EPOLL 7 2021

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EPOLL

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epoll - I/O äºä»¶éç¥è®¾æ½

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#include <sys/epoll.h>

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	•		å´è¶£åè¡¨ï¼interest listï¼ææ¶ä¹ç§°ä¸º epoll éï¼epoll setï¼ï¼ï¼è¿ç¨æ³¨åäºâçæ§å´è¶£âçæä»¶æè¿°ç¬¦çéåã
	•		å°±ç»ªåè¡¨ï¼ready listï¼ï¼âåå¤å¥½âè¿è¡ I/O çæä»¶æè¿°ç¬¦çéåãå°±ç»ªåè¡¨æ¯å´è¶£åè¡¨ä¸çæä»¶æè¿°ç¬¦çå- éï¼æèæ´åç¡®å°è¯´ï¼æ¯å¶å¼ç¨çéåï¼ãåæ ¸ä¼æ ¹æ®è¿äºæä»¶æè¿°ç¬¦ä¸ç I/O æ´»å¨å¨æå°å¡«åå°±ç»ªåè¡¨ã

ä¸åç³»ç»è°ç¨å¯ç¨äºåå»ºåç®¡ç epoll å®ä¾ï¼

	•		epoll_create(2) ä¼åå»ºä¸ä¸ªæ°ç epoll å®ä¾ï¼å¹¶è¿åä¸ä¸ªæåè¯¥å®ä¾çæä»¶æè¿°ç¬¦ãï¼ææ°ç epoll_create1(2) æ©å±äº epoll_create(2) çåè½ãï¼
	•		epoll_ctl(2) è½å epoll å®ä¾çå´è¶£åè¡¨ä¸- æ·»å é¡¹ç®ï¼æ³¨åå¯¹ç¹å®æä»¶æè¿°ç¬¦çå´è¶£ã
	•		epoll_wait(2) ä¼çå¾ I/O äºä»¶ï¼å¦æå½åæ²¡æäºä»¶å¯ç¨ï¼åé»å¡è°ç¨å®ççº¿ç¨ãï¼æ¤ç³»ç»è°ç¨å¯è¢«çä½ä» epoll å®ä¾çå°±ç»ªåè¡¨ä¸è·åé¡¹ç®ãï¼

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	1.		è¯»åæ¹å¨ epoll å®ä¾ä¸æ³¨åä»£è¡¨ç®¡éè¯»åç«¯ï¼rfdï¼çæä»¶æè¿°ç¬¦ã
	2.		åå¥æ¹å¨ç®¡éçåå¥ç«¯åå¥ 2 kB çæ°æ®ã
	3.		è¯»åæ¹è°ç¨ epoll_wait(2)ï¼ rfd ä½ä¸ºä¸ä¸ªå°±ç»ªçæä»¶æè¿°ç¬¦è¢«è¿åã
	4.		è¯»åæ¹åªä» rfd ä¸è¯»å 1 kB çæ°æ®ã
	5.		è¯»åæ¹åæ¬¡è°ç¨ epoll_wait(2)ã

	a)		ä½¿ç¨éé»å¡çæä»¶æè¿°ç¬¦ï¼
	b)		åªå¨ read(2) æ write(2) è¿å EAGAIN ååçå¾æ°çäºä»¶ã

å³ä½¿æ¯è¾¹ç¼è§¦åç epollï¼å¨æ¶å°å¤ä¸ªæ°æ®åæ¶ä¹å¯è½äº§çå¤ä¸ªäºä»¶ï¼å æ- ¤è°ç¨èå¯ä»¥æå® EPOLLONESHOT æ å¿ä½ï¼åè¯ epoll å¨èªå·±ç¨ epoll_wait(2)æ¶å°äºä»¶åç¦ç¨ç¸å³çæä»¶æè¿°ç¬¦ãå½æå®äº EPOLLONESHOT æ å¿ä½æ¶ï¼è°ç¨èå¯ä½¿ç¨epoll_ctl(2) ä¸ EPOLL_CTL_MOD æ å¿ä½éè£ï¼rearmï¼ä¸ä¸ªè¢«ç¦ç¨çæä»¶æè¿°ç¬¦ï¼è¿æ¯è°ç¨èèä¸æ¯ epoll çè´£ä»»ã

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/proc æ¥å£

ä»¥ä¸æ¥å£å¯ä»¥ç¨æ¥éå¶ epoll æ¶èçåæ ¸ååçéã
/proc/sys/fs/epoll/max_user_watches ï¼ä» Linux 2.6.28 å¼å§ï¼

ç¤ºä¾ï¼å»ºè®®çä½¿ç¨ epoll çæ¹å¼

#define MAX_EVENTS 10
struct epoll_event ev, events[MAX_EVENTS];
int listen_sock, conn_sock, nfds, epollfd;

