三種新的fd加入linux內(nèi)核的的版本：
signalfd：2.6.22
timerfd：2.6.25
eventfd：2.6.22
三種fd的意義：
lsignalfd
傳統(tǒng)的處理信號(hào)的方式是注冊(cè)信號(hào)處理函數(shù)；由于信號(hào)是異步發(fā)生的，要解決數(shù)據(jù)的并發(fā)訪問(wèn)，可重入問(wèn)題。signalfd可以將信號(hào)抽象為一個(gè)文件描述符，當(dāng)有信號(hào)發(fā)生時(shí)可以對(duì)其read，這樣可以將信號(hào)的監(jiān)聽(tīng)放到select、poll、epoll等監(jiān)聽(tīng)隊(duì)列中。
ltimerfd
可以實(shí)現(xiàn)定時(shí)器的功能，將定時(shí)器抽象為文件描述符，當(dāng)定時(shí)器到期時(shí)可以對(duì)其read，這樣也可以放到監(jiān)聽(tīng)隊(duì)列的主循環(huán)中。
leventfd
實(shí)現(xiàn)了線程之間事件通知的方式，也可以用于用戶態(tài)和內(nèi)核通信。eventfd的緩沖區(qū)大小是sizeof(uint64_t)；向其write可以遞增這個(gè)計(jì)數(shù)器，read操作可以讀取，并進(jìn)行清零；eventfd也可以放到監(jiān)聽(tīng)隊(duì)列中，當(dāng)計(jì)數(shù)器不是0時(shí)，有可讀事件發(fā)生，可以進(jìn)行讀取。
三種新的fd都可以進(jìn)行監(jiān)聽(tīng)，當(dāng)有事件觸發(fā)時(shí)，有可讀事件發(fā)生。
signalfd涉及API：
點(diǎn)擊(此處)折疊或打開(kāi)
#include <sys/signalfd.h> int signalfd(int fd, const sigset_t *mask, int flags);#include <sys/signalfd.h> int signalfd(int fd, const sigset_t *mask, int flags);
參數(shù)fd：如果是-1則表示新建一個(gè)，如果是一個(gè)已經(jīng)存在的則表示修改signalfd所關(guān)聯(lián)的信號(hào)；
參數(shù)mask：信號(hào)集合；
參數(shù)flag：內(nèi)核版本2.6.27以后支持SFD_NONBLOCK、SFD_CLOEXEC；
成功返回文件描述符，返回的fd支持以下操作：read、select(poll、epoll)、close
l例子
#include <sys/signalfd.h> #include <signal.h> #include <unistd.h> #include <stdlib.h> #include <stdio.h> #define handle_error(msg) / do { perror(msg); exit(EXIT_FAILURE); } while (0) int main(int argc, char *argv[]) { sigset_t mask; int sfd; struct signalfd_siginfo fdsi; ssize_t s; sigemptyset(&mask); sigaddset(&mask, SIGINT); sigaddset(&mask, SIGQUIT); if (sigprocmask(SIG_BLOCK, &mask, NULL) == -1) handle_error("sigprocmask"); sfd = signalfd(-1, &mask, 0); if (sfd == -1) handle_error("signalfd"); for (;;) { s = read(sfd, &fdsi, sizeof(struct signalfd_siginfo)); if (s != sizeof(struct signalfd_siginfo)) handle_error("read"); if (fdsi.ssi_signo == SIGINT) { printf("Got SIGINT/n"); } else if (fdsi.ssi_signo == SIGQUIT) { printf("Got SIGQUIT/n"); exit(EXIT_SUCCESS); } else { printf("Read unexpected signal/n"); } } }#include <sys/signalfd.h> #include <signal.h> #include <unistd.h> #include <stdlib.h> #include <stdio.h> #define handle_error(msg) / do { perror(msg); exit(EXIT_FAILURE); } while (0) int main(int argc, char *argv[]) { sigset_t mask; int sfd; struct signalfd_siginfo fdsi; ssize_t s; sigemptyset(&mask); sigaddset(&mask, SIGINT); sigaddset(&mask, SIGQUIT); if (sigprocmask(SIG_BLOCK, &mask, NULL) == -1) handle_error("sigprocmask"); sfd = signalfd(-1, &mask, 0); if (sfd == -1) handle_error("signalfd"); for (;;) { s = read(sfd, &fdsi, sizeof(struct signalfd_siginfo)); if (s != sizeof(struct signalfd_siginfo)) handle_error("read"); if (fdsi.ssi_signo == SIGINT) { printf("Got SIGINT/n"); } else if (fdsi.ssi_signo == SIGQUIT) { printf("Got SIGQUIT/n"); exit(EXIT_SUCCESS); } else { printf("Read unexpected signal/n"); } } }L17-L21：將感興趣的信號(hào)加入到sigset_t中；
L24：調(diào)用signalfd，把信號(hào)集與fd關(guān)聯(lián)起來(lái)，第一個(gè)參數(shù)為-1表示新建一個(gè)signalfd，不是-1并且是一個(gè)合法的signalfd表示向其添加新的信號(hào)。
