进程池实现

本文是基于半同步/半异步进程池的实现，半同步/半异步模型主要是主进程监视listen套接字，然后发信号给子进程，子进程完成链接和读写数据。

本文实现的进程池特点：

1.使用epoll实现i/0复用；

2.实现信号和i/o事件的统一事件源。

3.使用管道进行子进程和父进程的通信。

代码如下：

#ifndef PROCESSPOOL_H
#define PROCESSPOOL_H

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <assert.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/epoll.h>
#include <signal.h>
#include <sys/wait.h>
#include <sys/stat.h>
/*描述一个子进程的类，m_pid是目标子进程的PID，m_pipefd是父进程和子进程通信用的管道*/
class process
{
public:
    process() : m_pid( -1 ){}

public:
    pid_t m_pid;
    int m_pipefd[2];
};
/*进程池类，将它定义为模板类是为了代码复用。其模板参数是处理逻辑任务的类*/
template< typename T >
class processpool
{
private:
    /*将构造函数定义为私有的，因此我们只能通过后面的create静态函数来创建processpool实例*/
    processpool( int listenfd, int process_number = 8 );
public:
	/*单体模式，以保证程序最多创建一个processpool实例，这是程序正确处理信号的必要条件*/
    static processpool< T >* create( int listenfd, int process_number = 8 )
    {
        if( !m_instance )
        {
            m_instance = new processpool< T >( listenfd, process_number );
        }
        return m_instance;
    }
    ~processpool()
    {
        delete [] m_sub_process;
    }
    /*启动进程池*/
    void run();

private:
    void setup_sig_pipe();
    void run_parent();
    void run_child();

private:
    /*进程池允许的最大子进程数量*/
    static const int MAX_PROCESS_NUMBER = 16;
    /*每个子进程最多能处理的客户数量*/
    static const int USER_PER_PROCESS = 65536;
    /*epoll最多能处理的事件数*/
    static const int MAX_EVENT_NUMBER = 10000;
    /*进程池中的进程总数*/
    int m_process_number;
    /*子进程在池中的序号，从0开始*/
    int m_idx;
    /*每个进程都有一个epoll内核时间，用m_epollfd标识*/
    int m_epollfd;
    /*监听socket*/
    int m_listenfd;
    /*子进程通过m_stop来决定是否停止运行*/
    int m_stop;
    /*保存所有子进程的描述信息*/
    process* m_sub_process;
    /*进程池静态实例*/
    static processpool< T >* m_instance;
};
template< typename T >
processpool< T >* processpool< T >::m_instance = NULL;
/*用于处理信号的管道，以实现同意事件源。后面称之为信号管道*/
static int sig_pipefd[2];

static int setnonblocking( int fd )
{
    int old_option = fcntl( fd, F_GETFL );
    int new_option = old_option | O_NONBLOCK;
    fcntl( fd, F_SETFL, new_option );
    return old_option;
}

static void addfd( int epollfd, int fd )
{
    epoll_event event;
    event.data.fd = fd;
    event.events = EPOLLIN | EPOLLET;
    epoll_ctl( epollfd, EPOLL_CTL_ADD, fd, &event );
    setnonblocking( fd );
}
/*从epollfd标识的epoll内核时间表中删除fd上的所有注册事件*/
static void removefd( int epollfd, int fd )
{
    epoll_ctl( epollfd, EPOLL_CTL_DEL, fd, 0 );
    close( fd );
}
/*信号处理函数*/
static void sig_handler( int sig )
{
    int save_errno = errno;
    int msg = sig;
    send( sig_pipefd[1], ( char* )&msg, 1, 0 );
    errno = save_errno;
}
/*设置信号处理函数*/
static void addsig( int sig, void( handler )(int), bool restart = true )
{
    struct sigaction sa;
    memset( &sa, '\0', sizeof( sa ) );
    sa.sa_handler = handler;
    if( restart )
    {
        sa.sa_flags |= SA_RESTART;
    }
    sigfillset( &sa.sa_mask );
    assert( sigaction( sig, &sa, NULL ) != -1 );
}
/*进程池构造函数。参数listenfd是监听socket，它必须在创建进程池之前被创建，否则子进程无法直接引用它。
参数process_number指定进程池中子进程的数量*/
template< typename T >
processpool< T >::processpool( int listenfd, int process_number ) 
    : m_listenfd( listenfd ), m_process_number( process_number ), m_idx( -1 ), m_stop( false )
{
    assert( ( process_number > 0 ) && ( process_number <= MAX_PROCESS_NUMBER ) );

