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本章内容解读SRS开源代码框架，无二次开发，以学习交流为目的。

SRS是国人开发的开源流媒体服务器，C++语言开发，本章使用版本：

https://github.com/ossrs/srs/tree/5.0release

。

SRS信号量的使用

SRS封装了SrsSignalManager类，注册信号量回调函数，使用linux无名管道，接收到信号量时写入管道，在协程里轮询读取管道里的信号，并作相关处理。

信号量的使用提供了用户进程（命令行即可）与正在运行的SRS程序通信的方式，SRS使用信号量实现的功能：强制退出程序、优雅地退出程序（执行一系列析构，停止监听等）、重新加载配置文件、日志文件切割等。

源码

SRS使用的是协程轮询，这里使用传统线程轮询，用法类似。

srs_app_server.hpp

#ifndef SRS_APP_SERVER_HPP
#define SRS_APP_SERVER_HPP

#include <vector>
#include <string>
typedef int srs_error_t;
#define srs_success 0

// 系统信号量宏定义
// The signal defines.
// To reload the config file and apply new config.
#define SRS_SIGNAL_RELOAD SIGHUP
// Reopen the log file.
#define SRS_SIGNAL_REOPEN_LOG SIGUSR1
// For gracefully upgrade, start new SRS and gracefully quit old one.
// @see https://github.com/ossrs/srs/issues/1579
// TODO: Not implemented.
#define SRS_SIGNAL_UPGRADE SIGUSR2
// The signal for srs to fast quit, do essential dispose then exit.
#define SRS_SIGNAL_FAST_QUIT SIGTERM
// The signal for srs to gracefully quit, do carefully dispose then exit.
// @see https://github.com/ossrs/srs/issues/1579
#define SRS_SIGNAL_GRACEFULLY_QUIT SIGQUIT
// The signal for SRS to abort by assert(false).
#define SRS_SIGNAL_ASSERT_ABORT SIGABRT

// The application level signals.
// Persistence the config in memory to config file.
// @see https://github.com/ossrs/srs/issues/319#issuecomment-134993922
// @remark we actually don't handle the signal for it's not a valid os signal.
#define SRS_SIGNAL_PERSISTENCE_CONFIG 1000


// Convert signal to io,
// @see: st-1.9/docs/notes.html
class SrsSignalManager /*: public ISrsCoroutineHandler*/
{
private:
    // Per-process pipe which is used as a signal queue.
    // Up to PIPE_BUF/sizeof(int) signals can be queued up.
    int sig_pipe[2];//无名管道，fd[0]负责读，fd[1]负责写
    /*srs_netfd_t*/int signal_read_stfd;
private:
//    SrsServer* server;
//    SrsCoroutine* trd;
public:
    SrsSignalManager(/*SrsServer* s*/);
    virtual ~SrsSignalManager();
public:
    virtual srs_error_t initialize();
    virtual srs_error_t start();//监听信号，开启线程轮询
// Interface ISrsEndlessThreadHandler.
public:
    static void* startThread(void* obj);//SRS是在协程轮询读信号，这里改为传统线程轮询，用法类似
    virtual void *cycle();//轮询读取管道
    void on_signal(int signo);
private:
    // Global singleton instance
    static SrsSignalManager* instance;
    // Signal catching function.
    // Converts signal event to I/O event.
    static void sig_catcher(int signo);//信号捕获回调函数
};


#endif

srs_app_server.cpp

#include <srs_app_server.hpp>

#include <sys/types.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <algorithm>
#include <assert.h>
#if !defined(SRS_OSX) && !defined(SRS_CYGWIN64)
#include <sys/inotify.h>
#endif
using namespace std;


#ifdef SRS_RTC
#include <srs_app_rtc_network.hpp>
#endif
#ifdef SRS_GB28181
#include <srs_app_gb28181.hpp>
#endif

SrsSignalManager* SrsSignalManager::instance = NULL;

SrsSignalManager::SrsSignalManager()
{
    SrsSignalManager::instance = this;
    
//    server = s;
    sig_pipe[0] = sig_pipe[1] = -1;
//    trd = new SrsSTCoroutine("signal", this, _srs_context->get_id());
//    signal_read_stfd = NULL;
}

SrsSignalManager::~SrsSignalManager()
{
//    srs_freep(trd);

//    srs_close_stfd(signal_read_stfd);
    
    if (sig_pipe[0] > 0) {
        ::close(sig_pipe[0]);
    }
    if (sig_pipe[1] > 0) {
        ::close(sig_pipe[1]);
    }
}

srs_error_t SrsSignalManager::initialize()
{
    /* Create signal pipe */
    //创建管道
    if (pipe(sig_pipe) < 0) {
        printf( "create pipe,ERROR_SYSTEM_CREATE_PIPE\n");
        return -1;
    }

//    if ((signal_read_stfd = srs_netfd_open(sig_pipe[0])) == NULL) {
//        return srs_error_new(ERROR_SYSTEM_CREATE_PIPE, "open pipe");
//    }
    
    return srs_success;
}

srs_error_t SrsSignalManager::start()
{
    srs_error_t err = srs_success;
    
