lib/poll-loop.c

   1 /*
   2  * Copyright (c) 2008, 2009 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 <poll.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include "backtrace.h"
  25 #include "coverage.h"
  26 #include "dynamic-string.h"
  27 #include "list.h"
  28 #include "timeval.h"
  29
  30 #define THIS_MODULE VLM_poll_loop
  31 #include "vlog.h"
  32
  33 /* An event that will wake the following call to poll_block(). */
  34 struct poll_waiter {
  35     /* Set when the waiter is created. */
  36     struct list node;           /* Element in global waiters list. */
  37     int fd;                     /* File descriptor. */
  38     short int events;           /* Events to wait for (POLLIN, POLLOUT). */
  39     poll_fd_func *function;     /* Callback function, if any, or null. */
  40     void *aux;                  /* Argument to callback function. */
  41     struct backtrace *backtrace; /* Optionally, event that created waiter. */
  42
  43     /* Set only when poll_block() is called. */
  44     struct pollfd *pollfd;      /* Pointer to element of the pollfds array
  45                                    (null if added from a callback). */
  46 };
  47
  48 /* All active poll waiters. */
  49 static struct list waiters = LIST_INITIALIZER(&waiters);
  50
  51 /* Number of elements in the waiters list. */
  52 static size_t n_waiters;
  53
  54 /* Max time to wait in next call to poll_block(), in milliseconds, or -1 to
  55  * wait forever. */
  56 static int timeout = -1;
  57
  58 /* Backtrace of 'timeout''s registration, if debugging is enabled. */
  59 static struct backtrace timeout_backtrace;
  60
  61 /* Callback currently running, to allow verifying that poll_cancel() is not
  62  * being called on a running callback. */
  63 #ifndef NDEBUG
  64 static struct poll_waiter *running_cb;
  65 #endif
  66
  67 static struct poll_waiter *new_waiter(int fd, short int events);
  68
  69 /* Registers 'fd' as waiting for the specified 'events' (which should be POLLIN
  70  * or POLLOUT or POLLIN | POLLOUT).  The following call to poll_block() will
  71  * wake up when 'fd' becomes ready for one or more of the requested events.
  72  *
  73  * The event registration is one-shot: only the following call to poll_block()
  74  * is affected.  The event will need to be re-registered after poll_block() is
  75  * called if it is to persist. */
  76 struct poll_waiter *
  77 poll_fd_wait(int fd, short int events)
  78 {
  79     COVERAGE_INC(poll_fd_wait);
  80     return new_waiter(fd, events);
  81 }
  82
  83 /* Causes the following call to poll_block() to block for no more than 'msec'
  84  * milliseconds.  If 'msec' is nonpositive, the following call to poll_block()
  85  * will not block at all.
  86  *
  87  * The timer registration is one-shot: only the following call to poll_block()
  88  * is affected.  The timer will need to be re-registered after poll_block() is
  89  * called if it is to persist. */
  90 void
  91 poll_timer_wait(int msec)
  92 {
  93     if (timeout < 0 || msec < timeout) {
  94         timeout = MAX(0, msec);
  95         if (VLOG_IS_DBG_ENABLED()) {
  96             backtrace_capture(&timeout_backtrace);
  97         }
  98     }
  99 }
 100
 101 /* Causes the following call to poll_block() to wake up immediately, without
 102  * blocking. */
 103 void
 104 poll_immediate_wake(void)
 105 {
 106     poll_timer_wait(0);
 107 }
 108
 109 static void PRINTF_FORMAT(2, 3)
 110 log_wakeup(const struct backtrace *backtrace, const char *format, ...)
 111 {
 112     struct ds ds;
 113     va_list args;
 114
 115     ds_init(&ds);
 116     va_start(args, format);
 117     ds_put_format_valist(&ds, format, args);
 118     va_end(args);
 119
 120     if (backtrace) {
 121         int i;
 122
 123         ds_put_char(&ds, ':');
 124         for (i = 0; i < backtrace->n_frames; i++) {
 125             ds_put_format(&ds, " 0x%x", backtrace->frames[i]);
 126         }
 127     }
 128     VLOG_DBG("%s", ds_cstr(&ds));
 129     ds_destroy(&ds);
 130 }
 131
 132 /* Blocks until one or more of the events registered with poll_fd_wait()
 133  * occurs, or until the minimum duration registered with poll_timer_wait()
 134  * elapses, or not at all if poll_immediate_wake() has been called.
