before port to libev

libev/ev_epoll.c

@@ -0,0 +1,285 @@
+/*
+ * libev epoll fd activity backend
+ *
+ * Copyright (c) 2007,2008,2009,2010,2011 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 (expect_true (!epoll_ctl (backend_fd, oev && oldmask != nev ? EPOLL_CTL_MOD : EPOLL_CTL_ADD, fd, &ev)))
+    return;
+
+  if (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 (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 (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, EMPTY2);
+          epoll_eperms [epoll_epermcnt++] = fd;
+        }
+
+      return;
+    }
+
+  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 (expect_false (epoll_epermcnt))
+    timeout = 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, timeout * 1e3);
+  EV_ACQUIRE_CB;
+
+  if (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 (expect_false ((uint32_t)anfds [fd].egen != (uint32_t)(ev->data.u64 >> 32)))
+        {
+          /* recreate kernel state */
+          postfork |= 2;
+          continue;
+        }
+
+      if (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).
+           */
+          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 (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;
+        }
+    }
+}
+
+inline_size
+int
+epoll_init (EV_P_ int flags)
+{
+#if defined EPOLL_CLOEXEC && !defined __ANDROID__
+  backend_fd = epoll_create1 (EPOLL_CLOEXEC);
+
+  if (backend_fd < 0 && (errno == EINVAL || errno == ENOSYS))
+#endif
+    backend_fd = epoll_create (256);
+
+  if (backend_fd < 0)
+    return 0;
+
+  fcntl (backend_fd, F_SETFD, FD_CLOEXEC);
+
+  backend_mintime = 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);
+}
+
+inline_size
+void
+epoll_fork (EV_P)
+{
+  close (backend_fd);
+
+  while ((backend_fd = epoll_create (256)) < 0)
+    ev_syserr ("(libev) epoll_create");
+
+  fcntl (backend_fd, F_SETFD, FD_CLOEXEC);
+
+  fd_rearm_all (EV_A);
+}
+