L29：阻塞等待信號(hào)的發(fā)生并讀取。根據(jù)讀取的結(jié)果可以知道發(fā)生了什么信號(hào)。
timerfd涉及的API
#include <sys/timerfd.h> int timerfd_create(int clockid, int flags); int timerfd_settime(int fd, int flags, const struct itimerspec *new_value,struct itimerspec *old_value); int timerfd_gettime(int fd, struct itimerspec *curr_value);#include <sys/timerfd.h> int timerfd_create(int clockid, int flags); int timerfd_settime(int fd, int flags, const struct itimerspec *new_value,struct itimerspec *old_value); int timerfd_gettime(int fd, struct itimerspec *curr_value);timerfd_create：創(chuàng)建一個(gè)timerfd；返回的fd可以進(jìn)行如下操作：read、select(poll、epoll)、closetimerfd_settime：設(shè)置timer的周期，以及起始間隔timerfd_gettime：獲取到期時(shí)間。//函數(shù)參數(shù)中數(shù)據(jù)結(jié)構(gòu)如下： struct timespec { time_t tv_sec; /* Seconds */ long tv_nsec; /* Nanoseconds */ }; struct itimerspec { struct timespec it_interval; /* Interval for periodic timer */ struct timespec it_value; /* Initial expiration */ };//函數(shù)參數(shù)中數(shù)據(jù)結(jié)構(gòu)如下： struct timespec { time_t tv_sec; /* Seconds */ long tv_nsec; /* Nanoseconds */ }; struct itimerspec { struct timespec it_interval; /* Interval for periodic timer */ struct timespec it_value; /* Initial expiration */ };l例子
#include <sys/timerfd.h> #include <sys/time.h> #include <time.h> #include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <stdint.h> /* Definition of uint64_t */ #define handle_error(msg) / do { perror(msg); exit(EXIT_FAILURE); } while (0) void printTime() { struct timeval tv; gettimeofday(&tv, NULL); printf("printTime: current time:%ld.%ld ", tv.tv_sec, tv.tv_usec); } int main(int argc, char *argv[]) { struct timespec now; if (clock_gettime(CLOCK_REALTIME, &now) == -1) handle_error("clock_gettime"); struct itimerspec new_value; new_value.it_value.tv_sec = now.tv_sec + atoi(argv[1]); new_value.it_value.tv_nsec = now.tv_nsec; new_value.it_interval.tv_sec = atoi(argv[2]); new_value.it_interval.tv_nsec = 0; int fd = timerfd_create(CLOCK_REALTIME, 0); if (fd == -1) handle_error("timerfd_create"); if (timerfd_settime(fd, TFD_TIMER_ABSTIME, &new_value, NULL) == -1) handle_error("timerfd_settime"); printTime(); printf("timer started/n"); for (uint64_t tot_exp = 0; tot_exp < atoi(argv[3]);) { uint64_t exp; ssize_t s = read(fd, &exp, sizeof(uint64_t)); if (s != sizeof(uint64_t)) handle_error("read"); tot_exp += exp; printTime(); printf("read: %llu; total=%llu/n",exp, tot_exp); } exit(EXIT_SUCCESS); }#include <sys/timerfd.h> #include <sys/time.h> #include <time.h> #include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <stdint.h> /* Definition of uint64_t */ #define handle_error(msg) / do { perror(msg); exit(EXIT_FAILURE); } while (0) void printTime() { struct timeval tv; gettimeofday(&tv, NULL); printf("printTime: current time:%ld.