processpool.h

#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;
    //number of total processes
    int m_process_number;
    //index of subprocess, begin with 0
    int m_idx;
    //epoll events table in each process, using m_epollfd to identify
    int m_epollfd;
    //listening socket fd
    int m_listenfd;
    // flag of whether subprocess should stop or not
    int m_stop;
    //varaible of record all subprocess desc 
    process *m_sub_process;
    //static instance of process pool
    static processpool<T> *m_instance;
};

//pipe used to handle signal 
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);
}

static void removefd(int epollfd, int fd)
{
    epoll_ctl(epollfd, EPOLL_CTL_DEL, fd, 0);
    close(fd);
}

static void sig_handler(int sig)
{
    int save_errno = errno;
    int msg = sig;
    send(sig_pipefd[1], (char *)msg, 1, 0);
    errno = save_errno;
}

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_nubmer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, 子进程中m_idx值大于等于0,
//我们据此判断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pipefd，
    //因为父进程将通过它来通知子进程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_PROCESS_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_addresslength = sizeof(client_address);
                    int connfd = accept(m_listenfd, (struct sockaddr*)&client_address, &client_addresslength);
                    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;
                                }
                        }
                    }
                }
            }
            //如果是其他可读数据，
            //那么必然是客户请求到来。调用逻辑处理对象的process方法处理之一
            else if (events[i].events & EPOLLIN) 
            {
                users[sockfd].process();
            }
            else
            {
                continue;
            }
        }
    }

    delete [] users;
    users = NULL;
    close(pipefd);
    //close(m_listenfd);
    ////我们将这句话注释掉，以提醒读者：应该m_listenfd的创建者来关闭这个文件描述符（见
    //后文），即所谓的“对象（比如一个文件描述符，又或者一段堆内存）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) 
            {
                //如果有新连接到来，就采用Round
                //Robin方式将其分配给一个子进程处理
                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[i].m_pipefd[0],
                        (char *)&new_conn, sizeof(new_conn), 0);
                printf("send request to child %d\n", i);

            }
            //下面处理父进程接收的信号
            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(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;
                                            }
                                        }
                                    }
                                    //如果所有子进程都已经退出了，则父进程也退出
                                    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特殊数据，
                                    //读者不妨自己实现之
                                    printf("kill all the child 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); //由创建者关闭这个文件描述符（见后文）
    close(m_epollfd);
}

#endif