定时器

服务器程序通常管理着众多定时事件，因此有效组织这些定时事件，使之能在预期的时间点被触发且不影响服务器的主要逻辑，对于服务器的性能有着至关重要的影响。位置我们要将每个定时事件封装成定时器，并使用某种容器类型的数据结构，比如链表、排序链表和时间轮将所有定时器串联起来，以实现对定时事件的统一管理。

Linux提供三种定时方法：

1.socket选项SO_RECVTIMEO和SO_SNDTIMEO。

2.SIGALRM信号

3.I/O复用系统调用的超时参数

socket选项SO_RCVTIMEO和SO_SNDTIMEO

SO_RCVTIMEO和SO_SNDTIMEO选项分别用来设置socket接收数据超时时间和发送数据超时时间。因此这两个选项仅对数据接收和发送相关的socket专用系统调用有效，这些系统调用包括send、sendmsg、recv、recvmsg、accept和connect。

程序清单1展示了使用SO_SNDTIMEP选项来定时：

SIGALRM信号

由alarm和setitimer函数设置的实时闹钟一旦超时，将触发SIGALRM信号。因此，我们可以利用该信号的信号处理函数来处理定时任务。但是，如果要处理多个定时任务，我们就需要不断触发SIGALRM信号，并在其信号处理函数中执行到期的任务。一般而言，SIGALRM信号按照固定频率生成，即由alarm或setitimer函数设计的定时周期T保持不变。如果某个定时任务的超时时间不是T的整数倍，那么它实际被执行的时间和预期的时间将略有偏差。因此定时周期T反映了定时的精度。

程序清单2定义了一个定时器链表，程序清单3展示如何使用SIGALRM信号处理非活动连接。

I/O复用系统调用

Linux下的3组I/O复用系统调用都带有超时参数，因此他们不仅能同意处理信号和I/O事件，也能统一处理定时事件。但是由于I/O复用系统可能在超时时间到期之前就返回，所以如果我们能要利用它们来定时，就需要不断更新定时参数以反映剩余的时间:

程序清单4展示了利用I/O复用系统调用定时：

高性能定时器

时间轮

基于排序链表的定时器存在一个问题：添加定时器的效率偏低。下面我们要讨论的时间轮解决了这个问题，一种简单的时间轮如图所示：

上图所示的时间轮，实现指针指向轮子的一个槽。它以恒定的速度顺时转动，每转动一步就指向下一个槽，每次转动称为一个滴答。一个滴答的时间称为时间轮的槽间隔si，它时间上就是心搏时间。该时间轮共有N个槽，因此转一圈时间是N*si。每个槽指向一跳定时器链表，每条链表上的定时器具有相同的特征：他们的定时时间差JN*si的整数倍。很显然，对时间轮而言，要提高定时精度，就要使si值足够小；要提高执行效率，则要求N值足够大。

时间堆

前面讨论的定时方案都是以固定是频率调用心搏函数tick，并在其中一次检测到期的定时器，然后执行到期定时器上的回调函数。设计定时器的另一种思路是：将所有定时器中超时时间最小的一个定时器的超时值作为心搏间隔。这样，一旦心搏函数tick被调用，超时时间最小的定时器必然到期，我们就可以在tick函数中处理该定时器。然后，再次从剩余的定时器中找出超时时间最小的一个，并将这段最小时间设置为下一次心搏间隔。时间堆就是利用最小堆来是实现上述方案。

程序清单1：
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <assert.h>
#include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>

int timeout_connect( const char* ip, int port, int time )
{
    int ret = 0;
    struct sockaddr_in address;
    bzero( &address, sizeof( address ) );
    address.sin_family = AF_INET;
    inet_pton( AF_INET, ip, &address.sin_addr );
    address.sin_port = htons( port );

    int sockfd = socket( PF_INET, SOCK_STREAM, 0 );
    assert( sockfd >= 0 );

    struct timeval timeout;
    timeout.tv_sec = time;
    timeout.tv_usec = 0;
    socklen_t len = sizeof( timeout );
    ret = setsockopt( sockfd, SOL_SOCKET, SO_SNDTIMEO, &timeout, len );
    assert( ret != -1 );

    ret = connect( sockfd, ( struct sockaddr* )&address, sizeof( address ) );
    if ( ret == -1 )
    {
        if( errno == EINPROGRESS )
        {
            printf( "connecting timeout\n" );
            return -1;
        }
        printf( "error occur when connecting to server\n" );
        return -1;
    }

    return sockfd;
}

int main( int argc, char* argv[] )
{
    if( argc <= 2 )
    {
        printf( "usage: %s ip_address port_number\n", basename( argv[0] ) );
        return 1;
    }
    const char* ip = argv[1];
    int port = atoi( argv[2] );

    int sockfd = timeout_connect( ip, port, 10 );
    if ( sockfd < 0 )
    {
        return 1;
    }
    return 0;
}

