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Edit File: ev_epoll.c
/* * libev epoll fd activity backend * * Copyright (c) 2007,2008,2009,2010,2011,2016,2017,2019 Marc Alexander Lehmann <libev@schmorp.de> * All rights reserved. * * Redistribution and use in source and binary forms, with or without modifica- * tion, are permitted provided that the following conditions are met: * * 1. Redistributions of source code must retain the above copyright notice, * this list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MER- * CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPE- * CIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTH- * ERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED * OF THE POSSIBILITY OF SUCH DAMAGE. * * Alternatively, the contents of this file may be used under the terms of * the GNU General Public License ("GPL") version 2 or any later version, * in which case the provisions of the GPL are applicable instead of * the above. If you wish to allow the use of your version of this file * only under the terms of the GPL and not to allow others to use your * version of this file under the BSD license, indicate your decision * by deleting the provisions above and replace them with the notice * and other provisions required by the GPL. If you do not delete the * provisions above, a recipient may use your version of this file under * either the BSD or the GPL. */ /* * general notes about epoll: * * a) epoll silently removes fds from the fd set. as nothing tells us * that an fd has been removed otherwise, we have to continually * "rearm" fds that we suspect *might* have changed (same * problem with kqueue, but much less costly there). * b) the fact that ADD != MOD creates a lot of extra syscalls due to a) * and seems not to have any advantage. * c) the inability to handle fork or file descriptors (think dup) * limits the applicability over poll, so this is not a generic * poll replacement. * d) epoll doesn't work the same as select with many file descriptors * (such as files). while not critical, no other advanced interface * seems to share this (rather non-unixy) limitation. * e) epoll claims to be embeddable, but in practise you never get * a ready event for the epoll fd (broken: <=2.6.26, working: >=2.6.32). * f) epoll_ctl returning EPERM means the fd is always ready. * * lots of "weird code" and complication handling in this file is due * to these design problems with epoll, as we try very hard to avoid * epoll_ctl syscalls for common usage patterns and handle the breakage * ensuing from receiving events for closed and otherwise long gone * file descriptors. */ #include <sys/epoll.h> #define EV_EMASK_EPERM 0x80 static void epoll_modify (EV_P_ int fd, int oev, int nev) { struct epoll_event ev; unsigned char oldmask; /* * we handle EPOLL_CTL_DEL by ignoring it here * on the assumption that the fd is gone anyways * if that is wrong, we have to handle the spurious * event in epoll_poll. * if the fd is added again, we try to ADD it, and, if that * fails, we assume it still has the same eventmask. */ if (!nev) return; oldmask = anfds [fd].emask; anfds [fd].emask = nev; /* store the generation counter in the upper 32 bits, the fd in the lower 32 bits */ ev.data.u64 = (uint64_t)(uint32_t)fd | ((uint64_t)(uint32_t)++anfds [fd].egen << 32); ev.events = (nev & EV_READ ? EPOLLIN : 0) | (nev & EV_WRITE ? EPOLLOUT : 0); if (ecb_expect_true (!epoll_ctl (backend_fd, oev && oldmask != nev ? EPOLL_CTL_MOD : EPOLL_CTL_ADD, fd, &ev))) return; if (ecb_expect_true (errno == ENOENT)) { /* if ENOENT then the fd went away, so try to do the right thing */ if (!nev) goto dec_egen; if (!epoll_ctl (backend_fd, EPOLL_CTL_ADD, fd, &ev)) return; } else if (ecb_expect_true (errno == EEXIST)) { /* EEXIST means we ignored a previous DEL, but the fd is still active */ /* if the kernel mask is the same as the new mask, we assume it hasn't changed */ if (oldmask == nev) goto dec_egen; if (!epoll_ctl (backend_fd, EPOLL_CTL_MOD, fd, &ev)) return; } else if (ecb_expect_true (errno == EPERM)) { /* EPERM means the fd is always ready, but epoll is too snobbish */ /* to handle it, unlike select or poll. */ anfds [fd].emask = EV_EMASK_EPERM; /* add fd to epoll_eperms, if not already inside */ if (!