    /**
     * Note that if multiple processes are used (see below),
     * the signal pipe should be initialized after the fork(2) call
     * so that each process has its own private pipe.
     */
    struct sigaction sa;
    
    //sigemptyset：将信号集置空
    //sigaction：为信号指定相关的处理程序
    /* Install sig_catcher() as a signal handler */
    sa.sa_handler = SrsSignalManager::sig_catcher;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
    sigaction(SRS_SIGNAL_RELOAD, &sa, NULL);
    
    sa.sa_handler = SrsSignalManager::sig_catcher;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
    sigaction(SRS_SIGNAL_FAST_QUIT, &sa, NULL);

    sa.sa_handler = SrsSignalManager::sig_catcher;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
    sigaction(SRS_SIGNAL_GRACEFULLY_QUIT, &sa, NULL);

    sa.sa_handler = SrsSignalManager::sig_catcher;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
    sigaction(SRS_SIGNAL_ASSERT_ABORT, &sa, NULL);
    
    sa.sa_handler = SrsSignalManager::sig_catcher;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
    sigaction(SIGINT, &sa, NULL);
    
    sa.sa_handler = SrsSignalManager::sig_catcher;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
    sigaction(SRS_SIGNAL_REOPEN_LOG, &sa, NULL);
    
    printf("signal installed, reload=%d, reopen=%d, fast_quit=%d, grace_quit=%d\n",
              SRS_SIGNAL_RELOAD, SRS_SIGNAL_REOPEN_LOG, SRS_SIGNAL_FAST_QUIT, SRS_SIGNAL_GRACEFULLY_QUIT);
    
//    if ((err = trd->start()) != srs_success) {//执行协程处理函数
//        return srs_error_wrap(err, "signal manager");
//    }
    pthread_t tid;
    pthread_create(&tid,NULL,SrsSignalManager::startThread,this);
    
    return err;
}

void *SrsSignalManager::startThread(void *obj)
{
    SrsSignalManager* pSrsSignalManager = (SrsSignalManager*)obj;
    pSrsSignalManager->cycle();

    return nullptr;
}

void* SrsSignalManager::cycle()
{  
    while (true) {
        int signo;
        
        /* Read the next signal from the pipe */
        //从管道读取数据
        /*srs_read*/read(sig_pipe[0], &signo, sizeof(int)/*, SRS_UTIME_NO_TIMEOUT*/);
        
        /* Process signal synchronously */
        on_signal(signo);
        usleep(1000);
    }
    
    return nullptr;
}

void SrsSignalManager::sig_catcher(int signo)
{
    int err;
    
    /* Save errno to restore it after the write() */
    err = errno;
    
    /* write() is reentrant/async-safe */
    int fd = SrsSignalManager::instance->sig_pipe[1];//往管道里写数据
    write(fd, &signo, sizeof(int));
    
    errno = err;
}


void SrsSignalManager::on_signal(int signo)
{
    // For signal to quit with coredump.
    if (signo == SRS_SIGNAL_ASSERT_ABORT) {
        printf("abort with coredump, signo=%d\n", signo);
        assert(false);
        return;
    }

    if (signo == SRS_SIGNAL_RELOAD) {
        printf("reload config, signo=%d\n", signo);
        return;
    }

#ifndef SRS_GPERF_MC
    if (signo == SRS_SIGNAL_REOPEN_LOG) {
        printf("reopen log file, signo=%d\n", signo);
        return;
    }
#endif

#ifdef SRS_GPERF_MC
    if (signo == SRS_SIGNAL_REOPEN_LOG) {
        signal_gmc_stop = true;
        srs_warn("for gmc, the SIGUSR1 used as SIGINT, signo=%d", signo);
        return;
    }
#endif

    if (signo == SRS_SIGNAL_PERSISTENCE_CONFIG) {
        return;
    }

    if (signo == SIGINT) {
#ifdef SRS_GPERF_MC
        srs_trace("gmc is on, main cycle will terminate normally, signo=%d", signo);
        signal_gmc_stop = true;
#endif
    }

    // For K8S, force to gracefully quit for gray release or canary.
    // @see https://github.com/ossrs/srs/issues/1595#issuecomment-587473037
    if (signo == SRS_SIGNAL_FAST_QUIT ) {
        printf("force gracefully quit, signo=%d\n", signo);
        signo = SRS_SIGNAL_GRACEFULLY_QUIT;
    }

    if ((signo == SIGINT || signo == SRS_SIGNAL_FAST_QUIT) ) {
        printf("sig=%d, user terminate program, fast quit\n", signo);
        return;
    }

    if (signo == SRS_SIGNAL_GRACEFULLY_QUIT ) {
        printf("sig=%d, user start gracefully quit\n年", signo);
        return;
    }
}

源码测试

程序运行后，在命令行执行：

killall -s SIGUSR1 srs_Signal		#srs_Signal是进程名

srs_Signal进程打印

signal installed, reload=1, reopen=10, fast_quit=15, grace_quit=3
reopen log file, signo=10			#发送SIGUSR1 信号时打印
force gracefully quit, signo=15		#Ctrl+c 强制退出时打印
sig=3, user start gracefully quit	#Ctrl+c 强制退出时打印