note

使用信号量进行进程间通信时，信号量要放置在共享内存上；若是线程间通信，放堆上或全局变量区就行

code

// 使用信号量进行进程间通信时，信号量要放置在共享内存上；若是线程间通信，放堆上或全局变量区就行

#include <semaphore.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/mman.h>
#include <fcntl.h>

const char* shm_obj1 = "shm1";
const char* shm_obj2 = "shm2";
int shm_id1 = -1;
int shm_id2 = -1;
void* shm_handle1 = NULL;	// 对应生产量
void* shm_handle2 = NULL;	// 对应容纳量
sem_t* sem_cnt = NULL;  // 已生产量
sem_t* sem_capcity = NULL; // 可容纳量
const int sem_between_threads = 0;  // 线程间通信
const int sem_between_processes = 1;    // 进程间通信

// 父进程负责生产
void parent_work(void) {
    int ret = -1;
    int val = 0;
    int i = 0;
    
	for (i = 0; i < 10; i++) {
        ret = sem_wait(sem_capcity);
        if (ret == -1) {
            fprintf(stderr, "parent process sem_wait error,%s\n", strerror(errno));
        }
        else if (ret == 0) {
            (void)sem_getvalue(sem_capcity, &val);
            fprintf(stdout, "parent process get sem_capcity value:%d\n", val);
            (void)sem_post(sem_cnt);
        }
        sleep(2);
    }
	

    wait(NULL);
    (void)sem_destroy(sem_cnt);
    (void)sem_destroy(sem_capcity);
	(void)shm_unlink(shm_obj1);
	(void)shm_unlink(shm_obj2);
    exit(EXIT_SUCCESS);
}

// 子进程负责消费
void child_work(void) {
    int ret = -1;
    int val = 0;
    int i = 0;
    for (i = 0; i < 10; i++) {
        ret = sem_wait(sem_cnt);
        if (ret == -1) {
            fprintf(stderr, "child process sem_wait error,%s\n", strerror(errno));
        }
        else if (ret == 0) {
            (void)sem_getvalue(sem_cnt, &val);
            fprintf(stdout, "child process get sem_cnt value:%d\n", val);
            (void)sem_post(sem_capcity);
        }
        sleep(1);
    }
    exit(EXIT_SUCCESS);
}

int main(int argc, char** argv) {
    int ret = -1;
    pid_t pid = 0;

	shm_id1 = shm_open(shm_obj1, O_CREAT|O_RDWR, 666);
	if (shm_id1 == -1) {
		fprintf(stderr, "parent process shm_open shm_obj1 error,%s\n", strerror(errno));
		exit(EXIT_FAILURE);
	}

	shm_id2 = shm_open(shm_obj2, O_CREAT|O_RDWR, 666);
	if (shm_id1 == -1) {
		fprintf(stderr, "parent process shm_open shm_obj2 error,%s\n", strerror(errno));
		(void)shm_unlink(shm_obj1);
		exit(EXIT_FAILURE);
	}

	ftruncate(shm_id1, sizeof(sem_t));
	ftruncate(shm_id2, sizeof(sem_t));

	shm_handle1 = mmap(NULL, sizeof(sem_t), PROT_READ|PROT_WRITE, MAP_SHARED, shm_id1, 0);
	if (shm_handle1 == MAP_FAILED) {
		fprintf(stderr, "parent process mmap shm_id1 error,%s\n", strerror(errno));
		(void)shm_unlink(shm_obj1);
		(void)shm_unlink(shm_obj2);
		exit(EXIT_FAILURE);
	}
	
	shm_handle2 = mmap(NULL, sizeof(sem_t), PROT_READ|PROT_WRITE, MAP_SHARED, shm_id2, 0);
	if (shm_handle2 == MAP_FAILED) {
		fprintf(stderr, "parent process mmap shm_id2 error,%s\n", strerror(errno));
		(void)shm_unlink(shm_obj1);
		(void)shm_unlink(shm_obj2);
		exit(EXIT_FAILURE);
	}

	sem_cnt = shm_handle1;
	sem_capcity = shm_handle2;

    // 可存储量初始化为10
    ret = sem_init(sem_capcity, sem_between_processes, 10);
    if (ret == -1) {
        fprintf(stderr, "parent process sem_init sem_capcity error,%s\n", strerror(errno));
		(void)shm_unlink(shm_obj1);
		(void)shm_unlink(shm_obj2);
        exit(EXIT_FAILURE);
    }

    // 已生产量初始化为0
    ret = sem_init(sem_cnt, sem_between_processes, 0);
    if (ret == -1) {
        fprintf(stderr, "parent process sem_init sem_cnt error,%s\n", strerror(errno));
        (void)sem_destroy(sem_capcity);
		(void)shm_unlink(shm_obj1);
		(void)shm_unlink(shm_obj2);
        exit(EXIT_FAILURE);
    }

    pid = fork();
    if (pid < 0) {
        fprintf(stderr, "parent process fork error,%s\n", strerror(errno));
        (void)sem_destroy(sem_cnt);
        (void)sem_destroy(sem_capcity);
		(void)shm_unlink(shm_obj1);
		(void)shm_unlink(shm_obj2);
        exit(EXIT_FAILURE);
    }

    if (pid > 0) {
        fprintf(stdout, "i am parent process,pid:%d\n",getpid());
        parent_work();
    }
    else if (pid == 0) {
        fprintf(stdout, "i am child process,pid:%d\n",getpid());
        child_work();
    }

    return 0;
}


// sem_init\sem_destroy

test