Linux高性能服务器编程——定时器



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 64class 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 5static 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 5000int 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}