rework autospawning code to survive multiple pa_contexts in a single process

8 files changed, 595 insertions, 38 deletions

diff --git a/src/.gitignore b/src/.gitignore
index 6902eb9f7..543f4e8ec 100644
--- a/src/.gitignore
+++ b/src/.gitignore
@@ -1,3 +1,4 @@
+lock-autospawn-test
 *.lo
 *.o
 *.la
diff --git a/src/Makefile.am b/src/Makefile.am
index 29a6ef472..21584ad96 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -262,7 +262,8 @@ noinst_PROGRAMS = \
 		envelope-test \
 		proplist-test \
 		rtstutter \
-		stripnul
+		stripnul \
+		lock-autospawn-test
 
 if HAVE_SIGXCPU
 noinst_PROGRAMS += \
@@ -452,6 +453,11 @@ stripnul_LDADD = $(AM_LDADD) libpulsecore.la
 stripnul_CFLAGS = $(AM_CFLAGS) $(LIBOIL_CFLAGS)
 stripnul_LDFLAGS = $(AM_LDFLAGS) $(BINLDFLAGS) $(LIBOIL_LIBS)
 
+lock_autospawn_test_SOURCES = tests/lock-autospawn-test.c
+lock_autospawn_test_LDADD = $(AM_LDADD) libpulsecore.la
+lock_autospawn_test_CFLAGS = $(AM_CFLAGS) $(LIBOIL_CFLAGS)
+lock_autospawn_test_LDFLAGS = $(AM_LDFLAGS) $(BINLDFLAGS) $(LIBOIL_LIBS)
+
 ###################################
 #         Client library          #
 ###################################
@@ -535,7 +541,8 @@ libpulse_la_SOURCES = \
 		pulse/xmalloc.c pulse/xmalloc.h \
 		pulse/proplist.c pulse/proplist.h \
 		pulse/ext-stream-restore.c pulse/ext-stream-restore.h \
-		pulse/i18n.c pulse/i18n.h
+		pulse/i18n.c pulse/i18n.h \
+		pulse/lock-autospawn.c pulse/lock-autospawn.h
 
 # Internal stuff that is shared with libpulsecore
 libpulse_la_SOURCES += \
@@ -731,7 +738,8 @@ libpulsecore_la_SOURCES = \
 		pulse/volume.c pulse/volume.h \
 		pulse/xmalloc.c pulse/xmalloc.h \
 		pulse/proplist.c pulse/proplist.h \
-		pulse/i18n.c pulse/i18n.h
+		pulse/i18n.c pulse/i18n.h \
+		pulse/lock-autospawn.c pulse/lock-autospawn.h
 
 # Pure core stuff (some are shared in libpulse though).
 libpulsecore_la_SOURCES += \
diff --git a/src/daemon/main.c b/src/daemon/main.c
index 9cdcb6cd7..c6fb3c69c 100644
--- a/src/daemon/main.c
+++ b/src/daemon/main.c
@@ -65,6 +65,7 @@
 #include <pulse/timeval.h>
 #include <pulse/xmalloc.h>
 #include <pulse/i18n.h>
+#include <pulse/lock-autospawn.h>
 
 #include <pulsecore/winsock.h>
 #include <pulsecore/core-error.h>
@@ -95,8 +96,6 @@
 #include "ltdl-bind-now.h"
 #include "polkit.h"
 
-#define AUTOSPAWN_LOCK "autospawn.lock"
-
 #ifdef HAVE_LIBWRAP
 /* Only one instance of these variables */
 int allow_severity = LOG_INFO;
@@ -346,7 +345,8 @@ int main(int argc, char *argv[]) {
     struct timeval win32_tv;
 #endif
     char *lf = NULL;
-    int autospawn_lock_fd = -1;
+    int autospawn_fd = -1;
+    pa_bool_t autospawn_locked = FALSE;
 
