code.delx.au - pulseaudio/blob - src/pulsecore/lock-autospawn.c

   1 /***
   2   This file is part of PulseAudio.
   3
   4   Copyright 2008 Lennart Poettering
   5
   6   PulseAudio is free software; you can redistribute it and/or modify
   7   it under the terms of the GNU Lesser General Public License as published
   8   by the Free Software Foundation; either version 2.1 of the License,
   9   or (at your option) any later version.
  10
  11   PulseAudio is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with PulseAudio; if not, write to the Free Software
  18   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
  19   USA.
  20 ***/
  21
  22 #ifdef HAVE_CONFIG_H
  23 #include <config.h>
  24 #endif
  25
  26 #include <errno.h>
  27 #include <string.h>
  28 #include <signal.h>
  29
  30 #ifdef HAVE_PTHREAD
  31 #include <pthread.h>
  32 #endif
  33
  34 #include <pulse/gccmacro.h>
  35 #include <pulse/xmalloc.h>
  36
  37 #include <pulsecore/i18n.h>
  38 #include <pulsecore/poll.h>
  39 #include <pulsecore/mutex.h>
  40 #include <pulsecore/thread.h>
  41 #include <pulsecore/core-util.h>
  42
  43 #include "lock-autospawn.h"
  44
  45 /* So, why do we have this complex code here with threads and pipes
  46  * and stuff? For two reasons: POSIX file locks are per-process, not
  47  * per-file descriptor. That means that two contexts within the same
  48  * process that try to create the autospawn lock might end up assuming
  49  * they both managed to lock the file. And then, POSIX locking
  50  * operations are synchronous. If two contexts run from the same event
  51  * loop it must be made sure that they do not block each other, but
  52  * that the locking operation can happen asynchronously. */
  53
  54 #define AUTOSPAWN_LOCK "autospawn.lock"
  55
  56 static pa_mutex *mutex;
  57
  58 static unsigned n_ref = 0;
  59 static int lock_fd = -1;
  60 static pa_mutex *lock_fd_mutex = NULL;
  61 static pa_thread *thread = NULL;
  62 static int pipe_fd[2] = { -1, -1 };
  63
  64 static enum {
  65     STATE_IDLE,
  66     STATE_OWNING,
  67     STATE_TAKEN,
  68     STATE_FAILED
  69 } state = STATE_IDLE;
  70
  71 static void destroy_mutex(void) PA_GCC_DESTRUCTOR;
  72
  73 static int ref(void) {
  74
  75     if (n_ref > 0) {
  76
  77         pa_assert(pipe_fd[0] >= 0);
  78         pa_assert(pipe_fd[1] >= 0);
  79         pa_assert(lock_fd_mutex);
  80
  81         n_ref++;
  82
  83         return 0;
  84     }
  85
  86     pa_assert(!lock_fd_mutex);
  87     pa_assert(state == STATE_IDLE);
  88     pa_assert(lock_fd < 0);
  89     pa_assert(!thread);
  90     pa_assert(pipe_fd[0] < 0);
  91     pa_assert(pipe_fd[1] < 0);
  92
  93     if (pa_pipe_cloexec(pipe_fd) < 0)
  94         return -1;
  95
  96     pa_make_fd_nonblock(pipe_fd[1]);
  97     pa_make_fd_nonblock(pipe_fd[0]);
  98
  99     lock_fd_mutex = pa_mutex_new(false, false);
 100
 101     n_ref = 1;
 102     return 0;
 103 }
 104
 105 static void unref(bool after_fork) {
 106
 107     pa_assert(n_ref > 0);
 108     pa_assert(pipe_fd[0] >= 0);
 109     pa_assert(pipe_fd[1] >= 0);
 110     pa_assert(lock_fd_mutex);
 111
 112     n_ref--;
 113
 114     if (n_ref > 0)
 115         return;
 116
 117     /* Join threads only in the process the new thread was created in
 118      * to avoid undefined behaviour.
