c - 如何将 2 个进程“转换”为父子进程？

Question

所以我有这个很棒的代码，用于以前Ali Hasan Ahmed Khan的死锁的 C 示例。我只是在考虑将其转换为父子进程，因此以某种方式使 funcA 成为父进程，然后分叉 funcB。当我使用 fork 命令时，我在 main 中遇到了一个错误，说 funcB 不存在。这可以转换吗？完整的代码是：

#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/sem.h>

#define PERMS 0660

int semId;

int initSem(int semId, int semNum, int initValue) {
    return semctl(semId, semNum, SETVAL, initValue);
}

// Try to take a resource, wait if not available
int P(int semId, int semNum) {
    struct sembuf operationList[1];
    operationList[0].sem_num = semNum;
    operationList[0].sem_op = -1;
    operationList[0].sem_flg = 0;
    return semop(semId, operationList, 1);
}

// Release a resource
int V(int semId, int semNum) {
    struct sembuf operationList[1];
    operationList[0].sem_num = semNum;
    operationList[0].sem_op = 1;
    operationList[0].sem_flg = 0;

    return semop(semId, operationList, 1);
}

void* funcA(void* nothing) {
    printf("Thread A try to lock 0...\n");
    P(semId, 0);        // Take resource/semaphore 0     of semID
    printf("Thread A locked 0.\n");

    usleep(50*1000);  // Wait 50 ms

    printf("Thread A try to lock 1...\n");
    P(semId, 1);        // Take resource/semaphore 1 of semID
    printf("Thread A locked 1.\n");

    V(semId, 0);        // Release resource/semaphore 0 of semID
    V(semId, 1);        // Release resource/semaphore 1 of semID
    return NULL;
}

void* funcB(void* nothing) {
    printf("Thread B try to lock 1...\n");
    P(semId, 1);
    printf("Thread B locked 1.\n");

    usleep(5*1000);

    printf("Thread B try to lock 0...\n");
    P(semId, 0);
    printf("Thread B locked 0.\n");

    V(semId, 0);
    V(semId, 1);
    return NULL;
}

int main(int argc, char* argv[]) {
    int i;

    // ftok generates a key based on the program name and a char value
semId = semget(ftok(argv[0], 'A'), 2, IPC_CREAT | PERMS);

initSem(semId, 0, 1);
initSem(semId, 1, 1);

pthread_t thread[2];

pthread_create(&thread[0], NULL, funcA, NULL);
pthread_create(&thread[1], NULL, funcB, NULL);

for (i = 0 ; i < 2 ; i++) {
    pthread_join(thread[i], NULL);
}
printf("This is not printed in case of deadlock\n");
semctl(semId, 0, IPC_RMID, 0);
semctl(semId, 1, IPC_RMID, 0);
return 0;
}

标签： cparent-child