 #if defined(__linux__) && defined(__OPTIMIZE__)
     /*
@@ -656,8 +656,17 @@ int main(int argc, char *argv[]) {
          * first take the autospawn lock to make things
          * synchronous. */
 
-        lf = pa_runtime_path(AUTOSPAWN_LOCK);
-        autospawn_lock_fd = pa_lock_lockfile(lf);
+        if ((autospawn_fd = pa_autospawn_lock_init()) < 0) {
+            pa_log("Failed to initialize autospawn lock");
+            goto finish;
+        }
+
+        if ((pa_autospawn_lock_acquire(TRUE) < 0)) {
+            pa_log("Failed to acquire autospawn lock");
+            goto finish;
+        }
+
+        autospawn_locked = TRUE;
     }
 
     if (conf->daemonize) {
@@ -703,12 +712,15 @@ int main(int argc, char *argv[]) {
             goto finish;
         }
 
-        if (autospawn_lock_fd >= 0) {
+        if (autospawn_fd >= 0) {
             /* The lock file is unlocked from the parent, so we need
              * to close it in the child */
 
-            pa_close(autospawn_lock_fd);
-            autospawn_lock_fd = -1;
+            pa_autospawn_lock_release();
+            pa_autospawn_lock_done(TRUE);
+
+            autospawn_locked = FALSE;
+            autospawn_fd = -1;
         }
 
         pa_assert_se(pa_close(daemon_pipe[0]) == 0);
@@ -917,8 +929,12 @@ int main(int argc, char *argv[]) {
 
 finish:
 
-    if (autospawn_lock_fd >= 0)
-        pa_unlock_lockfile(lf, autospawn_lock_fd);
+    if (autospawn_fd >= 0) {
+        if (autospawn_locked)
+            pa_autospawn_lock_release();
+
+        pa_autospawn_lock_done(FALSE);
+    }
 
     if (lf)
         pa_xfree(lf);
diff --git a/src/pulse/context.c b/src/pulse/context.c
index bdd519a65..00236b964 100644
--- a/src/pulse/context.c
+++ b/src/pulse/context.c
@@ -54,6 +54,7 @@
 #include <pulse/utf8.h>
 #include <pulse/util.h>
 #include <pulse/i18n.h>
+#include <pulse/lock-autospawn.h>
 
 #include <pulsecore/winsock.h>
 #include <pulsecore/core-error.h>
@@ -81,8 +82,6 @@
 
 #include "context.h"
 
-#define AUTOSPAWN_LOCK "autospawn.lock"
-
 void pa_command_extension(pa_pdispatch *pd, uint32_t command, uint32_t tag, pa_tagstruct *t, void *userdata);
 
 static const pa_pdispatch_cb_t command_table[PA_COMMAND_MAX] = {
@@ -100,20 +99,23 @@ static const pa_pdispatch_cb_t command_table[PA_COMMAND_MAX] = {
     [PA_COMMAND_EXTENSION] = pa_command_extension
 };
 
-static void unlock_autospawn_lock_file(pa_context *c) {
+static void unlock_autospawn(pa_context *c) {
     pa_assert(c);
 
-    if (c->autospawn_lock_fd >= 0) {
-        char *lf;
+    if (c->autospawn_fd >= 0) {
 
-        if (!(lf = pa_runtime_path(AUTOSPAWN_LOCK)))
-            pa_log_warn(_("Cannot unlock autospawn because runtime path is no more."));
+        if (c->autospawn_locked)
+            pa_autospawn_lock_release();
 
-        pa_unlock_lockfile(lf, c->autospawn_lock_fd);
-        pa_xfree(lf);
+        if (c->autospawn_event)
+            c->mainloop->io_free(c->autospawn_event);
 