 119      * POSIX.1-2008 XSH 2.9.2 Thread IDs: "applications should only assume
 120      * that thread IDs are usable and unique within a single process." */
 121     if (thread) {
 122         if (after_fork)
 123             pa_thread_free_nojoin(thread);
 124         else
 125             pa_thread_free(thread);
 126         thread = NULL;
 127     }
 128
 129     pa_mutex_lock(lock_fd_mutex);
 130
 131     pa_assert(state != STATE_TAKEN);
 132
 133     if (state == STATE_OWNING) {
 134
 135         pa_assert(lock_fd >= 0);
 136
 137         if (after_fork)
 138             pa_close(lock_fd);
 139         else {
 140             char *lf;
 141
 142             if (!(lf = pa_runtime_path(AUTOSPAWN_LOCK)))
 143                 pa_log_warn(_("Cannot access autospawn lock."));
 144
 145             pa_unlock_lockfile(lf, lock_fd);
 146             pa_xfree(lf);
 147         }
 148     }
 149
 150     lock_fd = -1;
 151     state = STATE_IDLE;
 152
 153     pa_mutex_unlock(lock_fd_mutex);
 154
 155     pa_mutex_free(lock_fd_mutex);
 156     lock_fd_mutex = NULL;
 157
 158     pa_close(pipe_fd[0]);
 159     pa_close(pipe_fd[1]);
 160     pipe_fd[0] = pipe_fd[1] = -1;
 161 }
 162
 163 static void ping(void) {
 164     ssize_t s;
 165
 166     pa_assert(pipe_fd[1] >= 0);
 167
 168     for (;;) {
 169         char x = 'x';
 170
 171         if ((s = pa_write(pipe_fd[1], &x, 1, NULL)) == 1)
 172             break;
 173
 174         pa_assert(s < 0);
 175
 176         if (errno == EAGAIN)
 177             break;
 178
 179         pa_assert(errno == EINTR);
 180     }
 181 }
 182
 183 static void wait_for_ping(void) {
 184     ssize_t s;
 185     char x;
 186     struct pollfd pfd;
 187     int k;
 188
 189     pa_assert(pipe_fd[0] >= 0);
 190
 191     memset(&pfd, 0, sizeof(pfd));
 192     pfd.fd = pipe_fd[0];
 193     pfd.events = POLLIN;
 194
 195     if ((k = pa_poll(&pfd, 1, -1)) != 1) {
 196         pa_assert(k < 0);
 197         pa_assert(errno == EINTR);
 198     } else if ((s = pa_read(pipe_fd[0], &x, 1, NULL)) != 1) {
 199         pa_assert(s < 0);
 200         pa_assert(errno == EAGAIN);
 201     }
 202 }
 203
 204 static void empty_pipe(void) {
 205     char x[16];
 206     ssize_t s;
 207
 208     pa_assert(pipe_fd[0] >= 0);
 209
 210     if ((s = pa_read(pipe_fd[0], &x, sizeof(x), NULL)) < 1) {
 211         pa_assert(s < 0);
 212         pa_assert(errno == EAGAIN);
 213     }
 214 }
 215
 216 static void thread_func(void *u) {
 217     int fd;
 218     char *lf;
 219
 220 #ifdef HAVE_PTHREAD
 221     sigset_t fullset;
 222
 223     /* No signals in this thread please */
 224     sigfillset(&fullset);
 225     pthread_sigmask(SIG_BLOCK, &fullset, NULL);
 226 #endif
 227
 228     if (!(lf = pa_runtime_path(AUTOSPAWN_LOCK))) {
 229         pa_log_warn(_("Cannot access autospawn lock."));
 230         goto fail;
 231     }
 232
 233     if ((fd = pa_lock_lockfile(lf)) < 0)
 234         goto fail;
 235
 236     pa_mutex_lock(lock_fd_mutex);
 237     pa_assert(state == STATE_IDLE);
 238     lock_fd = fd;
 239     state = STATE_OWNING;
 240     pa_mutex_unlock(lock_fd_mutex);
 241
 242     goto finish;
 243
 244 fail:
 245     pa_mutex_lock(lock_fd_mutex);
 246     pa_assert(state == STATE_IDLE);
 247     state = STATE_FAILED;
 248     pa_mutex_unlock(lock_fd_mutex);
 249
 250 finish:
 251     pa_xfree(lf);
 252
 253     ping();
 254 }
 255
 256 static int start_thread(void) {
 257
 258     if (!thread)
 259         if (!(thread = pa_thread_new("autospawn", thread_func, NULL)))
 260             return -1;
 261
 262     return 0;
 263 }
 264
 265 static void create_mutex(void) {
 266     PA_ONCE_BEGIN {
 267         mutex = pa_mutex_new(false, false);
 268     } PA_ONCE_END;
 269 }
 270
 271 static void destroy_mutex(void) {
 272     if (mutex)
 273         pa_mutex_free(mutex);
 274 }
 275
 276 int pa_autospawn_lock_init(void) {
 277     int ret = -1;
 278
 279     create_mutex();
 280     pa_mutex_lock(mutex);
 281
 282     if (ref() < 0)
 283         ret = -1;
 284     else
 285         ret = pipe_fd[0];
 286
 287     pa_mutex_unlock(mutex);
 288
 289     return ret;
 290 }
 291
 292 int pa_autospawn_lock_acquire(bool block) {
 293     int ret = -1;
 294
 295     create_mutex();
 296     pa_mutex_lock(mutex);
 297     pa_assert(n_ref >= 1);
 298
 299     pa_mutex_lock(lock_fd_mutex);
 300
 301     for (;;) {
 302
 303         empty_pipe();
 304
 305         if (state == STATE_OWNING) {
 306             state = STATE_TAKEN;
 307             ret = 1;
 308             break;
 309         }
 310
 311         if (state == STATE_FAILED) {
 312             ret = -1;
 313             break;
 314         }
 315
 316         if (state == STATE_IDLE)
 317             if (start_thread() < 0)
 318                 break;
 319
 320         if (!block) {
 321             ret = 0;
 322             break;
 323         }
 324
 325         pa_mutex_unlock(lock_fd_mutex);
 326         pa_mutex_unlock(mutex);
 327
 328         wait_for_ping();
 329
 330         pa_mutex_lock(mutex);
 331         pa_mutex_lock(lock_fd_mutex);
 332     }
 333
 334     pa_mutex_unlock(lock_fd_mutex);
 335
 336     pa_mutex_unlock(mutex);
 337
 338     return ret;
 339 }
 340
 341 void pa_autospawn_lock_release(void) {
 342
 343     create_mutex();
 344     pa_mutex_lock(mutex);
 345     pa_assert(n_ref >= 1);
 346
 347     pa_assert(state == STATE_TAKEN);
 348     state = STATE_OWNING;
 349
 350     ping();
 351
 352     pa_mutex_unlock(mutex);
 353 }
 354
 355 void pa_autospawn_lock_done(bool after_fork) {
 356
 357     create_mutex();
 358     pa_mutex_lock(mutex);
 359     pa_assert(n_ref >= 1);
 360
 361     unref(after_fork);
 362
 363     pa_mutex_unlock(mutex);
 364 }