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 <fcntl.h>
  27 #include <errno.h>
  28 #include <string.h>
  29 #include <sys/poll.h>
  30 #include <signal.h>
  31 #include <pthread.h>
  32
  33 #include <pulse/i18n.h>
  34 #include <pulse/xmalloc.h>
  35
  36 #include <pulsecore/mutex.h>
  37 #include <pulsecore/thread.h>
  38 #include <pulsecore/core-util.h>
  39
  40 #include "lock-autospawn.h"
  41
  42 /* So, why do we have this complex code here with threads and pipes
  43  * and stuff? For two reasons: POSIX file locks are per-process, not
  44  * per-file descriptor. That means that two contexts within the same
  45  * process that try to create the autospawn lock might end up assuming
  46  * they both managed to lock the file. And then, POSIX locking
  47  * operations are synchronous. If two contexts run from the same event
  48  * loop it must be made sure that they do not block each other, but
  49  * that the locking operation can happen asynchronously. */
  50
  51 #define AUTOSPAWN_LOCK "autospawn.lock"
  52
  53 static pa_mutex *mutex;
  54
  55 static unsigned n_ref = 0;
  56 static int lock_fd = -1;
  57 static pa_mutex *lock_fd_mutex = NULL;
  58 static pa_thread *thread = NULL;
  59 static int pipe_fd[2] = { -1, -1 };
  60
  61 static enum {
  62     STATE_IDLE,
  63     STATE_OWNING,
  64     STATE_TAKEN,
  65     STATE_FAILED
  66 } state = STATE_IDLE;
  67
  68 static void destroy_mutex(void) PA_GCC_DESTRUCTOR;
  69
  70 static int ref(void) {
  71
  72     if (n_ref > 0) {
  73
  74         pa_assert(pipe_fd[0] >= 0);
  75         pa_assert(pipe_fd[1] >= 0);
  76         pa_assert(lock_fd_mutex);
  77
  78         n_ref++;
  79
  80         return 0;
  81     }
  82
  83     pa_assert(!lock_fd_mutex);
  84     pa_assert(state == STATE_IDLE);
  85     pa_assert(lock_fd < 0);
  86     pa_assert(!thread);
  87     pa_assert(pipe_fd[0] < 0);
  88     pa_assert(pipe_fd[1] < 0);
  89
  90     if (pipe(pipe_fd) < 0)
  91         return -1;
  92
  93     pa_make_fd_cloexec(pipe_fd[0]);
  94     pa_make_fd_cloexec(pipe_fd[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(pa_bool_t 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     if (thread) {
 118         pa_thread_free(thread);
 119         thread = NULL;
 120     }
 121
 122     pa_mutex_lock(lock_fd_mutex);
 123
 124     pa_assert(state != STATE_TAKEN);
 125
 126     if (state == STATE_OWNING) {
 127
 128         pa_assert(lock_fd >= 0);
 129
 130         if (after_fork)
 131             pa_close(lock_fd);
 132         else {
 133             char *lf;
 134
 135             if (!(lf = pa_runtime_path(AUTOSPAWN_LOCK)))
 136                 pa_log_warn(_("Cannot access autospawn lock."));
 137
 138             pa_unlock_lockfile(lf, lock_fd);
 139             pa_xfree(lf);
 140         }
 141     }
 142
 143     lock_fd = -1;
 144     state = STATE_IDLE;
 145
 146     pa_mutex_unlock(lock_fd_mutex);
 147
 148     pa_mutex_free(lock_fd_mutex);
 149     lock_fd_mutex = NULL;
 150
 151     pa_close(pipe_fd[0]);
 152     pa_close(pipe_fd[1]);
 153     pipe_fd[0] = pipe_fd[1] = -1;
 154 }
 155
 156 static void ping(void) {
 157     ssize_t s;
 158
 159     pa_assert(pipe_fd[1] >= 0);
 160
 161     for (;;) {
 162         char x = 'x';
 163
 164         if ((s = write(pipe_fd[1], &x, 1)) == 1)
 165             break;
 166
 167         pa_assert(s < 0);
 168
 169         if (errno == EAGAIN)
 170             break;
 171
 172         pa_assert(errno == EINTR);
 173     }
 174 }
 175
 176 static void wait_for_ping(void) {
 177     ssize_t s;
 178     char x;
 179     struct pollfd pfd;
 180     int k;
 181
 182     pa_assert(pipe_fd[0] >= 0);
 183
 184     memset(&pfd, 0, sizeof(pfd));
 185     pfd.fd = pipe_fd[0];
 186     pfd.events = POLLIN;
 187
