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/i18n.h>
  36 #include <pulse/xmalloc.h>
  37
  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(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 = pa_write(pipe_fd[1], &x, 1, NULL)) == 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 = pa_poll(&pfd, 1, -1)) != 1) {
 189         pa_assert(k < 0);
 190         pa_assert(errno == EINTR);
 191     } else if ((s = pa_read(pipe_fd[0], &x, 1, NULL)) != 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 = pa_read(pipe_fd[0], &x, sizeof(x), NULL)) < 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
 213 #ifdef HAVE_PTHREAD
 214     sigset_t fullset;
 215
 216     /* No signals in this thread please */
 217     sigfillset(&fullset);
 218     pthread_sigmask(SIG_BLOCK, &fullset, NULL);
 219 #endif
 220
 221     if (!(lf = pa_runtime_path(AUTOSPAWN_LOCK))) {
 222         pa_log_warn(_("Cannot access autospawn lock."));
 223         goto fail;
 224     }
 225
 226     if ((fd = pa_lock_lockfile(lf)) < 0)
 227         goto fail;
 228
 229     pa_mutex_lock(lock_fd_mutex);
 230     pa_assert(state == STATE_IDLE);
 231     lock_fd = fd;
 232     state = STATE_OWNING;
 233     pa_mutex_unlock(lock_fd_mutex);
 234
 235     goto finish;
 236
 237 fail:
 238     pa_mutex_lock(lock_fd_mutex);
 239     pa_assert(state == STATE_IDLE);
 240     state = STATE_FAILED;
 241     pa_mutex_unlock(lock_fd_mutex);
 242
 243 finish:
 244     pa_xfree(lf);
 245
 246     ping();
 247 }
 248
 249 static int start_thread(void) {
 250
 251     if (!thread)
 252         if (!(thread = pa_thread_new("autospawn", thread_func, NULL)))
 253             return -1;
 254
 255     return 0;
 256 }
 257
 258 static void create_mutex(void) {
 259     PA_ONCE_BEGIN {
 260         mutex = pa_mutex_new(FALSE, FALSE);
 261     } PA_ONCE_END;
 262 }
 263
 264 static void destroy_mutex(void) {
 265     if (mutex)
 266         pa_mutex_free(mutex);
 267 }
 268
 269 int pa_autospawn_lock_init(void) {
 270     int ret = -1;
 271
 272     create_mutex();
 273     pa_mutex_lock(mutex);
 274
 275     if (ref() < 0)
 276         ret = -1;
 277     else
 278         ret = pipe_fd[0];
 279
 280     pa_mutex_unlock(mutex);
 281
 282     return ret;
 283 }
 284
 285 int pa_autospawn_lock_acquire(pa_bool_t block) {
 286     int ret = -1;
 287
 288     create_mutex();
 289     pa_mutex_lock(mutex);
 290     pa_assert(n_ref >= 1);
 291
 292     pa_mutex_lock(lock_fd_mutex);
 293
 294     for (;;) {
 295
 296         empty_pipe();
 297
 298         if (state == STATE_OWNING) {
 299             state = STATE_TAKEN;
 300             ret = 1;
 301             break;
 302         }
 303
 304         if (state == STATE_FAILED) {
 305             ret = -1;
 306             break;
 307         }
 308
 309         if (state == STATE_IDLE)
 310             if (start_thread() < 0)
 311                 break;
 312
 313         if (!block) {
 314             ret = 0;
 315             break;
 316         }
 317
 318         pa_mutex_unlock(lock_fd_mutex);
 319         pa_mutex_unlock(mutex);
 320
 321         wait_for_ping();
 322
 323         pa_mutex_lock(mutex);
 324         pa_mutex_lock(lock_fd_mutex);
 325     }
 326
 327     pa_mutex_unlock(lock_fd_mutex);
 328
 329     pa_mutex_unlock(mutex);
 330
 331     return ret;
 332 }
 333
 334 void pa_autospawn_lock_release(void) {
 335
 336     create_mutex();
 337     pa_mutex_lock(mutex);
 338     pa_assert(n_ref >= 1);
 339
 340     pa_assert(state == STATE_TAKEN);
 341     state = STATE_OWNING;
 342
 343     ping();
 344
 345     pa_mutex_unlock(mutex);
 346 }
 347
 348 void pa_autospawn_lock_done(pa_bool_t after_fork) {
 349
 350     create_mutex();
 351     pa_mutex_lock(mutex);
 352     pa_assert(n_ref >= 1);
 353
 354     unref(after_fork);
 355
 356     pa_mutex_unlock(mutex);
 357 }