-        c->autospawn_lock_fd = -1;
+        pa_autospawn_lock_done(FALSE);
     }
+
+    c->autospawn_locked = FALSE;
+    c->autospawn_fd = -1;
+    c->autospawn_event = NULL;
 }
 
 static void context_free(pa_context *c);
@@ -174,11 +176,15 @@ pa_context *pa_context_new_with_proplist(pa_mainloop_api *mainloop, const char *
     c->is_local = FALSE;
     c->server_list = NULL;
     c->server = NULL;
-    c->autospawn_lock_fd = -1;
-    memset(&c->spawn_api, 0, sizeof(c->spawn_api));
-    c->do_autospawn = FALSE;
+
     c->do_shm = FALSE;
 
+    c->do_autospawn = FALSE;
+    c->autospawn_fd = -1;
+    c->autospawn_locked = FALSE;
+    c->autospawn_event = NULL;
+    memset(&c->spawn_api, 0, sizeof(c->spawn_api));
+
 #ifndef MSG_NOSIGNAL
 #ifdef SIGPIPE
     pa_check_signal_is_blocked(SIGPIPE);
@@ -246,7 +252,7 @@ static void context_free(pa_context *c) {
 
     context_unlink(c);
 
-    unlock_autospawn_lock_file(c);
+    unlock_autospawn(c);
 
     if (c->record_streams)
         pa_dynarray_free(c->record_streams, NULL, NULL);
@@ -674,7 +680,7 @@ static int context_connect_spawn(pa_context *c) {
 
     c->is_local = TRUE;
 
-    unlock_autospawn_lock_file(c);
+    unlock_autospawn(c);
 
     io = pa_iochannel_new(c->mainloop, fds[0], fds[0]);
     setup_context(c, io);
@@ -686,7 +692,7 @@ static int context_connect_spawn(pa_context *c) {
 fail:
     pa_close_pipe(fds);
 
-    unlock_autospawn_lock_file(c);
+    unlock_autospawn(c);
 
     pa_context_unref(c);
 
@@ -768,13 +774,46 @@ static void on_connection(pa_socket_client *client, pa_iochannel*io, void *userd
         goto finish;
     }
 
-    unlock_autospawn_lock_file(c);
+    unlock_autospawn(c);
     setup_context(c, io);
 
 finish:
     pa_context_unref(c);
 }
 
+static void autospawn_cb(pa_mainloop_api*a, pa_io_event *e, int fd, pa_io_event_flags_t events, void *userdata) {
+    pa_context *c = userdata;
+    int k;
+
+    pa_assert(a);
+    pa_assert(e);
+    pa_assert(fd >= 0);
+    pa_assert(events = PA_IO_EVENT_INPUT);
+    pa_assert(c);
+    pa_assert(e == c->autospawn_event);
+    pa_assert(fd == c->autospawn_fd);
+
+    pa_context_ref(c);
+
+    /* Check whether we can get the lock right now*/
+    if ((k = pa_autospawn_lock_acquire(FALSE)) < 0) {
+        pa_context_fail(c, PA_ERR_ACCESS);
+        goto finish;
+    }
+
+    if (k > 0) {
+        /* So we got it, rock on! */
+        c->autospawn_locked = TRUE;
+        try_next_connection(c);
+
+        c->mainloop->io_free(c->autospawn_event);
+        c->autospawn_event = NULL;
+    }
+
+finish:
+
+    pa_context_unref(c);
+}
 
 static char *get_old_legacy_runtime_dir(void) {
     char *p, u[128];
@@ -847,6 +886,7 @@ int pa_context_connect(
             pa_context_fail(c, PA_ERR_INVALIDSERVER);
             goto finish;
         }
+
     } else {
         char *d, *ufn;
         static char *legacy_dir;
@@ -895,21 +935,40 @@ int pa_context_connect(
 
         /* Wrap the connection attempts in a single transaction for sane autospawn locking */
         if (!(flags & PA_CONTEXT_NOAUTOSPAWN) && c->conf->autospawn) {
-            char *lf;
+            int k;
 
