lib/poll-loop.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2010 Nicira Networks.
   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 #include "poll-loop.h"
  19 #include <assert.h>
  20 #include <errno.h>
  21 #include <inttypes.h>
  22 #include <poll.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include "backtrace.h"
  26 #include "coverage.h"
  27 #include "dynamic-string.h"
  28 #include "fatal-signal.h"
  29 #include "list.h"
  30 #include "timeval.h"
  31 #include "vlog.h"
  32
  33 VLOG_DEFINE_THIS_MODULE(poll_loop);
  34
  35 COVERAGE_DEFINE(poll_fd_wait);
  36 COVERAGE_DEFINE(poll_zero_timeout);
  37
  38 /* An event that will wake the following call to poll_block(). */
  39 struct poll_waiter {
  40     /* Set when the waiter is created. */
  41     struct list node;           /* Element in global waiters list. */
  42     int fd;                     /* File descriptor. */
  43     short int events;           /* Events to wait for (POLLIN, POLLOUT). */
  44     struct backtrace *backtrace; /* Optionally, event that created waiter. */
  45
  46     /* Set only when poll_block() is called. */
  47     struct pollfd *pollfd;      /* Pointer to element of the pollfds array. */
  48 };
  49
  50 /* All active poll waiters. */
  51 static struct list waiters = LIST_INITIALIZER(&waiters);
  52
  53 /* Number of elements in the waiters list. */
  54 static size_t n_waiters;
  55
  56 /* Max time to wait in next call to poll_block(), in milliseconds, or -1 to
  57  * wait forever. */
  58 static int timeout = -1;
  59
  60 /* Backtrace of 'timeout''s registration, if debugging is enabled. */
  61 static struct backtrace timeout_backtrace;
  62
  63 static struct poll_waiter *new_waiter(int fd, short int events);
  64
  65 /* Registers 'fd' as waiting for the specified 'events' (which should be POLLIN
  66  * or POLLOUT or POLLIN | POLLOUT).  The following call to poll_block() will
  67  * wake up when 'fd' becomes ready for one or more of the requested events.
  68  *
  69  * The event registration is one-shot: only the following call to poll_block()
  70  * is affected.  The event will need to be re-registered after poll_block() is
  71  * called if it is to persist. */
  72 struct poll_waiter *
  73 poll_fd_wait(int fd, short int events)
  74 {
  75     COVERAGE_INC(poll_fd_wait);
  76     return new_waiter(fd, events);
  77 }
  78
  79 /* The caller must ensure that 'msec' is not negative. */
  80 static void
  81 poll_timer_wait__(int msec)
  82 {
  83     if (timeout < 0 || msec < timeout) {
  84         timeout = msec;
  85         if (VLOG_IS_DBG_ENABLED()) {
  86             backtrace_capture(&timeout_backtrace);
  87         }
  88     }
  89 }
  90
  91 /* Causes the following call to poll_block() to block for no more than 'msec'
  92  * milliseconds.  If 'msec' is nonpositive, the following call to poll_block()
  93  * will not block at all.
  94  *
  95  * The timer registration is one-shot: only the following call to poll_block()
  96  * is affected.  The timer will need to be re-registered after poll_block() is
  97  * called if it is to persist. */
  98 void
  99 poll_timer_wait(long long int msec)
 100 {
 101     poll_timer_wait__(msec < 0 ? 0
 102                       : msec > INT_MAX ? INT_MAX
 103                       : msec);
 104 }
 105
 106 /* Causes the following call to poll_block() to wake up when the current time,
 107  * as returned by time_msec(), reaches 'msec' or later.  If 'msec' is earlier
 108  * than the current time, the following call to poll_block() will not block at
 109  * all.
 110  *
 111  * The timer registration is one-shot: only the following call to poll_block()
 112  * is affected.  The timer will need to be re-registered after poll_block() is
 113  * called if it is to persist. */
 114 void
 115 poll_timer_wait_until(long long int msec)
 116 {
 117     long long int now = time_msec();
 118     poll_timer_wait__(msec <= now ? 0
 119                       : msec < now + INT_MAX ? msec - now
 120                       : INT_MAX);
 121 }
 122
 123 /* Causes the following call to poll_block() to wake up immediately, without
 124  * blocking. */
 125 void
 126 poll_immediate_wake(void)
 127 {
 128     poll_timer_wait(0);
 129 }
 130
 131 static void PRINTF_FORMAT(2, 3)
 132 log_wakeup(const struct backtrace *backtrace, const char *format, ...)