程序清单2：
#ifndef LST_TIMER
#define LST_TIMER

#include <time.h>

#define BUFFER_SIZE 64
class util_timer;
struct client_data
{
    sockaddr_in address;
    int sockfd;
    char buf[ BUFFER_SIZE ];
    util_timer* timer;
};

class util_timer
{
public:
    util_timer() : prev( NULL ), next( NULL ){}

public:
   time_t expire; 
   void (*cb_func)( client_data* );
   client_data* user_data;
   util_timer* prev;
   util_timer* next;
};

class sort_timer_lst
{
public:
    sort_timer_lst() : head( NULL ), tail( NULL ) {}
    ~sort_timer_lst()
    {
        util_timer* tmp = head;
        while( tmp )
        {
            head = tmp->next;
            delete tmp;
            tmp = head;
        }
    }
    void add_timer( util_timer* timer )
    {
        if( !timer )
        {
            return;
        }
        if( !head )
        {
            head = tail = timer;
            return; 
        }
        if( timer->expire < head->expire )
        {
            timer->next = head;
            head->prev = timer;
            head = timer;
            return;
        }
        add_timer( timer, head );
    }
    void adjust_timer( util_timer* timer )
    {
        if( !timer )
        {
            return;
        }
        util_timer* tmp = timer->next;
        if( !tmp || ( timer->expire < tmp->expire ) )
        {
            return;
        }
        if( timer == head )
        {
            head = head->next;
            head->prev = NULL;
            timer->next = NULL;
            add_timer( timer, head );
        }
        else
        {
            timer->prev->next = timer->next;
            timer->next->prev = timer->prev;
            add_timer( timer, timer->next );
        }
    }
    void del_timer( util_timer* timer )
    {
        if( !timer )
        {
            return;
        }
        if( ( timer == head ) && ( timer == tail ) )
        {
            delete timer;
            head = NULL;
            tail = NULL;
            return;
        }
        if( timer == head )
        {
            head = head->next;
            head->prev = NULL;
            delete timer;
            return;
        }
        if( timer == tail )
        {
            tail = tail->prev;
            tail->next = NULL;
            delete timer;
            return;
        }
        timer->prev->next = timer->next;
        timer->next->prev = timer->prev;
        delete timer;
    }
    void tick()
    {
        if( !head )
        {
            return;
        }
        printf( "timer tick\n" );
        time_t cur = time( NULL );
        util_timer* tmp = head;
        while( tmp )
        {
            if( cur < tmp->expire )
            {
                break;
            }
            tmp->cb_func( tmp->user_data );
            head = tmp->next;
            if( head )
            {
                head->prev = NULL;
            }
            delete tmp;
            tmp = head;
        }
    }

private:
    void add_timer( util_timer* timer, util_timer* lst_head )
    {
        util_timer* prev = lst_head;
        util_timer* tmp = prev->next;
        while( tmp )
        {
            if( timer->expire < tmp->expire )
            {
                prev->next = timer;
                timer->next = tmp;
                tmp->prev = timer;
                timer->prev = prev;
                break;
            }
            prev = tmp;
            tmp = tmp->next;
        }
        if( !tmp )
        {
            prev->next = timer;
            timer->prev = prev;
            timer->next = NULL;
            tail = timer;
        }
        
    }

private:
    util_timer* head;
    util_timer* tail;
};

#endif

程序清单3
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <assert.h>
#include <stdio.h>
#include <signal.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/epoll.h>
#include <pthread.h>
#include "lst_timer.h"

#define FD_LIMIT 65535
#define MAX_EVENT_NUMBER 1024
#define TIMESLOT 5

static int pipefd[2];
static sort_timer_lst timer_lst;
static int epollfd = 0;

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;
}

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 );
}

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

void addsig( int sig )
{
    struct sigaction sa;
    memset( &sa, '\0', sizeof( sa ) );
    sa.sa_handler = sig_handler;
    sa.sa_flags |= SA_RESTART;
    sigfillset( &sa.sa_mask );
    assert( sigaction( sig, &sa, NULL ) != -1 );
}

void timer_handler()
{
    timer_lst.tick();
    alarm( TIMESLOT );
}

void cb_func( client_data* user_data )
{
    epoll_ctl( epollfd, EPOLL_CTL_DEL, user_data->sockfd, 0 );
    assert( user_data );
    close( user_data->sockfd );
    printf( "close fd %d\n", user_data->sockfd );
}

int main( int argc, char* argv[] )
{
    if( argc <= 2 )
    {
        printf( "usage: %s ip_address port_number\n", basename( argv[0] ) );
        return 1;
    }
    const char* ip = argv[1];
    int port = atoi( argv[2] );