/* Code to set up listening socket, 'listen_sock',
(socket(), bind(), listen()) omitted. */

epollfd = epoll_create1(0);
if (epollfd == -1) {
perror("epoll_create1");
exit(EXIT_FAILURE);
}

ev.events = EPOLLIN;
ev.data.fd = listen_sock;
if (epoll_ctl(epollfd, EPOLL_CTL_ADD, listen_sock, &ev) == -1) {
perror("epoll_ctl: listen_sock");
exit(EXIT_FAILURE);
}

for (;;) {
nfds = epoll_wait(epollfd, events, MAX_EVENTS, -1);
if (nfds == -1) {
perror("epoll_wait");
exit(EXIT_FAILURE);
}

for (n = 0; n < nfds; ++n) {
if (events[n].data.fd == listen_sock) {
conn_sock = accept(listen_sock,
(struct sockaddr *) &addr, &addrlen);
if (conn_sock == -1) {
perror("accept");
exit(EXIT_FAILURE);
}
setnonblocking(conn_sock);
ev.events = EPOLLIN | EPOLLET;
ev.data.fd = conn_sock;
if (epoll_ctl(epollfd, EPOLL_CTL_ADD, conn_sock,
&ev) == -1) {
perror("epoll_ctl: conn_sock");
exit(EXIT_FAILURE);
}
} else {
do_use_fd(events[n].data.fd);
}
}
}

å½ä½ä¸ºè¾¹ç¼è§¦åçæ¥å£ä½¿ç¨æ¶ï¼åºäºæ§è½èèï¼å¯å¨æ·»åæä»¶æè¿°ç¬¦ï¼EPOLL_CTL_ADDï¼æ¶æå® (EPOLLIN|EPOLLOUT)ãè¿æ ·å¯ä»¥é¿ååå¤è°ç¨ epoll_ctl(2) ä¸EPOLL_CTL_MOD å¨ EPOLLIN å EPOLLOUT ä¹é´æ¥ååæ¢ã

epoll åé®

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æä»¶æè¿°ç¬¦çæ°å¼åæå¼æä»¶æè¿°ï¼open file descriptionï¼åç§°âopen file handleâï¼åæ ¸å¯¹æå¼çæä»¶çåé¨è¡¨ç¤ºï¼çç»åã

ä½ å¯è½ä¼å¾å° EEXISTãç¶èï¼å¨åä¸ä¸ªepollå®ä¾ä¸æ·»å éå¤çï¼dup(2),dup2(2), fcntl(2) F_DUPFDï¼æä»¶æè¿°ç¬¦æ¯å¯è½çãå¦æéå¤çæä»¶æè¿°ç¬¦æ¯ç¨ä¸åçäºä»¶æ©çï¼events maskï¼æ³¨åçï¼é£ä¹è¿ä¼æä¸ºè¿æ»¤äºä»¶çä¸ä¸ªå®ç¨æå·§ã

epoll æä»¶æè¿°ç¬¦æ¬èº« poll/epoll/selectable åï¼

epoll_ctl(2) è°ç¨ä¼å¤±è´¥ï¼EINVALï¼ãä½ä½ å¯ä»¥å°ä¸ä¸ª epoll æä»¶æè¿°ç¬¦æ·»å å°å¦ä¸ä¸ª epoll æä»¶æè¿°ç¬¦éåä¸ã

ä¼ï¼ä½è¦æ³¨æå ç¹ãæä»¶æè¿°ç¬¦æ¯å¯¹æå¼æä»¶æè¿°ï¼open file descriptionï¼çå¼ç¨ï¼è§ open(2)ï¼ãæ¯å½éè¿ dup(2), dup2(2), fcntl(2) F_DUPFD,æ fork(2) å¤å¶æä¸ªæä»¶æè¿°ç¬¦æ¶ï¼é½ä¼åå»ºä¸ä¸ªæ°çæä»¶æè¿°ç¬¦ï¼å¼ç¨åä¸ä¸ªæå¼æä»¶æè¿°ãä¸ä¸ªæå¼æä»¶æè¿°ä¼å¨ææå¼ç¨å®çæä»¶æè¿°ç¬¦è¢«å³é- ä¹åä¸ç´åå¨ã

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epoll API å¨ Linux åæ ¸2.5.44ä¸å¼å¥ã2.3.2çæ¬ç glibc å å¥äºå¯¹å¶çæ¯æã

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epoll API æ¯ Linux ç¹æçãå¶ä»çä¸äºç³»ç»ä¹æä¾ç±»ä¼¼çæºå¶ï¼ä¾å¦ FreeBSDæ kqueueï¼ Solaris æ /dev/pollã

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å¯ä»¥éè¿è¿ç¨å¯¹åºç /proc/[pid]/fdinfo ç®å½ä¸ç epoll æä»¶æè¿°ç¬¦æ¡ç®æ¥çepoll æä»¶æè¿°ç¬¦æçè§çæä»¶æè¿°ç¬¦çéåãè¯¦æè§ proc(5)ã

kcmp(2) ç KCMP_EPOLL_TFD æä½å¯ä»¥ç¨æ¥æ£æ¥ä¸ä¸ª epoll å®ä¾ä¸æ¯å¦å- å¨æä¸ªæä»¶æè¿°ç¬¦ã

å¦è¯·åé

epoll_create(2), epoll_create1(2), epoll_ctl(2), epoll_wait(2), poll(2), select(2)

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