-            if (!(lf = pa_runtime_path(AUTOSPAWN_LOCK))) {
+            pa_assert(c->autospawn_fd < 0);
+            pa_assert(!c->autospawn_locked);
+
+            /* Start the locking procedure */
+            if ((c->autospawn_fd = pa_autospawn_lock_init()) < 0) {
                 pa_context_fail(c, PA_ERR_ACCESS);
                 goto finish;
             }
 
-            pa_assert(c->autospawn_lock_fd <= 0);
-            c->autospawn_lock_fd = pa_lock_lockfile(lf);
-            pa_xfree(lf);
-
             if (api)
                 c->spawn_api = *api;
 
             c->do_autospawn = TRUE;
+
+            /* Check whether we can get the lock right now*/
+            if ((k = pa_autospawn_lock_acquire(FALSE)) < 0) {
+                pa_context_fail(c, PA_ERR_ACCESS);
+                goto finish;
+            }
+
+            if (k > 0)
+                /* So we got it, rock on! */
+                c->autospawn_locked = TRUE;
+            else {
+                /* Hmm, we didn't get it, so let's wait for it */
+                c->autospawn_event = c->mainloop->io_new(c->mainloop, c->autospawn_fd, PA_IO_EVENT_INPUT, autospawn_cb, c);
+
+                pa_context_set_state(c, PA_CONTEXT_CONNECTING);
+                r = 0;
+                goto finish;
+            }
+
         }
     }
 
diff --git a/src/pulse/internal.h b/src/pulse/internal.h
index bfe888eeb..26fb04d4d 100644
--- a/src/pulse/internal.h
+++ b/src/pulse/internal.h
@@ -75,9 +75,12 @@ struct pa_context {
     pa_mempool *mempool;
 
     pa_bool_t is_local:1;
-    pa_bool_t do_autospawn:1;
     pa_bool_t do_shm:1;
-    int autospawn_lock_fd;
+
+    pa_bool_t do_autospawn:1;
+    pa_bool_t autospawn_locked:1;
+    int autospawn_fd;
+    pa_io_event *autospawn_event;
     pa_spawn_api spawn_api;
 