    m_sub_process = new process[ process_number ];
    assert( m_sub_process );
    /*创建process_number个子进程，并建立它们和父进程之间的管道*/
    for( int i = 0; i < process_number; ++i )
    {
        int ret = socketpair( PF_UNIX, SOCK_STREAM, 0, m_sub_process[i].m_pipefd );
        assert( ret == 0 );

        m_sub_process[i].m_pid = fork();
        assert( m_sub_process[i].m_pid >= 0 );
        if( m_sub_process[i].m_pid > 0 )
        {
            close( m_sub_process[i].m_pipefd[1] );
            continue;
        }
        else
        {
            close( m_sub_process[i].m_pipefd[0] );
            m_idx = i;
            break;
        }
    }
}
/*统一事件源*/
template< typename T >
void processpool< T >::setup_sig_pipe()
{
    /*创建epoll事件监听表和信号管道*/
    m_epollfd = epoll_create( 5 );
    assert( m_epollfd != -1 );

    int ret = socketpair( PF_UNIX, SOCK_STREAM, 0, sig_pipefd );
    assert( ret != -1 );

    setnonblocking( sig_pipefd[1] );
    addfd( m_epollfd, sig_pipefd[0] );
    /*设置信号处理函数*/
    addsig( SIGCHLD, sig_handler );
    addsig( SIGTERM, sig_handler );
    addsig( SIGINT, sig_handler );
    addsig( SIGPIPE, SIG_IGN );
}
/*父进程中m_idx值为-1，子进程m_idx值大于等于0,我们据此判断接下来要运行的是父进程代码还是子进程代码*/
template< typename T >
void processpool< T >::run()
{
    if( m_idx != -1 )
    {
        run_child();
        return;
    }
    run_parent();
}

template< typename T >
void processpool< T >::run_child()
{
    setup_sig_pipe();
    /*每个子进程都通过其在进程池中的序号值m_idx找到与父进程通信的管道*/
    int pipefd = m_sub_process[m_idx].m_pipefd[ 1 ];
    /*子进程需要监听管道文件描述符piped，因为父进程将通过子进程accept新连接*/
    addfd( m_epollfd, pipefd );

    epoll_event events[ MAX_EVENT_NUMBER ];
    T* users = new T [ USER_PER_PROCESS ];
    assert( users );
    int number = 0;
    int ret = -1;

    while( ! m_stop )
    {
        number = epoll_wait( m_epollfd, events, MAX_EVENT_NUMBER, -1 );
        if ( ( number < 0 ) && ( errno != EINTR ) )
        {
            printf( "epoll failure\n" );
            break;
        }

        for ( int i = 0; i < number; i++ )
        {
            int sockfd = events[i].data.fd;
            if( ( sockfd == pipefd ) && ( events[i].events & EPOLLIN ) )
            {
                int client = 0;
				/*从父、子进程之间的管道读取数据，并将结果保存在变量client中。如果读取成功，则表示有新客户连接到来*/
                ret = recv( sockfd, ( char* )&client, sizeof( client ), 0 );
                if( ( ( ret < 0 ) && ( errno != EAGAIN ) ) || ret == 0 ) 
                {
                    continue;
                }
                else
                {
                    struct sockaddr_in client_address;
                    socklen_t client_addrlength = sizeof( client_address );
                    int connfd = accept( m_listenfd, ( struct sockaddr* )&client_address, &client_addrlength );
                    if ( connfd < 0 )
                    {
                        printf( "errno is: %d\n", errno );
                        continue;
                    }
                    addfd( m_epollfd, connfd );
					/*模板类T必须实现init方法，以初始化一个客户连接。我们直接使用connfd来索引逻辑处理对象（T类型的对象），
					以提高程序效率*/
                    users[connfd].init( m_epollfd, connfd, client_address );
                }
            }
			/*下面处理子进程接收到的信号*/
            else if( ( sockfd == sig_pipefd[0] ) && ( events[i].events & EPOLLIN ) )
            {
                int sig;
                char signals[1024];
                ret = recv( sig_pipefd[0], signals, sizeof( signals ), 0 );
                if( ret <= 0 )
                {
                    continue;
                }
                else
                {
                    for( int i = 0; i < ret; ++i )
                    {
                        switch( signals[i] )
                        {
                            case SIGCHLD:
                            {
                                pid_t pid;
                                int stat;
                                while ( ( pid = waitpid( -1, &stat, WNOHANG ) ) > 0 )
                                {
                                    continue;
                                }
                                break;
                            }
                            case SIGTERM:
                            case SIGINT:
                            {
                                m_stop = true;
                                break;
                            }
                            default:
                            {
                                break;
                            }
                        }
                    }
                }
            }
            else if( events[i].events & EPOLLIN )
            {
                 users[sockfd].process();
            }
            else
            {
                continue;
            }
        }
    }

