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authorLennart Poettering <lennart@poettering.net>2007-07-26 13:14:26 +0000
committerLennart Poettering <lennart@poettering.net>2007-07-26 13:14:26 +0000
commit6ad165c68615bacc10213e99a2dd485b5d1f8ed1 (patch)
tree6688d25e709ca3cda83c4444bc12d5b163b33e0b
parent8836396c77de2bf05914ca4d9aaa6d72d0589ecd (diff)
add abstracted file descriptor based semaphore object that is lock-free in the best cases
git-svn-id: file:///home/lennart/svn/public/pulseaudio/branches/lennart@1537 fefdeb5f-60dc-0310-8127-8f9354f1896f
-rw-r--r--src/pulsecore/fdsem.c189
-rw-r--r--src/pulsecore/fdsem.h49
2 files changed, 238 insertions, 0 deletions
diff --git a/src/pulsecore/fdsem.c b/src/pulsecore/fdsem.c
new file mode 100644
index 00000000..4de531ae
--- /dev/null
+++ b/src/pulsecore/fdsem.c
@@ -0,0 +1,189 @@
+/* $Id$ */
+
+/***
+ This file is part of PulseAudio.
+
+ Copyright 2006 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.
+***/
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <unistd.h>
+#include <errno.h>
+
+#include <pulsecore/atomic.h>
+#include <pulsecore/log.h>
+#include <pulsecore/thread.h>
+#include <pulsecore/macro.h>
+#include <pulsecore/core-util.h>
+#include <pulse/xmalloc.h>
+
+#include "fdsem.h"
+
+struct pa_fdsem {
+ int fds[2];
+ pa_atomic_t waiting;
+ pa_atomic_t signalled;
+ pa_atomic_t in_pipe;
+};
+
+pa_fdsem *pa_fdsem_new(void) {
+ pa_fdsem *f;
+
+ f = pa_xnew(pa_fdsem, 1);
+
+ if (pipe(f->fds) < 0) {
+ pa_xfree(f);
+ return NULL;
+ }
+
+ pa_atomic_store(&f->waiting, 0);
+ pa_atomic_store(&f->signalled, 0);
+ pa_atomic_store(&f->in_pipe, 0);
+
+ return f;
+}
+
+void pa_fdsem_free(pa_fdsem *f) {
+ pa_assert(f);
+
+ pa_assert(pa_atomic_load(&f->waiting) == 0);
+
+ close(f->fds[0]);
+ close(f->fds[1]);
+
+ pa_xfree(f);
+}
+
+static void flush(pa_fdsem *f) {
+ ssize_t r;
+ pa_assert(f);
+
+ if (pa_atomic_load(&f->in_pipe) <= 0)
+ return;
+
+ do {
+ char x[10];
+
+ if ((r = read(f->fds[0], &x, sizeof(x))) <= 0) {
+ pa_assert(r < 0 && errno == EINTR);
+ continue;
+ }
+
+ } while (pa_atomic_sub(&f->in_pipe, r) > r);
+}
+
+void pa_fdsem_post(pa_fdsem *f) {
+ pa_assert(f);
+
+ if (pa_atomic_cmpxchg(&f->signalled, 0, 1)) {
+
+ if (pa_atomic_load(&f->waiting)) {
+ ssize_t r;
+ char x = 'x';
+
+ pa_atomic_inc(&f->in_pipe);
+
+ for (;;) {
+
+ if ((r = write(f->fds[1], &x, 1)) != 1) {
+ pa_assert(r < 0 && errno == EINTR);
+ continue;
+ }
+
+ break;
+ }
+ }
+ }
+}
+
+void pa_fdsem_wait(pa_fdsem *f) {
+ pa_assert(f);
+
+ flush(f);
+
+ if (pa_atomic_cmpxchg(&f->signalled, 1, 0))
+ return;
+
+ pa_atomic_inc(&f->waiting);
+
+ while (!pa_atomic_cmpxchg(&f->signalled, 1, 0)) {
+ char x[10];
+ ssize_t r;
+
+ if ((r = read(f->fds[0], &x, sizeof(x))) <= 0) {
+ pa_assert(r < 0 && errno == EINTR);
+ continue;
+ }
+
+ pa_atomic_sub(&f->in_pipe, r);
+ }
+
+ pa_atomic_dec(&f->waiting);
+}
+
+int pa_fdsem_try(pa_fdsem *f) {
+ pa_assert(f);
+
+ flush(f);
+
+ if (pa_atomic_cmpxchg(&f->signalled, 1, 0))
+ return 1;
+
+ return 0;
+}
+
+
+int pa_fdsem_get(pa_fdsem *f) {
+ pa_assert(f);
+
+ return f->fds[0];
+}
+
+int pa_fdsem_before_poll(pa_fdsem *f) {
+ pa_assert(f);
+
+ flush(f);
+
+ if (pa_atomic_cmpxchg(&f->signalled, 1, 0))
+ return -1;
+
+ pa_atomic_inc(&f->waiting);
+
+ if (pa_atomic_cmpxchg(&f->signalled, 1, 0)) {
+ pa_atomic_dec(&f->waiting);
+ return -1;
+ }
+
+ return 0;
+}
+
+int pa_fdsem_after_poll(pa_fdsem *f) {
+ pa_assert(f);
+
+ pa_atomic_dec(&f->waiting);
+
+ flush(f);
+
+ if (pa_atomic_cmpxchg(&f->signalled, 1, 0))
+ return 1;
+
+ return 0;
+}
diff --git a/src/pulsecore/fdsem.h b/src/pulsecore/fdsem.h
new file mode 100644
index 00000000..f38ef205
--- /dev/null
+++ b/src/pulsecore/fdsem.h
@@ -0,0 +1,49 @@
+#ifndef foopulsefdsemhfoo
+#define foopulsefdsemhfoo
+
+/* $Id$ */
+
+/***
+ This file is part of PulseAudio.
+
+ Copyright 2004-2006 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 <sys/types.h>
+#include <pulse/def.h>
+
+/* A simple, asynchronous semaphore which uses fds for sleeping. In
+ * the best case all functions are lock-free unless sleeping is
+ * required. */
+
+typedef struct pa_fdsem pa_fdsem;
+
+pa_fdsem *pa_fdsem_new(void);
+void pa_fdsem_free(pa_fdsem *f);
+
+void pa_fdsem_post(pa_fdsem *f);
+void pa_fdsem_wait(pa_fdsem *f);
+int pa_fdsem_try(pa_fdsem *f);
+
+int pa_fdsem_get(pa_fdsem *f);
+
+int pa_fdsem_before_poll(pa_fdsem *f);
+int pa_fdsem_after_poll(pa_fdsem *f);
+
+
+#endif