(oldmask & EV_EMASK_EPERM)) { array_needsize (int, epoll_eperms, epoll_epermmax, epoll_epermcnt + 1, array_needsize_noinit); epoll_eperms [epoll_epermcnt++] = fd; } return; } else assert (("libev: I/O watcher with invalid fd found in epoll_ctl", errno != EBADF && errno != ELOOP && errno != EINVAL)); fd_kill (EV_A_ fd); dec_egen: /* we didn't successfully call epoll_ctl, so decrement the generation counter again */ --anfds [fd].egen; } static void epoll_poll (EV_P_ ev_tstamp timeout) { int i; int eventcnt; if (ecb_expect_false (epoll_epermcnt)) timeout = EV_TS_CONST (0.); /* epoll wait times cannot be larger than (LONG_MAX - 999UL) / HZ msecs, which is below */ /* the default libev max wait time, however. */ EV_RELEASE_CB; eventcnt = epoll_wait (backend_fd, epoll_events, epoll_eventmax, EV_TS_TO_MSEC (timeout)); EV_ACQUIRE_CB; if (ecb_expect_false (eventcnt < 0)) { if (errno != EINTR) ev_syserr ("(libev) epoll_wait"); return; } for (i = 0; i < eventcnt; ++i) { struct epoll_event *ev = epoll_events + i; int fd = (uint32_t)ev->data.u64; /* mask out the lower 32 bits */ int want = anfds [fd].events; int got = (ev->events & (EPOLLOUT | EPOLLERR | EPOLLHUP) ? EV_WRITE : 0) | (ev->events & (EPOLLIN | EPOLLERR | EPOLLHUP) ? EV_READ : 0); /* * check for spurious notification. * this only finds spurious notifications on egen updates * other spurious notifications will be found by epoll_ctl, below * we assume that fd is always in range, as we never shrink the anfds array */ if (ecb_expect_false ((uint32_t)anfds [fd].egen != (uint32_t)(ev->data.u64 >> 32))) { /* recreate kernel state */ postfork |= 2; continue; } if (ecb_expect_false (got & ~want)) { anfds [fd].emask = want; /* * we received an event but are not interested in it, try mod or del * this often happens because we optimistically do not unregister fds * when we are no longer interested in them, but also when we get spurious * notifications for fds from another process. this is partially handled * above with the gencounter check (== our fd is not the event fd), and * partially here, when epoll_ctl returns an error (== a child has the fd * but we closed it). * note: for events such as POLLHUP, where we can't know whether it refers * to EV_READ or EV_WRITE, we might issue redundant EPOLL_CTL_MOD calls. */ ev->events = (want & EV_READ ? EPOLLIN : 0) | (want & EV_WRITE ? EPOLLOUT : 0); /* pre-2.6.9 kernels require a non-null pointer with EPOLL_CTL_DEL, */ /* which is fortunately easy to do for us. */ if (epoll_ctl (backend_fd, want ? EPOLL_CTL_MOD : EPOLL_CTL_DEL, fd, ev)) { postfork |= 2; /* an error occurred, recreate kernel state */ continue; } } fd_event (EV_A_ fd, got); } /* if the receive array was full, increase its size */ if (ecb_expect_false (eventcnt == epoll_eventmax)) { ev_free (epoll_events); epoll_eventmax = array_nextsize (sizeof (struct epoll_event), epoll_eventmax, epoll_eventmax + 1); epoll_events = (struct epoll_event *)ev_malloc (sizeof (struct epoll_event) * epoll_eventmax); } /* now synthesize events for all fds where epoll fails, while select works... */ for (i = epoll_epermcnt; i--; ) { int fd = epoll_eperms [i]; unsigned char events = anfds [fd].events & (EV_READ | EV_WRITE); if (anfds [fd].emask & EV_EMASK_EPERM && events) fd_event (EV_A_ fd, events); else { epoll_eperms [i] = epoll_eperms [--epoll_epermcnt]; anfds [fd].emask = 0; } } } static int epoll_epoll_create (void) { int fd; #if defined EPOLL_CLOEXEC && !defined __ANDROID__ fd = epoll_create1 (EPOLL_CLOEXEC); if (fd < 0 && (errno == EINVAL || errno == ENOSYS)) #endif { fd = epoll_create (256); if (fd >= 0) fcntl (fd, F_SETFD, FD_CLOEXEC); } return fd; } inline_size int epoll_init (EV_P_ int flags) { if ((backend_fd = epoll_epoll_create ()) < 0) return 0; backend_mintime = EV_TS_CONST (1e-3); /* epoll does sometimes return early, this is just to avoid the worst */ backend_modify = epoll_modify; backend_poll = epoll_poll; epoll_eventmax = 64; /* initial number of events receivable per poll */ epoll_events = (struct epoll_event *)ev_malloc (sizeof (struct epoll_event) * epoll_eventmax); return EVBACKEND_EPOLL; } inline_size void epoll_destroy (EV_P) { ev_free (epoll_events); array_free (epoll_eperm, EMPTY); } ecb_cold static void epoll_fork (EV_P) { close (backend_fd); while ((backend_fd = epoll_epoll_create ()) < 0) ev_syserr ("(libev) epoll_create"); fd_rearm_all (EV_A); }