 188     if ((k = poll(&pfd, 1, -1)) != 1) {
 189         pa_assert(k < 0);
 190         pa_assert(errno == EINTR);
 191     } else if ((s = read(pipe_fd[0], &x, 1)) != 1) {
 192         pa_assert(s < 0);
 193         pa_assert(errno == EAGAIN);
 194     }
 195 }
 196
 197 static void empty_pipe(void) {
 198     char x[16];
 199     ssize_t s;
 200
 201     pa_assert(pipe_fd[0] >= 0);
 202
 203     if ((s = read(pipe_fd[0], &x, sizeof(x))) < 1) {
 204         pa_assert(s < 0);
 205         pa_assert(errno == EAGAIN);
 206     }
 207 }
 208
 209 static void thread_func(void *u) {
 210     int fd;
 211     char *lf;
 212     sigset_t fullset;
 213
 214     /* No signals in this thread please */
 215     sigfillset(&fullset);
 216     pthread_sigmask(SIG_BLOCK, &fullset, NULL);
 217
 218     if (!(lf = pa_runtime_path(AUTOSPAWN_LOCK))) {
 219         pa_log_warn(_("Cannot access autospawn lock."));
 220         goto fail;
 221     }
 222
 223     if ((fd = pa_lock_lockfile(lf)) < 0)
 224         goto fail;
 225
 226     pa_mutex_lock(lock_fd_mutex);
 227     pa_assert(state == STATE_IDLE);
 228     lock_fd = fd;
 229     state = STATE_OWNING;
 230     pa_mutex_unlock(lock_fd_mutex);
 231
 232     goto finish;
 233
 234 fail:
 235     pa_mutex_lock(lock_fd_mutex);
 236     pa_assert(state == STATE_IDLE);
 237     state = STATE_FAILED;
 238     pa_mutex_unlock(lock_fd_mutex);
 239
 240 finish:
 241     pa_xfree(lf);
 242
 243     ping();
 244 }
 245
 246 static int start_thread(void) {
 247
 248     if (!thread)
 249         if (!(thread = pa_thread_new(thread_func, NULL)))
 250             return -1;
 251
 252     return 0;
 253 }
 254
 255 static void create_mutex(void) {
 256     PA_ONCE_BEGIN {
 257         mutex = pa_mutex_new(FALSE, FALSE);
 258     } PA_ONCE_END;
 259 }
 260
 261 static void destroy_mutex(void) {
 262     if (mutex)
 263         pa_mutex_free(mutex);
 264 }
 265
 266 int pa_autospawn_lock_init(void) {
 267     int ret = -1;
 268
 269     create_mutex();
 270     pa_mutex_lock(mutex);
 271
 272     if (ref() < 0)
 273         ret = -1;
 274     else
 275         ret = pipe_fd[0];
 276
 277     pa_mutex_unlock(mutex);
 278
 279     return ret;
 280 }
 281
 282 int pa_autospawn_lock_acquire(pa_bool_t block) {
 283     int ret = -1;
 284
 285     create_mutex();
 286     pa_mutex_lock(mutex);
 287     pa_assert(n_ref >= 1);
 288
 289     pa_mutex_lock(lock_fd_mutex);
 290
 291     for (;;) {
 292
 293         empty_pipe();
 294
 295         if (state == STATE_OWNING) {
 296             state = STATE_TAKEN;
 297             ret = 1;
 298             break;
 299         }
 300
 301         if (state == STATE_FAILED) {
 302             ret = -1;
 303             break;
 304         }
 305
 306         if (state == STATE_IDLE)
 307             if (start_thread() < 0)
 308                 break;
 309
 310         if (!block) {
 311             ret = 0;
 312             break;
 313         }
 314
 315         pa_mutex_unlock(lock_fd_mutex);
 316         pa_mutex_unlock(mutex);
 317
 318         wait_for_ping();
 319
 320         pa_mutex_lock(mutex);
 321         pa_mutex_lock(lock_fd_mutex);
 322     }
 323
 324     pa_mutex_unlock(lock_fd_mutex);
 325
 326     pa_mutex_unlock(mutex);
 327
 328     return ret;
 329 }
 330
 331 void pa_autospawn_lock_release(void) {
 332
 333     create_mutex();
 334     pa_mutex_lock(mutex);
 335     pa_assert(n_ref >= 1);
 336
 337     pa_assert(state == STATE_TAKEN);
 338     state = STATE_OWNING;
 339
 340     ping();
 341
 342     pa_mutex_unlock(mutex);
 343 }
 344
 345 void pa_autospawn_lock_done(pa_bool_t after_fork) {
 346
 347     create_mutex();
 348     pa_mutex_lock(mutex);
 349     pa_assert(n_ref >= 1);
 350
 351     unref(after_fork);
 352
 353     pa_mutex_unlock(mutex);
 354 }