%ld ", tv.tv_sec, tv.tv_usec); } int main(int argc, char *argv[]) { struct timespec now; if (clock_gettime(CLOCK_REALTIME, &now) == -1) handle_error("clock_gettime"); struct itimerspec new_value; new_value.it_value.tv_sec = now.tv_sec + atoi(argv[1]); new_value.it_value.tv_nsec = now.tv_nsec; new_value.it_interval.tv_sec = atoi(argv[2]); new_value.it_interval.tv_nsec = 0; int fd = timerfd_create(CLOCK_REALTIME, 0); if (fd == -1) handle_error("timerfd_create"); if (timerfd_settime(fd, TFD_TIMER_ABSTIME, &new_value, NULL) == -1) handle_error("timerfd_settime"); printTime(); printf("timer started/n"); for (uint64_t tot_exp = 0; tot_exp < atoi(argv[3]);) { uint64_t exp; ssize_t s = read(fd, &exp, sizeof(uint64_t)); if (s != sizeof(uint64_t)) handle_error("read"); tot_exp += exp; printTime(); printf("read: %llu; total=%llu/n",exp, tot_exp); } exit(EXIT_SUCCESS); }代碼L25-L29：初始化定時(shí)器的參數(shù)，初始間隔與定時(shí)間隔。
L32：創(chuàng)建定時(shí)器fd，CLOCK_REALTIME：真實(shí)時(shí)間類型，修改時(shí)鐘會(huì)影響定時(shí)器；CLOCK_MONOTONIC：相對(duì)時(shí)間類型，修改時(shí)鐘不影響定時(shí)器。
L35：設(shè)置定時(shí)器的值。
L44：阻塞等待定時(shí)器到期。返回值是未處理的到期次數(shù)。比如定時(shí)間隔為2秒，但過(guò)了10秒才去讀取，則讀取的值是5。
編譯運(yùn)行：編譯時(shí)要加rt庫(kù)(g++ -lrt timerfd.cc -o timerfd)
[root@localhost appTest]# ./timerfd 5 2 10printTime: current time:1357391736.146196 timer startedprintTime: current time:1357391741.153430 read: 1; total=1printTime: current time:1357391743.146550 read: 1; total=2printTime: current time:1357391745.151483 read: 1; total=3printTime: current time:1357391747.161155 read: 1; total=4printTime: current time:1357391749.153934 read: 1; total=5printTime: current time:1357391751.157309 read: 1; total=6printTime: current time:1357391753.158384 read: 1; total=7printTime: current time:1357391755.150470 read: 1; total=8printTime: current time:1357391757.150253 read: 1; total=9printTime: current time:1357391759.149954 read: 1; total=10[root@localhost appTest]#
第一個(gè)參數(shù)5為第一次定時(shí)器到期間隔，第二個(gè)參數(shù)2為定時(shí)器的間隔，第三個(gè)參數(shù)為定時(shí)器到期10次則退出。程序運(yùn)行(5+2*10)S退出。
詳細(xì)信息可以：man timerfd_create
eventfd涉及API：
#include <sys/eventfd.h> int eventfd(unsigned int initval, int flags);#include <sys/eventfd.h> int eventfd(unsigned int initval, int flags);
創(chuàng)建一個(gè)eventfd，這是一個(gè)計(jì)數(shù)器相關(guān)的fd，計(jì)數(shù)器不為零是有可讀事件發(fā)生，read以后計(jì)數(shù)器清零，write遞增計(jì)數(shù)器；返回的fd可以進(jìn)行如下操作：read、write、select(poll、epoll)、close。
這個(gè)函數(shù)會(huì)創(chuàng)建一個(gè)事件對(duì)象 (eventfd object), 用來(lái)實(shí)現(xiàn)，進(jìn)程(線程)間的等待/通知(wait/notify) 機(jī)制. 內(nèi)核會(huì)為這個(gè)對(duì)象維護(hù)一個(gè)64位的計(jì)數(shù)器(uint64_t)。并且使用第一個(gè)參數(shù)(initval)初始化這個(gè)計(jì)數(shù)器。調(diào)用這個(gè)函數(shù)就會(huì)返回一個(gè)新的文件描述符(event object)。2.6.27版本開(kāi)始可以按位設(shè)置第二個(gè)參數(shù)(flags)。有如下的一些宏可以使用：
lEFD_NONBLOCK
功能同open(2)的O_NONBLOCK，設(shè)置對(duì)象為非阻塞狀態(tài)，如果沒(méi)有設(shè)置這個(gè)狀態(tài)的話，read(2)讀eventfd,并且計(jì)數(shù)器的值為0 就一直堵塞在read調(diào)用當(dāng)中，要是設(shè)置了這個(gè)標(biāo)志， 就會(huì)返回一個(gè) EAGAIN 錯(cuò)誤(errno = EAGAIN)。效果也如同 額外調(diào)用select(2)達(dá)到的效果。
lEFD_CLOEXEC
這個(gè)標(biāo)識(shí)被設(shè)置的話，調(diào)用exec后會(huì)自動(dòng)關(guān)閉文件描述符，防止泄漏。如果是2.6.26或之前版本的內(nèi)核，flags 必須設(shè)置為0。
