lib/latch-unix.c

   1 /*
   2  * Copyright (c) 2013 Nicira, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #include <config.h>
  18
  19 #include "latch.h"
  20 #include <errno.h>
  21 #include <poll.h>
  22 #include <unistd.h>
  23 #include "openvswitch/poll-loop.h"
  24 #include "socket-util.h"
  25
  26 /* Initializes 'latch' as initially unset. */
  27 void
  28 latch_init(struct latch *latch)
  29 {
  30     xpipe_nonblocking(latch->fds);
  31 }
  32
  33 /* Destroys 'latch'. */
  34 void
  35 latch_destroy(struct latch *latch)
  36 {
  37     close(latch->fds[0]);
  38     close(latch->fds[1]);
  39 }
  40
  41 /* Resets 'latch' to the unset state.  Returns true if 'latch' was previously
  42  * set, false otherwise. */
  43 bool
  44 latch_poll(struct latch *latch)
  45 {
  46     char buffer[_POSIX_PIPE_BUF];
  47
  48     return read(latch->fds[0], buffer, sizeof buffer) > 0;
  49 }
  50
  51 /* Sets 'latch'.
  52  *
  53  * Calls are not additive: a single latch_poll() clears out any number of
  54  * latch_set(). */
  55 void
  56 latch_set(struct latch *latch)
  57 {
  58     ignore(write(latch->fds[1], "", 1));
  59 }
  60
  61 /* Returns true if 'latch' is set, false otherwise.  Does not reset 'latch'
  62  * to the unset state. */
  63 bool
  64 latch_is_set(const struct latch *latch)
  65 {
  66     struct pollfd pfd;
  67     int retval;
  68
  69     pfd.fd = latch->fds[0];
  70     pfd.events = POLLIN;
  71     do {
  72         retval = poll(&pfd, 1, 0);
  73     } while (retval < 0 && errno == EINTR);
  74
  75     return pfd.revents & POLLIN;
  76 }
  77
  78 /* Causes the next poll_block() to wake up when 'latch' is set.
  79  *
  80  * ('where' is used in debug logging.  Commonly one would use latch_wait() to
  81  * automatically provide the caller's source file and line number for
  82  * 'where'.) */
  83 void
  84 latch_wait_at(const struct latch *latch, const char *where)
  85 {
  86     poll_fd_wait_at(latch->fds[0], POLLIN, where);
  87 }