线程与信号量

semaphore.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <semaphore.h>
#include <pthread.h>
#include <unistd.h>

sem_t sem;

#ifdef MUTI_THREAD
void *change_resource(void *res)
{
    char *msg = (char *)res;
    printf("change_resource execute\r\n");

    while(1)
    {
        sem_wait(&sem);
        strcat(msg, "a");
        printf("resource changed with value: %s\r\n", msg);
    }
}
#endif

#ifdef SEM_POST
void do_sem_post(sem_t *p_sem)
{
    printf("do_sem_post execute\r\n");
    while(1)
    {
        sem_post(p_sem);
        sleep(2);
    }
}
#endif

int main(int argc, char *argv[])
{
    int ret = 0, val = 0, i;
    pthread_t thread;
    char resource[200] = {0};

    printf("argc is %d\r\n", argc);
    for (i = 0; i < argc; i++)
    {
        printf("argc[%d] is %s\r\n", i, argv[i]);
    }

    ret = sem_init(&sem, 0, 0);
    if (ret != 0)
    {
        printf("sem_init failed\r\n");
        return ret;
    }

    ret = sem_getvalue(&sem, &val);
    if (ret != 0)
    {
        printf("sem_getvalue failed\r\n");
        return ret;
    }
    printf("sem val is %d\r\n", val);

    ret = pthread_create(&thread, NULL, change_resource, (void *)resource);
    if (ret != 0)
    {
        printf("pthread_create failed\r\n");
        return ret;
    }
    else
    {
        printf("pthread_create success\r\n");
    }

    do_sem_post(&sem);

    ret = sem_destroy(&sem);
    if (ret != 0)
    {
        printf("sem_destroy failed\r\n");
    }

    return 0;
}

注意
(1) 子线程调用的接口函数必须是这样的格式: void *change_resource(void *)
(2) pthread_create的第一个参数要定义变量再传入地址，不可直接定义指针

makefile

ROOT:=/repo/ezheson/test_dm/semaphore
FLAG=-lpthread
OBJECTS=$(ROOT)/build/semaphore.o
DEFINES=-D MUTI_THREAD \
        -D SEM_POST

$(ROOT)/build/semaphore:$(OBJECTS)
 $(CC) $(FLAG) $^ -o $@
$(OBJECTS):$(ROOT)/build/%.o:$(ROOT)/%.c
 $(CC) $(DEFINES) -c $< -o $@

.PHONY:clean
clean:
 cd ./build; rm -rf *

注意
(1) 使用sem_时，编译时要使用库-lpthread, 在连接时使用
(2) 使用-D定义宏，在编译时使用

运行结果：