透過互斥鎖+條件量的方式實現同步與互斥

藍桉未遇釋槐鳥發表於2024-05-31
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h> // for O_CREAT and O_EXCL
#include <sys/ipc.h>
#include <sys/shm.h>
#include <errno.h>

#define SHM_SIZE 4

// 定義條件量，互斥鎖和共享記憶體
int shm_id;
pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t flag = PTHREAD_COND_INITIALIZER;

// 執行緒A
void *increment_thread(void *arg)
{
    while (1)
    {
        pthread_mutex_lock(&mut); // 上鎖
        int *buff = (int *)shmat(shm_id, NULL, 0);
        *buff = (*buff) + 1;
        int temp = *buff;
        printf("主執行緒寫入共享記憶體的值為:%d\n", buff[0]);
        shmdt(buff);
        if (temp % 3 == 0)//判斷是否滿足條件喚醒執行緒B
        {
            pthread_cond_broadcast(&flag);
        }
        pthread_mutex_unlock(&mut); // 解鎖
        sleep(1);
    }
}

// 執行緒B
void *decrement_thread(void *arg)
{
    while (1)
    {
        pthread_mutex_lock(&mut);       // 上鎖
        pthread_cond_wait(&flag, &mut); // 不滿足條件掛起
        int *buff = (int *)shmat(shm_id, NULL, 0);
        printf("\n\n滿足條件子執行緒B輸出當前i值為:%d\n\n", buff[0]);
        shmdt(buff);
        pthread_mutex_unlock(&mut); // 解鎖
    }
}

int main(int argc, char *argv[])
{
    pthread_t inc_thread, dec_thread;

    // 建立共享記憶體
    shm_id = shmget(ftok(".", 50), SHM_SIZE, IPC_CREAT | IPC_EXCL | 0644);
    // 函式呼叫失敗，原因是共享記憶體段已經存在
    if (shm_id == -1)
    {
        if (errno == EEXIST) // 此時可以再次呼叫函式開啟共享內容
        {
            shm_id = shmget(ftok(".", 50), SHM_SIZE, 0644);
        }
        else
        {
            fprintf(stderr, "shmget error,error:%d,%s\n", errno, strerror(errno));
            exit(1);
        }
    }

    // 對映共享記憶體段到程序空間中並賦予初值1
    int *buff = (int *)shmat(shm_id, NULL, 0);
    if (errno == EEXIST) // 此時可以再次呼叫函式開啟共享內容
    {
        shm_id = shmget(ftok(".", 50), SHM_SIZE, 0644);
    }
    else
    {
        fprintf(stderr, "shmget error,error:%d,%s\n", errno, strerror(errno));
        exit(1);
    }
    *buff = 1;
    shmdt(buff);

    // 建立執行緒
    if (pthread_create(&inc_thread, NULL, increment_thread, NULL) != 0)
    {
        perror("pthread_create");
        sem_unlink("/sem1");
        sem_unlink("/sem2");
        exit(EXIT_FAILURE);
    }

    if (pthread_create(&dec_thread, NULL, decrement_thread, NULL) != 0)
    {
        perror("pthread_create");
        sem_unlink("/sem1");
        sem_unlink("/sem2");
        exit(EXIT_FAILURE);
    }

    // 等待執行緒完成
    if (pthread_join(inc_thread, NULL) != 0)
    {
        perror("pthread_join");
        sem_unlink("/sem1");
        sem_unlink("/sem2");
        exit(EXIT_FAILURE);
    }

    if (pthread_join(dec_thread, NULL) != 0)
    {
        perror("pthread_join");
        sem_unlink("/sem1");
        sem_unlink("/sem2");
        exit(EXIT_FAILURE);
    }

    // 關閉共享記憶體
    shmctl(shm_id, IPC_RMID, NULL);

    printf("All threads completed successfully.\n");
    return 0;
}

參考文獻https://blog.csdn.net/daaikuaichuan/article/details/82950711

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