线程间通讯的信号量semaphore.h

 sem_init 

SEM_INIT(3)                                                                               Linux Programmer's Manual                                                                              SEM_INIT(3)

NAME
       sem_init - initialize an unnamed semaphore

SYNOPSIS
       #include <semaphore.h>

       int sem_init(sem_t *sem, int pshared, unsigned int value);

       Link with -pthread.

 sem_wait

NAME
       sem_wait, sem_timedwait, sem_trywait - lock a semaphore

SYNOPSIS
       #include <semaphore.h>

       int sem_wait(sem_t *sem);

       int sem_trywait(sem_t *sem);

       int sem_timedwait(sem_t *sem, const struct timespec *abs_timeout);

       Link with -pthread.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       sem_timedwait(): _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600

            struct timespec {
               time_t tv_sec;      /* Seconds */
               long   tv_nsec;     /* Nanoseconds [0 .. 999999999] */
           };

sem_post 函数 

NAME
       sem_post - unlock a semaphore

SYNOPSIS
       #include <semaphore.h>

       int sem_post(sem_t *sem);

       Link with -pthread.

综合测试代码 

测试代码：

验证项目：

1 signal是进程级别的

2 sem_t和发送和等待

3 线程传递结构体参数

4 发送一个signal

5 线程的分离

#include <stdio.h>
#include <iostream>
#include <pthread.h>
#include <unistd.h>
#include <string.h>
#include <semaphore.h>
#include <signal.h>
#include <map>

#define DEBUG_INFO(format, ...) printf("%s:%d -- " format "\n", __func__, __LINE__,##__VA_ARGS__)

typedef void (*sighandler)(int signo);
std::map<pthread_t ,std::string> thread_map;
void sig_func(int signo) {
    switch(signo) {
        case SIGUSR1:
            DEBUG_INFO("SIGUSR1 signal %u,%lu",getpid(),pthread_self());
            std::cout << __func__ << " " << thread_map[pthread_self()] << std::endl;
            break;
        default:
            DEBUG_INFO("unkonwn signo = %d\n", signo);
            break;
    }
}

struct mystruct{
    pthread_t thread_id;
    sem_t sem;
    char buf[1024];
    int fd;
    int socket;
    int arg1;
    int arg2;
};

void* func(void *arg){
    struct mystruct *pms = (struct mystruct*)arg;
    pthread_detach(pthread_self());
    signal(SIGUSR1,sig_func);
    DEBUG_INFO("pthread_self = %lu\n", pthread_self());
    DEBUG_INFO("wait a semaphore");
    sem_wait(&pms->sem);
    std::cout << thread_map[pthread_self()] << std::endl;
    DEBUG_INFO("get a semaphore thread_id = %lu",pms->thread_id);
    DEBUG_INFO("thread pid = %u",getpid());
    while(1){
        //process(fd)
        //process(socket)
        usleep(1);
    }
}

int main(int argc, char **argv){
    std::cout << "Usage: " << argv[0] << std::endl;
    DEBUG_INFO("main pid = %u",getpid());
    DEBUG_INFO("%ld",sizeof(pthread_t));
    DEBUG_INFO("main thread = %lu\n", pthread_self());
    thread_map[pthread_self()] = std::string("main thread");
    std::cout << __func__ << " " << thread_map[pthread_self()] << std::endl;
    for(int i = 0; i < 3;i++){
        struct mystruct *pms = (struct mystruct*)malloc(sizeof(struct mystruct));
        
        if(pms == NULL){
            perror("malloc");
            exit(-1);
        }
        sem_init(&pms->sem,0,0);
        pthread_t t;
        int ret = pthread_create(&t,NULL,func,pms);
        if(ret != 0){
            perror("pthread_create");
            exit(1);
        }
        thread_map[pthread_self()] = std::string("child thread:") + std::to_string(i);
        pms->thread_id = t;
        sleep(1);
        sem_post(&pms->sem);
    }
    kill(getpid(),SIGUSR1);
    kill(getpid(),SIGUSR1);
    kill(getpid(),SIGUSR1);
    kill(getpid(),SIGUSR1);
    kill(getpid(),SIGUSR1);
    while(1){
        sleep(1);
    }
    DEBUG_INFO("bye bye");
    return 0;
}

执行结果：

main:55 -- main pid = 24855
main:56 -- 8
main:57 -- main thread = 139649254037312

main main thread
func:40 -- pthread_self = 139649236711168

func:41 -- wait a semaphore

func:44 -- get a semaphore thread_id = 139649236711168
func:45 -- thread pid = 24855
func:40 -- pthread_self = 139649228318464

func:41 -- wait a semaphore

func:44 -- get a semaphore thread_id = 139649228318464
func:45 -- thread pid = 24855
func:40 -- pthread_self = 139649219925760

func:41 -- wait a semaphore
sig_func:17 -- SIGUSR1 signal 24855,139649254037312
sig_func child thread:2
sig_func:17 -- SIGUSR1 signal 24855,139649254037312
sig_func child thread:2
sig_func:17 -- SIGUSR1 signal 24855,139649254037312

func:44 -- get a semaphore thread_id = 139649219925760
func:45 -- thread pid = 24855
sig_func child thread:2
sig_func:17 -- SIGUSR1 signal 24855,139649254037312
sig_func child thread:2
sig_func:17 -- SIGUSR1 signal 24855,139649254037312
sig_func child thread:2

小结