     pa_strlist *server_list;
diff --git a/src/pulse/lock-autospawn.c b/src/pulse/lock-autospawn.c
new file mode 100644
index 000000000..33a531138
--- /dev/null
+++ b/src/pulse/lock-autospawn.c
@@ -0,0 +1,329 @@
+/***
+  This file is part of PulseAudio.
+
+  Copyright 2008 Lennart Poettering
+
+  PulseAudio is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License as published
+  by the Free Software Foundation; either version 2 of the License,
+  or (at your option) any later version.
+
+  PulseAudio is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with PulseAudio; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+  USA.
+***/
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <fcntl.h>
+#include <errno.h>
+#include <string.h>
+#include <sys/poll.h>
+#include <signal.h>
+#include <pthread.h>
+
+#include <pulse/i18n.h>
+#include <pulse/xmalloc.h>
+
+#include <pulsecore/mutex.h>
+#include <pulsecore/thread.h>
+#include <pulsecore/core-util.h>
+
+#include "lock-autospawn.h"
+
+/* So, why do we have this complex code here with threads and pipes
+ * and stuff? For two reasons: POSIX file locks are per-process, not
+ * per-file descriptor. That means that two contexts within the same
+ * process that try to create the autospawn lock might end up assuming
+ * they both managed to lock the file. And then, POSIX locking
+ * operations are synchronous. If two contexts run from the same event
+ * loop it must be made sure that they do not block each other, but
+ * that the locking operation can happen asynchronously. */
+
+#define AUTOSPAWN_LOCK "autospawn.lock"
+
+static pa_mutex *mutex;
+
+static unsigned n_ref = 0;
+static int lock_fd = -1;
+static pa_mutex *lock_fd_mutex = NULL;
+static pa_bool_t taken = FALSE;
+static pa_thread *thread;
+static int pipe_fd[2] = { -1, -1 };
+
+static void destroy_mutex(void) PA_GCC_DESTRUCTOR;
+
+static int ref(void) {
+
+    if (n_ref > 0) {
+
+        pa_assert(pipe_fd[0] >= 0);
+        pa_assert(pipe_fd[1] >= 0);
+
+        n_ref++;
+
+        return 0;
+    }
+
+    pa_assert(lock_fd < 0);
+    pa_assert(!lock_fd_mutex);
+    pa_assert(!taken);
+    pa_assert(!thread);
+    pa_assert(pipe_fd[0] < 0);
+    pa_assert(pipe_fd[1] < 0);
+
+    if (pipe(pipe_fd) < 0)
+        return -1;
+
+    lock_fd_mutex = pa_mutex_new(FALSE, FALSE);
+
+    pa_make_fd_cloexec(pipe_fd[0]);
+    pa_make_fd_cloexec(pipe_fd[1]);
+
+    pa_make_fd_nonblock(pipe_fd[1]);
+    pa_make_fd_nonblock(pipe_fd[0]);
+
+    n_ref = 1;
+    return 0;
+}
+
+static void unref(pa_bool_t after_fork) {
+
+    pa_assert(n_ref > 0);
+    pa_assert(pipe_fd[0] >= 0);
+    pa_assert(pipe_fd[1] >= 0);
+    pa_assert(lock_fd_mutex);
+
+    n_ref--;
+
+    if (n_ref > 0)
+        return;
+
+    pa_assert(!taken);
+
+    if (thread) {
+        pa_thread_free(thread);
+        thread = NULL;
+    }
+
+    pa_mutex_lock(lock_fd_mutex);
+    if (lock_fd >= 0) {
+
+        if (after_fork)
+            pa_close(lock_fd);
+        else {
+            char *lf;
+
+            if (!(lf = pa_runtime_path(AUTOSPAWN_LOCK)))
+                pa_log_warn(_("Cannot access autospawn lock."));
+
+            pa_unlock_lockfile(lf, lock_fd);
+            pa_xfree(lf);
+
+            lock_fd = -1;
+        }
+    }
+    pa_mutex_unlock(lock_fd_mutex);
+
+    pa_mutex_free(lock_fd_mutex);
+
+    pa_close(pipe_fd[0]);
+    pa_close(pipe_fd[1]);
+    pipe_fd[0] = pipe_fd[1] = -1;
+}
+
+static void ping(void) {
+    ssize_t s;
