lavu: add support for atomic operations.

These could be used for reference counting, or for keeping track of
decoding progress in references in multithreaded decoders.

Support is provided by gcc/msvc/suncc intrinsics, with a fallback using
pthread mutexes.

Signed-off-by: Anton Khirnov <anton@khirnov.net>

1 files changed, 123 insertions, 0 deletions

diff --git a/libavutil/atomic.c b/libavutil/atomic.c
new file mode 100644
index 0000000000..8fa2532fd6
--- /dev/null
+++ b/libavutil/atomic.c
@@ -0,0 +1,123 @@
+/*
+ * Copyright (c) 2012 Ronald S. Bultje <rsbultje@gmail.com>
+ *
+ * This file is part of Libav.
+ *
+ * Libav 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.
+ *
+ * Libav 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 Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "atomic.h"
+
+#if !HAVE_MEMORYBARRIER && !HAVE_SYNC_SYNCHRONIZE && !HAVE_MACHINE_RW_BARRIER
+
+#if HAVE_PTHREADS
+
+#include <pthread.h>
+
+static pthread_mutex_t atomic_lock = PTHREAD_MUTEX_INITIALIZER;
+
+int avpriv_atomic_int_get(volatile int *ptr)
+{
+    int res;
+
+    pthread_mutex_lock(&atomic_lock);
+    res = *ptr;
+    pthread_mutex_unlock(&atomic_lock);
+
+    return res;
+}
+
+void avpriv_atomic_int_set(volatile int *ptr, int val)
+{
+    pthread_mutex_lock(&atomic_lock);
+    *ptr = val;
+    pthread_mutex_unlock(&atomic_lock);
+}
+
+int avpriv_atomic_int_add_and_fetch(volatile int *ptr, int inc)
+{
+    int res;
+
+    pthread_mutex_lock(&atomic_lock);
+    *ptr += inc;
+    res = *ptr;
+    pthread_mutex_unlock(&atomic_lock);
+
+    return res;
+}
+
+void *avpriv_atomic_ptr_cas(void * volatile *ptr, void *oldval, void *newval)
+{
+    void *ret;
+    pthread_mutex_lock(&atomic_lock);
+    ret = *ptr;
+    if (*ptr == oldval)
+        *ptr = newval;
+    pthread_mutex_unlock(&atomic_lock);
+    return ret;
+}
+
+#elif !HAVE_THREADS
+
+int avpriv_atomic_int_get(volatile int *ptr)
+{
+    return *ptr;
+}
+
+void avpriv_atomic_int_set(volatile int *ptr, int val)
+{
+    *ptr = val;
+}
+
+int avpriv_atomic_int_add_and_fetch(volatile int *ptr, int inc)
+{
+    *ptr += inc;
+    return *ptr;
+}
+
+void *avpriv_atomic_ptr_cas(void * volatile *ptr, void *oldval, void *newval)
+{
+    if (*ptr == oldval) {
+        *ptr = newval;
+        return oldval;
+    }
+    return *ptr;
+}
+
+#else
+
+#error "Threading is enabled, but there is no implementation of atomic operations available"
+
+#endif /* HAVE_PTHREADS */
+
+#endif /* !HAVE_MEMORYBARRIER && !HAVE_SYNC_SYNCHRONIZE && !HAVE_MACHINE_RW_BARRIER */
+
+#ifdef TEST
+#include <assert.h>
+
+int main(void)
+{
+    volatile int val = 1;
+    int res;
+
+    res = avpriv_atomic_int_add_and_fetch(&val, 1);
+    assert(res == 2);
+    avpriv_atomic_int_set(&val, 3);
+    res = avpriv_atomic_int_get(&val);
+    assert(res == 3);
+
+    return 0;
+}
+#endif