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/* |
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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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/* |
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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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|
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#include <sys/epoll.h> |
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|
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#define EV_EMASK_EPERM 0x80 |
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|
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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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/* |
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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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|
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oldmask = anfds [fd].emask; |
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anfds [fd].emask = nev; |
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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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return; |
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} |
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|
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fd_kill (EV_A_ fd); |
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|
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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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|
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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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|
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if (expect_false (epoll_epermcnt)) |
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timeout = 0.; |
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|
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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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|
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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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|
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return; |
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} |
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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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|
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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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/* |
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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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|
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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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/* |
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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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|
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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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|
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fd_event (EV_A_ fd, got); |
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} |
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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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|
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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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|
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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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|
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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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#ifdef EPOLL_CLOEXEC |
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backend_fd = epoll_create1 (EPOLL_CLOEXEC); |
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|
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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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|
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if (backend_fd < 0) |
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return 0; |
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|
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fcntl (backend_fd, F_SETFD, FD_CLOEXEC); |
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|
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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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|
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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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|
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return EVBACKEND_EPOLL; |
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} |
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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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|
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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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|
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while ((backend_fd = epoll_create (256)) < 0) |
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ev_syserr ("(libev) epoll_create"); |
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|
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fcntl (backend_fd, F_SETFD, FD_CLOEXEC); |
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|
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fd_rearm_all (EV_A); |
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} |
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|