 135  *
 136  * Also executes any autonomous subroutines registered with poll_fd_callback(),
 137  * if their file descriptors have become ready. */
 138 void
 139 poll_block(void)
 140 {
 141     static struct pollfd *pollfds;
 142     static size_t max_pollfds;
 143
 144     struct poll_waiter *pw;
 145     struct list *node;
 146     int n_pollfds;
 147     int retval;
 148
 149     assert(!running_cb);
 150     if (max_pollfds < n_waiters) {
 151         max_pollfds = n_waiters;
 152         pollfds = xrealloc(pollfds, max_pollfds * sizeof *pollfds);
 153     }
 154
 155     n_pollfds = 0;
 156     LIST_FOR_EACH (pw, struct poll_waiter, node, &waiters) {
 157         pw->pollfd = &pollfds[n_pollfds];
 158         pollfds[n_pollfds].fd = pw->fd;
 159         pollfds[n_pollfds].events = pw->events;
 160         pollfds[n_pollfds].revents = 0;
 161         n_pollfds++;
 162     }
 163
 164     if (!timeout) {
 165         COVERAGE_INC(poll_zero_timeout);
 166     }
 167     retval = time_poll(pollfds, n_pollfds, timeout);
 168     if (retval < 0) {
 169         static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
 170         VLOG_ERR_RL(&rl, "poll: %s", strerror(-retval));
 171     } else if (!retval && VLOG_IS_DBG_ENABLED()) {
 172         log_wakeup(&timeout_backtrace, "%d-ms timeout", timeout);
 173     }
 174
 175     for (node = waiters.next; node != &waiters; ) {
 176         pw = CONTAINER_OF(node, struct poll_waiter, node);
 177         if (!pw->pollfd || !pw->pollfd->revents) {
 178             if (pw->function) {
 179                 node = node->next;
 180                 continue;
 181             }
 182         } else {
 183             if (VLOG_IS_DBG_ENABLED()) {
 184                 log_wakeup(pw->backtrace, "%s%s%s%s%s on fd %d",
 185                            pw->pollfd->revents & POLLIN ? "[POLLIN]" : "",
 186                            pw->pollfd->revents & POLLOUT ? "[POLLOUT]" : "",
 187                            pw->pollfd->revents & POLLERR ? "[POLLERR]" : "",
 188                            pw->pollfd->revents & POLLHUP ? "[POLLHUP]" : "",
 189                            pw->pollfd->revents & POLLNVAL ? "[POLLNVAL]" : "",
 190                            pw->fd);
 191             }
 192
 193             if (pw->function) {
 194 #ifndef NDEBUG
 195                 running_cb = pw;
 196 #endif
 197                 pw->function(pw->fd, pw->pollfd->revents, pw->aux);
 198 #ifndef NDEBUG
 199                 running_cb = NULL;
 200 #endif
 201             }
 202         }
 203         node = node->next;
 204         poll_cancel(pw);
 205     }
 206
 207     timeout = -1;
 208     timeout_backtrace.n_frames = 0;
 209 }
 210
 211 /* Registers 'function' to be called with argument 'aux' by poll_block() when
 212  * 'fd' becomes ready for one of the events in 'events', which should be POLLIN
 213  * or POLLOUT or POLLIN | POLLOUT.
 214  *
 215  * The callback registration persists until the event actually occurs.  At that
 216  * point, it is automatically de-registered.  The callback function must
 217  * re-register the event by calling poll_fd_callback() again within the
 218  * callback, if it wants to be called back again later. */
 219 struct poll_waiter *
 220 poll_fd_callback(int fd, short int events, poll_fd_func *function, void *aux)
 221 {
 222     struct poll_waiter *pw = new_waiter(fd, events);
 223     pw->function = function;
 224     pw->aux = aux;
 225     return pw;
 226 }
 227
 228 /* Cancels the file descriptor event registered with poll_fd_wait() or
 229  * poll_fd_callback().  'pw' must be the struct poll_waiter returned by one of
 230  * those functions.
 231  *
 232  * An event registered with poll_fd_wait() may be canceled from its time of
 233  * registration until the next call to poll_block().  At that point, the event
 234  * is automatically canceled by the system and its poll_waiter is freed.
 235  *
 236  * An event registered with poll_fd_callback() may be canceled from its time of
 237  * registration until its callback is actually called.  At that point, the
 238  * event is automatically canceled by the system and its poll_waiter is
 239  * freed. */
 240 void
 241 poll_cancel(struct poll_waiter *pw)
 242 {
 243     if (pw) {
 244         assert(pw != running_cb);
 245         list_remove(&pw->node);
 246         free(pw->backtrace);
 247         free(pw);
 248         n_waiters--;
 249     }
 250 }
 251 \f
 252 /* Creates and returns a new poll_waiter for 'fd' and 'events'. */
 253 static struct poll_waiter *
 254 new_waiter(int fd, short int events)
 255 {
 256     struct poll_waiter *waiter = xcalloc(1, sizeof *waiter);
 257     assert(fd >= 0);
 258     waiter->fd = fd;
 259     waiter->events = events;
 260     if (VLOG_IS_DBG_ENABLED()) {
 261         waiter->backtrace = xmalloc(sizeof *waiter->backtrace);
 262         backtrace_capture(waiter->backtrace);
 263     }
 264     list_push_back(&waiters, &waiter->node);
 265     n_waiters++;
 266     return waiter;
 267 }