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286 lines
9.7 KiB
C
286 lines
9.7 KiB
C
/*
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* libev epoll fd activity backend
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*
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* Copyright (c) 2007,2008,2009,2010,2011 Marc Alexander Lehmann <libev@schmorp.de>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without modifica-
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* tion, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
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* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MER-
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* CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
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* EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPE-
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* CIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
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* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTH-
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* ERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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* OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* Alternatively, the contents of this file may be used under the terms of
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* the GNU General Public License ("GPL") version 2 or any later version,
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* in which case the provisions of the GPL are applicable instead of
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* the above. If you wish to allow the use of your version of this file
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* only under the terms of the GPL and not to allow others to use your
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* version of this file under the BSD license, indicate your decision
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* by deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL. If you do not delete the
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* provisions above, a recipient may use your version of this file under
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* either the BSD or the GPL.
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*/
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/*
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* general notes about epoll:
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*
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* a) epoll silently removes fds from the fd set. as nothing tells us
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* that an fd has been removed otherwise, we have to continually
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* "rearm" fds that we suspect *might* have changed (same
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* problem with kqueue, but much less costly there).
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* b) the fact that ADD != MOD creates a lot of extra syscalls due to a)
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* and seems not to have any advantage.
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* c) the inability to handle fork or file descriptors (think dup)
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* limits the applicability over poll, so this is not a generic
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* poll replacement.
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* d) epoll doesn't work the same as select with many file descriptors
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* (such as files). while not critical, no other advanced interface
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* seems to share this (rather non-unixy) limitation.
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* e) epoll claims to be embeddable, but in practise you never get
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* a ready event for the epoll fd (broken: <=2.6.26, working: >=2.6.32).
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* f) epoll_ctl returning EPERM means the fd is always ready.
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*
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* lots of "weird code" and complication handling in this file is due
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* to these design problems with epoll, as we try very hard to avoid
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* epoll_ctl syscalls for common usage patterns and handle the breakage
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* ensuing from receiving events for closed and otherwise long gone
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* file descriptors.
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*/
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#include <sys/epoll.h>
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#define EV_EMASK_EPERM 0x80
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static void
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epoll_modify (EV_P_ int fd, int oev, int nev)
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{
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struct epoll_event ev;
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unsigned char oldmask;
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/*
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* we handle EPOLL_CTL_DEL by ignoring it here
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* on the assumption that the fd is gone anyways
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* if that is wrong, we have to handle the spurious
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* event in epoll_poll.
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* if the fd is added again, we try to ADD it, and, if that
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* fails, we assume it still has the same eventmask.
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*/
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if (!nev)
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return;
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oldmask = anfds [fd].emask;
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anfds [fd].emask = nev;
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/* store the generation counter in the upper 32 bits, the fd in the lower 32 bits */
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ev.data.u64 = (uint64_t)(uint32_t)fd
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| ((uint64_t)(uint32_t)++anfds [fd].egen << 32);
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ev.events = (nev & EV_READ ? EPOLLIN : 0)
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| (nev & EV_WRITE ? EPOLLOUT : 0);
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if (expect_true (!epoll_ctl (backend_fd, oev && oldmask != nev ? EPOLL_CTL_MOD : EPOLL_CTL_ADD, fd, &ev)))
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return;
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if (expect_true (errno == ENOENT))
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{
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/* if ENOENT then the fd went away, so try to do the right thing */
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if (!nev)
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goto dec_egen;
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if (!epoll_ctl (backend_fd, EPOLL_CTL_ADD, fd, &ev))
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return;
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}
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else if (expect_true (errno == EEXIST))
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{
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/* EEXIST means we ignored a previous DEL, but the fd is still active */
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/* if the kernel mask is the same as the new mask, we assume it hasn't changed */
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if (oldmask == nev)
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goto dec_egen;
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if (!epoll_ctl (backend_fd, EPOLL_CTL_MOD, fd, &ev))
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return;
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}
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else if (expect_true (errno == EPERM))
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{
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/* EPERM means the fd is always ready, but epoll is too snobbish */
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/* to handle it, unlike select or poll. */
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anfds [fd].emask = EV_EMASK_EPERM;
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/* add fd to epoll_eperms, if not already inside */
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if (!(oldmask & EV_EMASK_EPERM))
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{
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array_needsize (int, epoll_eperms, epoll_epermmax, epoll_epermcnt + 1, EMPTY2);
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epoll_eperms [epoll_epermcnt++] = fd;
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}
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return;
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}
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fd_kill (EV_A_ fd);
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dec_egen:
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/* we didn't successfully call epoll_ctl, so decrement the generation counter again */
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--anfds [fd].egen;
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}
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static void
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epoll_poll (EV_P_ ev_tstamp timeout)
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{
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int i;
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int eventcnt;
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if (expect_false (epoll_epermcnt))
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timeout = 0.;
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/* epoll wait times cannot be larger than (LONG_MAX - 999UL) / HZ msecs, which is below */
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/* the default libev max wait time, however. */
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EV_RELEASE_CB;
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eventcnt = epoll_wait (backend_fd, epoll_events, epoll_eventmax, timeout * 1e3);
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EV_ACQUIRE_CB;
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if (expect_false (eventcnt < 0))
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{
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if (errno != EINTR)
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ev_syserr ("(libev) epoll_wait");
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return;
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}
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for (i = 0; i < eventcnt; ++i)
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{
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struct epoll_event *ev = epoll_events + i;
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int fd = (uint32_t)ev->data.u64; /* mask out the lower 32 bits */
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int want = anfds [fd].events;
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int got = (ev->events & (EPOLLOUT | EPOLLERR | EPOLLHUP) ? EV_WRITE : 0)
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| (ev->events & (EPOLLIN | EPOLLERR | EPOLLHUP) ? EV_READ : 0);
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/*
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* check for spurious notification.