+
+    pa_assert(pipe_fd[1] >= 0);
+
+    for (;;) {
+        char x = 'x';
+
+        if ((s = write(pipe_fd[1], &x, 1)) == 1)
+            break;
+
+        pa_assert(s < 0);
+
+        if (errno == EAGAIN)
+            break;
+
+        pa_assert(errno == EINTR);
+    }
+}
+
+static void wait_for_ping(void) {
+    ssize_t s;
+    char x;
+    struct pollfd pfd;
+    int k;
+
+    pa_assert(pipe_fd[0] >= 0);
+
+    memset(&pfd, 0, sizeof(pfd));
+    pfd.fd = pipe_fd[0];
+    pfd.events = POLLIN;
+
+    if ((k = poll(&pfd, 1, -1)) != 1) {
+        pa_assert(k < 0);
+        pa_assert(errno == EINTR);
+    } else if ((s = read(pipe_fd[0], &x, 1)) != 1) {
+        pa_assert(s < 0);
+        pa_assert(errno == EAGAIN);
+    }
+}
+
+static void empty_pipe(void) {
+    char x[16];
+    ssize_t s;
+
+    pa_assert(pipe_fd[0] >= 0);
+
+    if ((s = read(pipe_fd[0], &x, sizeof(x))) < 1) {
+        pa_assert(s < 0);
+        pa_assert(errno == EAGAIN);
+    }
+}
+
+static void thread_func(void *u) {
+    int fd;
+    char *lf;
+    sigset_t fullset;
+
+    /* No signals in this thread please */
+    sigfillset(&fullset);
+    pthread_sigmask(SIG_BLOCK, &fullset, NULL);
+
+    if (!(lf = pa_runtime_path(AUTOSPAWN_LOCK))) {
+        pa_log_warn(_("Cannot access autospawn lock."));
+        goto finish;
+    }
+
+    if ((fd = pa_lock_lockfile(lf)) < 0)
+        goto finish;
+
+    pa_mutex_lock(lock_fd_mutex);
+    pa_assert(lock_fd < 0);
+    lock_fd = fd;
+    pa_mutex_unlock(lock_fd_mutex);
+
+finish:
+    pa_xfree(lf);
+
+    ping();
+}
+
+static int start_thread(void) {
+
+    if (!thread)
+        if (!(thread = pa_thread_new(thread_func, NULL)))
+            return -1;
+
+    return 0;
+}
+
+static void create_mutex(void) {
+    PA_ONCE_BEGIN {
+        mutex = pa_mutex_new(FALSE, FALSE);
+    } PA_ONCE_END;
+}
+
+static void destroy_mutex(void) {
+
+    if (mutex)
+        pa_mutex_free(mutex);
+}
+
+
+int pa_autospawn_lock_init(void) {
+    int ret = -1;
+
+    create_mutex();
+    pa_mutex_lock(mutex);
+
+    if (ref() < 0)
+        ret = -1;
+    else
+        ret = pipe_fd[0];
+
+    pa_mutex_unlock(mutex);
+
+    return ret;
+}
+
+int pa_autospawn_lock_acquire(pa_bool_t block) {
+    int ret = -1;
+
+    create_mutex();
+    pa_mutex_lock(mutex);
+    pa_assert(n_ref >= 1);
+
+    pa_mutex_lock(lock_fd_mutex);
+
+    for (;;) {
+
+        empty_pipe();
+
+        if (lock_fd >= 0 && !taken) {
+            taken = TRUE;
+            ret = 1;
+            break;
+        }
+
+        if (lock_fd < 0)
+            if (start_thread() < 0)
+                break;
+
+        if (!block) {
+            ret = 0;
+            break;
+        }
+
+        pa_mutex_unlock(lock_fd_mutex);
+        pa_mutex_unlock(mutex);
+
+        wait_for_ping();
+
+        pa_mutex_lock(mutex);
+        pa_mutex_lock(lock_fd_mutex);
+    }
+
+    pa_mutex_unlock(lock_fd_mutex);
+
+    pa_mutex_unlock(mutex);
+
+    return ret;
+}
+
+void pa_autospawn_lock_release(void) {
+
+    create_mutex();
+    pa_mutex_lock(mutex);
+    pa_assert(n_ref >= 1);
+
+    pa_assert(taken);
+    taken = FALSE;
+
+    ping();
+
+    pa_mutex_unlock(mutex);
+}
+
+void pa_autospawn_lock_done(pa_bool_t after_fork) {
+
+    create_mutex();
+    pa_mutex_lock(mutex);
+    pa_assert(n_ref >= 1);
+
+    unref(after_fork);
+
+    pa_mutex_unlock(mutex);
+}
diff --git a/src/pulse/lock-autospawn.h b/src/pulse/lock-autospawn.h
new file mode 100644