    int ret = 0;
    struct sockaddr_in address;
    bzero( &address, sizeof( address ) );
    address.sin_family = AF_INET;
    inet_pton( AF_INET, ip, &address.sin_addr );
    address.sin_port = htons( port );

    int listenfd = socket( PF_INET, SOCK_STREAM, 0 );
    assert( listenfd >= 0 );

    ret = bind( listenfd, ( struct sockaddr* )&address, sizeof( address ) );
    assert( ret != -1 );

    ret = listen( listenfd, 5 );
    assert( ret != -1 );

    epoll_event events[ MAX_EVENT_NUMBER ];
    int epollfd = epoll_create( 5 );
    assert( epollfd != -1 );
    addfd( epollfd, listenfd );

    ret = socketpair( PF_UNIX, SOCK_STREAM, 0, pipefd );
    assert( ret != -1 );
    setnonblocking( pipefd[1] );
    addfd( epollfd, pipefd[0] );

    // add all the interesting signals here
    addsig( SIGALRM );
    addsig( SIGTERM );
    bool stop_server = false;

    client_data* users = new client_data[FD_LIMIT]; 
    bool timeout = false;
    alarm( TIMESLOT );

    while( !stop_server )
    {
        int number = epoll_wait( 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 == listenfd )
            {
                struct sockaddr_in client_address;
                socklen_t client_addrlength = sizeof( client_address );
                int connfd = accept( listenfd, ( struct sockaddr* )&client_address, &client_addrlength );
                addfd( epollfd, connfd );
                users[connfd].address = client_address;
                users[connfd].sockfd = connfd;
                util_timer* timer = new util_timer;
                timer->user_data = &users[connfd];
                timer->cb_func = cb_func;
                time_t cur = time( NULL );
                timer->expire = cur + 3 * TIMESLOT;
                users[connfd].timer = timer;
                timer_lst.add_timer( timer );
            }
            else if( ( sockfd == pipefd[0] ) && ( events[i].events & EPOLLIN ) )
            {
                int sig;
                char signals[1024];
                ret = recv( pipefd[0], signals, sizeof( signals ), 0 );
                if( ret == -1 )
                {
                    // handle the error
                    continue;
                }
                else if( ret == 0 )
                {
                    continue;
                }
                else
                {
                    for( int i = 0; i < ret; ++i )
                    {
                        switch( signals[i] )
                        {
                            case SIGALRM:
                            {
                                timeout = true;
                                break;
                            }
                            case SIGTERM:
                            {
                                stop_server = true;
                            }
                        }
                    }
                }
            }
            else if(  events[i].events & EPOLLIN )
            {
                memset( users[sockfd].buf, '\0', BUFFER_SIZE );
                ret = recv( sockfd, users[sockfd].buf, BUFFER_SIZE-1, 0 );
                printf( "get %d bytes of client data %s from %d\n", ret, users[sockfd].buf, sockfd );
                util_timer* timer = users[sockfd].timer;
                if( ret < 0 )
                {
                    if( errno != EAGAIN )
                    {
                        cb_func( &users[sockfd] );
                        if( timer )
                        {
                            timer_lst.del_timer( timer );
                        }
                    }
                }
                else if( ret == 0 )
                {
                    cb_func( &users[sockfd] );
                    if( timer )
                    {
                        timer_lst.del_timer( timer );
                    }
                }
                else
                {
                    //send( sockfd, users[sockfd].buf, BUFFER_SIZE-1, 0 );
                    if( timer )
                    {
                        time_t cur = time( NULL );
                        timer->expire = cur + 3 * TIMESLOT;
                        printf( "adjust timer once\n" );
                        timer_lst.adjust_timer( timer );
                    }
                }
            }
            else
            {
                // others
            }
        }

        if( timeout )
        {
            timer_handler();
            timeout = false;
        }
    }

    close( listenfd );
    close( pipefd[1] );
    close( pipefd[0] );
    delete [] users;
    return 0;
}

程序清单4
#define TIMEOUT 5000

int timeout = TIMEOUT;
time_t start = time( NULL );
time_t end = time( NULL );
while( 1 )
{
    printf( "the timeout is now %d mill-seconds\n", timeout );
    start = time( NULL );
    int number = epoll_wait( epollfd, events, MAX_EVENT_NUMBER, timeout );
    if( ( number < 0 ) && ( errno != EINTR ) )
    {
        printf( "epoll failure\n" );
        break;
    }
    if( number == 0 )
    {
        // timeout
        timeout = TIMEOUT;
        continue;
    }

    end = time( NULL );
    timeout -= ( end - start ) * 1000;
    if( timeout <= 0 )
    {
        // timeout
        timeout = TIMEOUT;
    }

    // handle connections
}

Linux高性能服务器编程——定时器,古老的榕树,5-wow.com