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* this only finds spurious notifications on egen updates
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* other spurious notifications will be found by epoll_ctl, below
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* we assume that fd is always in range, as we never shrink the anfds array
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*/
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if (expect_false ((uint32_t)anfds [fd].egen != (uint32_t)(ev->data.u64 >> 32)))
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{
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/* recreate kernel state */
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postfork |= 2;
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continue;
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}
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if (expect_false (got & ~want))
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{
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anfds [fd].emask = want;
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/*
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* we received an event but are not interested in it, try mod or del
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* this often happens because we optimistically do not unregister fds
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* when we are no longer interested in them, but also when we get spurious
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* notifications for fds from another process. this is partially handled
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* above with the gencounter check (== our fd is not the event fd), and
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* partially here, when epoll_ctl returns an error (== a child has the fd
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* but we closed it).
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*/
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ev->events = (want & EV_READ ? EPOLLIN : 0)
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| (want & EV_WRITE ? EPOLLOUT : 0);
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/* pre-2.6.9 kernels require a non-null pointer with EPOLL_CTL_DEL, */
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/* which is fortunately easy to do for us. */
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if (epoll_ctl (backend_fd, want ? EPOLL_CTL_MOD : EPOLL_CTL_DEL, fd, ev))
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{
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postfork |= 2; /* an error occurred, recreate kernel state */
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continue;
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}
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}
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fd_event (EV_A_ fd, got);
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}
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/* if the receive array was full, increase its size */
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if (expect_false (eventcnt == epoll_eventmax))
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{
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ev_free (epoll_events);
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epoll_eventmax = array_nextsize (sizeof (struct epoll_event), epoll_eventmax, epoll_eventmax + 1);
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epoll_events = (struct epoll_event *)ev_malloc (sizeof (struct epoll_event) * epoll_eventmax);
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}
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/* now synthesize events for all fds where epoll fails, while select works... */
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for (i = epoll_epermcnt; i--; )
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{
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int fd = epoll_eperms [i];
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unsigned char events = anfds [fd].events & (EV_READ | EV_WRITE);
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if (anfds [fd].emask & EV_EMASK_EPERM && events)
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fd_event (EV_A_ fd, events);
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else
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{
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epoll_eperms [i] = epoll_eperms [--epoll_epermcnt];
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anfds [fd].emask = 0;
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}
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}
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}
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inline_size
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int
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epoll_init (EV_P_ int flags)
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{
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#if defined EPOLL_CLOEXEC && !defined __ANDROID__
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backend_fd = epoll_create1 (EPOLL_CLOEXEC);
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if (backend_fd < 0 && (errno == EINVAL || errno == ENOSYS))
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#endif
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backend_fd = epoll_create (256);
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if (backend_fd < 0)
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return 0;
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fcntl (backend_fd, F_SETFD, FD_CLOEXEC);
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backend_mintime = 1e-3; /* epoll does sometimes return early, this is just to avoid the worst */
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backend_modify = epoll_modify;
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backend_poll = epoll_poll;
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epoll_eventmax = 64; /* initial number of events receivable per poll */
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epoll_events = (struct epoll_event *)ev_malloc (sizeof (struct epoll_event) * epoll_eventmax);
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return EVBACKEND_EPOLL;
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}
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inline_size
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void
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epoll_destroy (EV_P)
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{
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ev_free (epoll_events);
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array_free (epoll_eperm, EMPTY);
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}
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inline_size
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void
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epoll_fork (EV_P)
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{
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close (backend_fd);
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while ((backend_fd = epoll_create (256)) < 0)
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ev_syserr ("(libev) epoll_create");
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fcntl (backend_fd, F_SETFD, FD_CLOEXEC);
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fd_rearm_all (EV_A);
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}
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