 133 {
 134     struct ds ds;
 135     va_list args;
 136
 137     ds_init(&ds);
 138     va_start(args, format);
 139     ds_put_format_valist(&ds, format, args);
 140     va_end(args);
 141
 142     if (backtrace) {
 143         int i;
 144
 145         ds_put_char(&ds, ':');
 146         for (i = 0; i < backtrace->n_frames; i++) {
 147             ds_put_format(&ds, " 0x%"PRIxPTR, backtrace->frames[i]);
 148         }
 149     }
 150     VLOG_DBG("%s", ds_cstr(&ds));
 151     ds_destroy(&ds);
 152 }
 153
 154 /* Blocks until one or more of the events registered with poll_fd_wait()
 155  * occurs, or until the minimum duration registered with poll_timer_wait()
 156  * elapses, or not at all if poll_immediate_wake() has been called. */
 157 void
 158 poll_block(void)
 159 {
 160     static struct pollfd *pollfds;
 161     static size_t max_pollfds;
 162
 163     struct poll_waiter *pw, *next;
 164     int n_pollfds;
 165     int retval;
 166
 167     /* Register fatal signal events before actually doing any real work for
 168      * poll_block. */
 169     fatal_signal_wait();
 170
 171     if (max_pollfds < n_waiters) {
 172         max_pollfds = n_waiters;
 173         pollfds = xrealloc(pollfds, max_pollfds * sizeof *pollfds);
 174     }
 175
 176     n_pollfds = 0;
 177     LIST_FOR_EACH (pw, node, &waiters) {
 178         pw->pollfd = &pollfds[n_pollfds];
 179         pollfds[n_pollfds].fd = pw->fd;
 180         pollfds[n_pollfds].events = pw->events;
 181         pollfds[n_pollfds].revents = 0;
 182         n_pollfds++;
 183     }
 184
 185     if (!timeout) {
 186         COVERAGE_INC(poll_zero_timeout);
 187     }
 188     retval = time_poll(pollfds, n_pollfds, timeout);
 189     if (retval < 0) {
 190         static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
 191         VLOG_ERR_RL(&rl, "poll: %s", strerror(-retval));
 192     } else if (!retval && VLOG_IS_DBG_ENABLED()) {
 193         log_wakeup(&timeout_backtrace, "%d-ms timeout", timeout);
 194     }
 195
 196     LIST_FOR_EACH_SAFE (pw, next, node, &waiters) {
 197         if (pw->pollfd->revents && VLOG_IS_DBG_ENABLED()) {
 198             log_wakeup(pw->backtrace, "%s%s%s%s%s on fd %d",
 199                        pw->pollfd->revents & POLLIN ? "[POLLIN]" : "",
 200                        pw->pollfd->revents & POLLOUT ? "[POLLOUT]" : "",
 201                        pw->pollfd->revents & POLLERR ? "[POLLERR]" : "",
 202                        pw->pollfd->revents & POLLHUP ? "[POLLHUP]" : "",
 203                        pw->pollfd->revents & POLLNVAL ? "[POLLNVAL]" : "",
 204                        pw->fd);
 205         }
 206         poll_cancel(pw);
 207     }
 208
 209     timeout = -1;
 210     timeout_backtrace.n_frames = 0;
 211
 212     /* Handle any pending signals before doing anything else. */
 213     fatal_signal_run();
 214 }
 215
 216 /* Cancels the file descriptor event registered with poll_fd_wait() using 'pw',
 217  * the struct poll_waiter returned by that function.
 218  *
 219  * An event registered with poll_fd_wait() may be canceled from its time of
 220  * registration until the next call to poll_block().  At that point, the event
 221  * is automatically canceled by the system and its poll_waiter is freed. */
 222 void
 223 poll_cancel(struct poll_waiter *pw)
 224 {
 225     if (pw) {
 226         list_remove(&pw->node);
 227         free(pw->backtrace);
 228         free(pw);
 229         n_waiters--;
 230     }
 231 }
 232 \f
 233 /* Creates and returns a new poll_waiter for 'fd' and 'events'. */
 234 static struct poll_waiter *
 235 new_waiter(int fd, short int events)
 236 {
 237     struct poll_waiter *waiter = xzalloc(sizeof *waiter);
 238     assert(fd >= 0);
 239     waiter->fd = fd;
 240     waiter->events = events;
 241     if (VLOG_IS_DBG_ENABLED()) {
 242         waiter->backtrace = xmalloc(sizeof *waiter->backtrace);
 243         backtrace_capture(waiter->backtrace);
 244     }
 245     list_push_back(&waiters, &waiter->node);
 246     n_waiters++;
 247     return waiter;
 248 }