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