互相独立进程间共享内存互斥访问的解决办法

//processA.c文件
#include <stdlib.h>
#include <stdio.h>
#include <sys/shm.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <errno.h>
#include <pthread.h>
 
#define BUF_SIZE 4096
 
int main()
{
    void *shm_addr = NULL;
    char buffer[BUF_SIZE];
	pthread_mutex_t * sharedLock;
	pthread_mutexattr_t ma;
 
    int shmid;
    // 使用约定的键值创建共享内存
    shmid = shmget((key_t) 1234,  BUF_SIZE, 0666 | IPC_CREAT);
    printf("shmid : %u\n", shmid);
    if (shmid < 0)
    {
        perror("shmget error!");
        exit(1);
    }
 
    // 将共享内存附加到本进程
    shm_addr = shmat(shmid, NULL, 0);
    if (shm_addr == (void *) -1)
    {
        perror("shmat error!&