index 000000000..c04c4bd17
--- /dev/null
+++ b/src/pulse/lock-autospawn.h
@@ -0,0 +1,32 @@
+#ifndef foopulselockautospawnhfoo
+#define foopulselockautospawnhfoo
+
+/***
+  This file is part of PulseAudio.
+
+  Copyright 2008 Lennart Poettering
+
+  PulseAudio is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License as
+  published by the Free Software Foundation; either version 2.1 of the
+  License, or (at your option) any later version.
+
+  PulseAudio is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with PulseAudio; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+  USA.
+***/
+
+#include <pulsecore/macro.h>
+
+int pa_autospawn_lock_init(void);
+int pa_autospawn_lock_acquire(pa_bool_t block);
+void pa_autospawn_lock_release(void);
+void pa_autospawn_lock_done(pa_bool_t after_fork);
+
+#endif
diff --git a/src/tests/lock-autospawn-test.c b/src/tests/lock-autospawn-test.c
new file mode 100644
index 000000000..cb3dc87c8
--- /dev/null
+++ b/src/tests/lock-autospawn-test.c
@@ -0,0 +1,109 @@
+/***
+  This file is part of PulseAudio.
+
+  Copyright 2008 Lennart Poettering
+
+  PulseAudio is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License as published
+  by the Free Software Foundation; either version 2 of the License,
+  or (at your option) any later version.
+
+  PulseAudio is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with PulseAudio; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+  USA.
+***/
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <sys/poll.h>
+#include <string.h>
+
+#include <pulsecore/macro.h>
+#include <pulsecore/thread.h>
+#include <pulse/lock-autospawn.h>
+#include <pulse/util.h>
+
+static void thread_func(void*k) {
+    pa_assert_se(pa_autospawn_lock_init() >= 0);
+
+    pa_log("%i, Trying to acquire lock.", PA_PTR_TO_INT(k));
+
+    pa_assert_se(pa_autospawn_lock_acquire(TRUE) > 0);
+
+    pa_log("%i, Got the lock!, Sleeping for 5s", PA_PTR_TO_INT(k));
+
+    pa_msleep(5000);
+
+    pa_log("%i, Releasing", PA_PTR_TO_INT(k));
+
+    pa_autospawn_lock_release();
+
+    pa_autospawn_lock_done(FALSE);
+}
+
+static void thread_func2(void *k) {
+    int fd;
+
+    pa_assert_se((fd = pa_autospawn_lock_init()) >= 0);
+
+    pa_log("%i, Trying to acquire lock.", PA_PTR_TO_INT(k));
+
+    for (;;) {
+        struct pollfd pollfd;
+        int j;
+
+        if ((j = pa_autospawn_lock_acquire(FALSE)) > 0)
+            break;
+
+        pa_assert(j == 0);
+
+        memset(&pollfd, 0, sizeof(pollfd));
+        pollfd.fd = fd;
+        pollfd.events = POLLIN;
+
+        pa_assert_se(poll(&pollfd, 1, -1) == 1);
+
+        pa_log("%i, woke up", PA_PTR_TO_INT(k));
+    }
+
+    pa_log("%i, Got the lock!, Sleeping for 5s", PA_PTR_TO_INT(k));
+
+    pa_msleep(5000);
+
+    pa_log("%i, Releasing", PA_PTR_TO_INT(k));
+
+    pa_autospawn_lock_release();
+
+    pa_autospawn_lock_done(FALSE);
+}
+
+int main(int argc, char**argv) {
+    pa_thread *a, *b, *c, *d;
+
+    pa_assert_se((a = pa_thread_new(thread_func, PA_INT_TO_PTR(1))));
+    pa_assert_se((b = pa_thread_new(thread_func2, PA_INT_TO_PTR(2))));
+    pa_assert_se((c = pa_thread_new(thread_func2, PA_INT_TO_PTR(3))));
+    pa_assert_se((d = pa_thread_new(thread_func, PA_INT_TO_PTR(4))));
+
+    pa_thread_join(a);
+    pa_thread_join(b);
+    pa_thread_join(c);
+    pa_thread_join(d);
+
+    pa_thread_free(a);
+    pa_thread_free(b);
+    pa_thread_free(c);
+    pa_thread_free(d);
+
+    pa_log("End");
+
+    return 0;
+}