創(chuàng)建這個(gè)對(duì)象后，可以對(duì)其做如下操作：
1) write： 將緩沖區(qū)寫(xiě)入的8字節(jié)整形值加到內(nèi)核計(jì)數(shù)器上。
2) read： 讀取8字節(jié)值， 并把計(jì)數(shù)器重設(shè)為0. 如果調(diào)用read的時(shí)候計(jì)數(shù)器為0， 要是eventfd是阻塞的， read就一直阻塞在這里，否則就得到 一個(gè)EAGAIN錯(cuò)誤。如果buffer的長(zhǎng)度小于8那么read會(huì)失敗， 錯(cuò)誤代碼被設(shè)置成 EINVAL。
3) poll select epoll
4) close: 當(dāng)不需要eventfd的時(shí)候可以調(diào)用close關(guān)閉， 當(dāng)這個(gè)對(duì)象的所有句柄都被關(guān)閉的時(shí)候，內(nèi)核會(huì)釋放資源。 為什么不是close就直接釋放呢， 如果調(diào)用fork 創(chuàng)建
進(jìn)程的時(shí)候會(huì)復(fù)制這個(gè)句柄到新的進(jìn)程，并繼承所有的狀態(tài)。
l例子
#include <sys/eventfd.h>#include <unistd.h>#include <stdio.h>#include <stdint.h>#include <stdlib.h>#include <errno.h>#define handle_error(msg) /do { perror(msg); exit(1); } while (0)int main( int argc, char **argv ){uint64_t u;ssize_t s;5 int j;if ( argc < 2 ) {fprintf(stderr, "input in command argument");exit(1);}int efd;if ( (efd = eventfd(0, EFD_NONBLOCK)) == -1 )handle_error("eventfd failed");switch (fork()) {case 0:for( j = 1; j < argc; j ++ ) {printf("Child writing %s to efd/n", argv[j] );u = strtoull(argv[j], NULL, 0); /* analogesly atoi */s = write(efd, &u, sizeof(uint64_t));/*append u to counter */if ( s != sizeof(uint64_t) )handle_error("write efd failed");}printf("child completed write loop/n");exit(0);default:sleep (2);printf("parent about to read/n");s = read(efd, &u, sizeof(uint64_t));if ( s != sizeof(uint64_t) ) {if (errno = EAGAIN) {printf("Parent read value %d/n", s);return 1;}handle_error("parent read failed");}printf("parent read %d , %llu (0x%llx) from efd/n",s, (unsigned long long)u, (unsigned long long) u);exit(0);case -1:handle_error("fork ");}return 0;}#include <sys/eventfd.h>#include <unistd.h>#include <stdio.h>#include <stdint.h>#include <stdlib.h>#include <errno.h>#define handle_error(msg) /do { perror(msg); exit(1); } while (0)int main( int argc, char **argv ){uint64_t u;ssize_t s;5 int j;if ( argc < 2 ) {fprintf(stderr, "input in command argument");exit(1);}int efd;if ( (efd = eventfd(0, EFD_NONBLOCK)) == -1 )handle_error("eventfd failed");switch (fork()) {case 0:for( j = 1; j < argc; j ++ ) {printf("Child writing %s to efd/n", argv[j] );u = strtoull(argv[j], NULL, 0); /* analogesly atoi */s = write(efd, &u, sizeof(uint64_t));/*append u to counter */if ( s != sizeof(uint64_t) )handle_error("write efd failed");}printf("child completed write loop/n");exit(0);default:sleep (2);printf("parent about to read/n");s = read(efd, &u, sizeof(uint64_t));if ( s != sizeof(uint64_t) ) {if (errno = EAGAIN) {printf("Parent read value %d/n", s);return 1;}handle_error("parent read failed");}printf("parent read %d , %llu (0x%llx) from efd/n",s, (unsigned long long)u, (unsigned long long) u);exit(0);case -1:handle_error("fork ");}return 0;}以上所述是小編給大家介紹的Linux 新的API signalfd、timerfd、eventfd使用說(shuō)明，希望對(duì)大家有所幫助，如果大家有任何疑問(wèn)請(qǐng)給我留言，小編會(huì)及時(shí)回復(fù)大家的。在此也非常感謝大家對(duì)VEVB武林網(wǎng)網(wǎng)站的支持！
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