    delete [] users;
    users = NULL;
    close( pipefd );
    //close( m_listenfd ); 
	/*我们将上面这句话注释掉，以提醒读者：应该由m_listenfd的创建者来关闭这个文件描述符，
	及所谓的“对象由哪个函数创建，就应该由哪个函数销毁”*/
    close( m_epollfd );
}

template< typename T >
void processpool< T >::run_parent()
{
    setup_sig_pipe();
	/*父进程监听m_listenfd*/
    addfd( m_epollfd, m_listenfd );

    epoll_event events[ MAX_EVENT_NUMBER ];
    int sub_process_counter = 0;
    int new_conn = 1;
    int number = 0;
    int ret = -1;

    while( ! m_stop )
    {
        number = epoll_wait( m_epollfd, events, MAX_EVENT_NUMBER, -1 );
        if ( ( number < 0 ) && ( errno != EINTR ) )
        {
            printf( "epoll failure\n" );
            break;
        }

        for ( int i = 0; i < number; i++ )
        {
            int sockfd = events[i].data.fd;
            if( sockfd == m_listenfd )
            {
                int i =  sub_process_counter;
                do
                {
                    if( m_sub_process[i].m_pid != -1 )
                    {
                        break;
                    }
                    i = (i+1)%m_process_number;
                }
                while( i != sub_process_counter );
                
                if( m_sub_process[i].m_pid == -1 )
                {
                    m_stop = true;
                    break;
                }
                sub_process_counter = (i+1)%m_process_number;
                //send( m_sub_process[sub_process_counter++].m_pipefd[0], ( char* )&new_conn, sizeof( new_conn ), 0 );
                send( m_sub_process[i].m_pipefd[0], ( char* )&new_conn, sizeof( new_conn ), 0 );
                printf( "send request to child %d\n", i );
                //sub_process_counter %= m_process_number;
            }
			/*下面处理父进程接收到的信号*/
            else if( ( sockfd == sig_pipefd[0] ) && ( events[i].events & EPOLLIN ) )
            {
                int sig;
                char signals[1024];
                ret = recv( sig_pipefd[0], signals, sizeof( signals ), 0 );
                if( ret <= 0 )
                {
                    continue;
                }
                else
                {
                    for( int i = 0; i < ret; ++i )
                    {
                        switch( signals[i] )
                        {
                            case SIGCHLD:
                            {
                                pid_t pid;
                                int stat;
                                while ( ( pid = waitpid( -1, &stat, WNOHANG ) ) > 0 )
                                {
                                    for( int i = 0; i < m_process_number; ++i )
                                    {
									/*如果进程池中第i个子进程退出了，则主进程关闭相应的通信管道，并设置相应的m_pid为-1，
									以标记该子进程已经退出*/
                                        if( m_sub_process[i].m_pid == pid )
                                        {
                                            printf( "child %d join\n", i );
                                            close( m_sub_process[i].m_pipefd[0] );
                                            m_sub_process[i].m_pid = -1;
                                        }
                                    }
                                }
                                m_stop = true;
                                for( int i = 0; i < m_process_number; ++i )
                                {
                                    if( m_sub_process[i].m_pid != -1 )
                                    {
                                        m_stop = false;
                                    }
                                }
                                break;
                            }
                            case SIGTERM:
                            case SIGINT:
                            {
								/*如果父进程接收到终止信号，那么就杀死所有子进程，并等待它们全部结束。当然，通知子进程结束
								更好的方法是向父、子进程之间的通信管道发送页数数据*/
                                printf( "kill all the clild now\n" );
                                for( int i = 0; i < m_process_number; ++i )
                                {
                                    int pid = m_sub_process[i].m_pid;
                                    if( pid != -1 )
                                    {
                                        kill( pid, SIGTERM );
                                    }
                                }
                                break;
                            }
                            default:
                            {
                                break;
                            }
                        }
                    }
                }
            }
            else
            {
                continue;
            }
        }
    }

    //close( m_listenfd );
	/*由创建者关闭上面这个文件描述符*/
    close( m_epollfd );
}

#endif