unlock(&mutx);
    close(clnt_sock);
    return NULL;
}

//向所有連線的客服端傳送訊息
void send_msg(char * msg, int len)
{
    int i;
    pthread_mutex_lock(&mutx);
    for (i = 0; i < clnt_cnt; i++)
        write(clnt_socks[i], msg, len);
    pthread_mutex_unlock(&mutx);
}

void error_handling(char *message)
{
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}
 

客戶端:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <pthread.h>

#define BUF_SIZE 100
#define NAME_SIZE 20

void * send_msg(void * arg);
void * recv_msg(void * arg);
void error_handling(char *message);

char name[NAME_SIZE] = "[DEFAULT]";
char msg[BUF_SIZE];

int main(int argc, const char * argv[]) {
    int sock;
    struct sockaddr_in serv_addr;
    pthread_t snd_thread, rcv_thread;
    void * thread_return;

    if(argc != 4)
    {
        printf("Usage: %s <IP> <port> name \n", argv[0]);
        exit(1);
    }

    sprintf(name, "[%s]", argv[3]); //聊天人名字，配置到編譯器引數裡
    sock = socket(PF_INET, SOCK_STREAM, 0);
    if(sock == -1)
        error_handling("socket() error");

    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = inet_addr(argv[1]);
    serv_addr.sin_port = htons(atoi(argv[2]));

    if (connect(sock, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) == -1)
        error_handling("connect() error");

    //多執行緒分離輸入和輸出
    pthread_create(&snd_thread, NULL, send_msg, (void *)&sock);
    pthread_create(&rcv_thread, NULL, recv_msg, (void *)&sock);
    //阻塞，等待返回
    pthread_join(snd_thread, &thread_return);
    pthread_join(rcv_thread, &thread_return);

    close(sock);
    return 0;
}

//傳送訊息
void * send_msg(void * arg)
{
    int sock = *((int *)arg);
    char name_msg[NAME_SIZE + BUF_SIZE];
    while (1) {
        fgets(msg, BUF_SIZE, stdin);
        if (!strcmp(msg, "q\n") || !strcmp(msg, "Q \n")) {
            close(sock);
            exit(0);
        }
        sprintf(name_msg, "%s  %s", name, msg);
        write(sock, name_msg, strlen(name_msg));
    }
    return NULL;
}

//接收訊息
void * recv_msg(void * arg)
{
    int sock = *((int *)arg);
    char name_msg[NAME_SIZE + BUF_SIZE];
    int str_len;
    while (1) {
        str_len = read(sock, name_msg, NAME_SIZE + BUF_SIZE - 1);
        if(str_len == -1)
            return (void *)-1;
        name_msg[str_len] = 0;
        fputs(name_msg, stdout);
    }
    return NULL;
}

void error_handling(char *message)
{
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}