C 调用 semget 返回错误 "semget: No such file or directory"

Question

我是一个 C 菜鸟，正在尝试创建一个使用 semget 的程序(首先是 main.c 的 if 语句)。我在 linux 机器上工作并编写了一些涉及信号量的代码。当我运行我的程序时，它返回“semget:没有这样的文件或目录”。我没有包括 carbon.c 和 hydrogen.c 文件，但如果有人认为他们对问题有必要，我会把它们放上来。感谢您的帮助。

主.c

#include "main.h"

void hydrogen(void);//executes hydrogen.c
void carbon(void);//executes carbon.c

int main() {
    int semid, shmid;//semaphore memory id, shared memory id
    unsigned short seminit[NUM_SEMS];//used to initialize semaphores
    struct common *shared;//pointer to shared data structure
    union semun semctlarg;//used to initialize semaphores

    //get semaphore memory id
    if ((semid = semget(SEMKEY, NUM_SEMS, 0777)) < 0) {
        perror("semget");
        exit(EXIT_FAILURE);
    }

    seminit[MUTEX] = 1;//initialize mutex semaphore count to 1
    seminit[SH] = 0;//initialize hyrdrogen semaphore count to 0
    seminit[SC] = 0;//initialize carbon semaphore count to 0
    semctlarg.array = seminit;//set control array

    //apply initialization
    if ((semctl(semid, NUM_SEMS, SETALL, semctlarg)) < 0) {
        perror("semctl");
        exit(EXIT_FAILURE);
    }

    //get shared memory id
    if ((shmid = shmget(SHMKEY, 1*K, 0777)) < 0) {
        perror("shmget");
        exit(EXIT_FAILURE);
    }

    //retrieve pointer to shared data structure
    if ((shared = (struct common *)shmat(shmid, 0, 0)) < 0) {
        perror("shmat");
        exit(EXIT_FAILURE);
    }

    //initialize shared data structure variables
    shared->waiting_H = 0;
    shared->waiting_C = 0;

    int retVal;//used to check return value of fork()

    // spawn 20 Hydrogens
    for (int i=0; i<NUM_H; i++) {
        if ((retVal = fork()) == 0) {
            hydrogen();
            fflush(stdout);
            printf("New Hydrogen process created\n");
            fflush(stdout);
        } else if (retVal < 0) {
            perror("fork");
            exit(EXIT_FAILURE);
        }
    }

    // spawn 5 Carbons
    for (int i=0; i<NUM_C; i++) {
        if ((retVal = fork()) == 0) {
            carbon();
            fflush(stdout);
            printf("New Hydrogen process created\n");
            fflush(stdout);
        } else if (retVal < 0) {
            perror("fork");
            exit(EXIT_FAILURE);
        }
    }

    //wait for all car processes to finish
    for (int i = 0; i < 25; ++i) {
        if (wait(0) < 0) {
            perror("wait");
            exit(EXIT_FAILURE);
        }
    }

    printf("All atoms have crossed!\n");

        //delete semaphores
    if (semctl(semid, NUM_SEMS, IPC_RMID, 0) < 0) {
        perror("semctl");
        exit(EXIT_FAILURE);
    }

    //delete shared memory
    if (shmctl(shmid, IPC_RMID, 0) < 0) {
        perror("shmctl");
        exit(EXIT_FAILURE);
    }

    return EXIT_SUCCESS;
}

void carbon(void) {
    execl("carbon", "carbon", 0);
    perror("execl");
    exit(EXIT_FAILURE);//if exec returns there was an error
}

void hydrogen(void) {
    execl("hydrogen", "hydrogen", 0);
    perror("execl");
    exit(EXIT_FAILURE);//if exec returns there was an error
}

主.h

#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>
#include <sys/errno.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>

#define SEMKEY 77
#define SHMKEY 77

#define NUM_SEMS    3
#define MUTEX       0
#define SH  1
#define SC  2

#define NUM_C   5
#define NUM_H   20

#define K 1024//used for shared memory creation

enum MoleculeName { Carbon, Hydrogen };

//used to initialize semaphores
union semun {
    unsigned short *array;
};

//shared data structure among processes
struct common {
    int waiting_C;
    int waiting_H;
};

void semWait(int semid, int semaphore) {
    struct sembuf psembuf;

    psembuf.sem_op = -1;
    psembuf.sem_flg = 0;
    psembuf.sem_num = semaphore;
    semop(semid,&psembuf,1);
    return;
}

void semSignal(int semid, int semaphore) {
    struct sembuf vsembuf;

    vsembuf.sem_op = 1;
    vsembuf.sem_flg = 0;
    vsembuf.sem_num = semaphore;
    semop(semid,&vsembuf,1);
    return;
}

Answer 1

使用

semid = semget(SEMKEY, NUM_SEMS, IPC_CREAT|0777。

如果不存在，它将创建信号量。