opensles: Make sure to only ever create a single engine object

The OpenSL ES spec defines:

An implementation shall enable creation of at least one such object, but
attempting to create more instances (either by a single application or by
several different applications) may fail.

sys/opensles/opensles.c

@@ -21,12 +21,67 @@
 #include "config.h"
 #endif
 
+#include <gst/gst.h>
+#include <SLES/OpenSLES.h>
+
+#include "opensles.h"
 #include "openslessink.h"
 #include "openslessrc.h"
 
+static GMutex engine_mutex;
+static SLObjectItf engine_object = NULL;
+static gint engine_object_refcount = 0;
+
+SLObjectItf
+gst_opensles_get_engine (void)
+{
+  g_mutex_lock (&engine_mutex);
+  if (!engine_object) {
+    SLresult result;
+    result = slCreateEngine (&engine_object, 0, NULL, 0, NULL, NULL);
+    if (result != SL_RESULT_SUCCESS) {
+      GST_ERROR ("slCreateEngine failed(0x%08x)", (guint32) result);
+      engine_object = NULL;
+    }
+
+    result = (*engine_object)->Realize (engine_object, SL_BOOLEAN_FALSE);
+    if (result != SL_RESULT_SUCCESS) {
+      GST_ERROR ("engine.Realize failed(0x%08x)", (guint32) result);
+      (*engine_object)->Destroy (engine_object);
+      engine_object = NULL;
+    }
+  }
+
+  if (engine_object) {
+    engine_object_refcount++;
+  }
+  g_mutex_unlock (&engine_mutex);
+
+  return engine_object;
+}
+
+void
+gst_opensles_release_engine (SLObjectItf engine_object_parameter)
+{
+  g_mutex_lock (&engine_mutex);
+  g_assert (engine_object == engine_object_parameter);
+
+  if (engine_object) {
+    engine_object_refcount--;
+
+    if (engine_object_refcount == 0) {
+      (*engine_object)->Destroy (engine_object);
+      engine_object = NULL;
+    }
+  }
+  g_mutex_unlock (&engine_mutex);
+}
+
 static gboolean
 plugin_init (GstPlugin * plugin)
 {
+  g_mutex_init (&engine_mutex);
+
   if (!gst_element_register (plugin, "openslessink", GST_RANK_PRIMARY,
           GST_TYPE_OPENSLES_SINK)) {
     return FALSE;

sys/opensles/opensles.h

@@ -0,0 +1,30 @@
+/* GStreamer
+ * Copyright (C) 2012 Collabora Ltd.
+ *   Author: Sebastian Dröge <sebastian.droege@collabora.co.uk>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#ifndef __OPENSLES_H__
+#define __OPENSLES_H__
+
+#include <gst/gst.h>
+#include <SLES/OpenSLES.h>
+
+SLObjectItf gst_opensles_get_engine (void);
+void gst_opensles_release_engine (SLObjectItf engine_object);
+
+#endif /* __OPENSLES_H__ */

sys/opensles/openslesringbuffer.c

@@ -21,6 +21,7 @@
 #  include <config.h>
 #endif
 
+#include "opensles.h"
 #include "openslesringbuffer.h"
 
 GST_DEBUG_CATEGORY_STATIC (opensles_ringbuffer_debug);
@@ -683,18 +684,10 @@ gst_opensles_ringbuffer_open_device (GstAudioRingBuffer * rb)
 
   thiz = GST_OPENSLES_RING_BUFFER_CAST (rb);
 
-  /* Create the engine object */
-  result = slCreateEngine (&thiz->engineObject, 0, NULL, 0, NULL, NULL);
-  if (result != SL_RESULT_SUCCESS) {
-    GST_ERROR_OBJECT (thiz, "slCreateEngine failed(0x%08x)", (guint32) result);
-    goto failed;
-  }
-
-  /* Realize the engine object */
-  result = (*thiz->engineObject)->Realize (thiz->engineObject,
-      SL_BOOLEAN_FALSE);
-  if (result != SL_RESULT_SUCCESS) {
-    GST_ERROR_OBJECT (thiz, "engine.Realize failed(0x%08x)", (guint32) result);
+  /* Create and realize the engine object */
+  thiz->engineObject = gst_opensles_get_engine ();
+  if (!thiz->engineObject) {
+    GST_ERROR_OBJECT (thiz, "Failed to get engine object");
     goto failed;
   }
 
@@ -771,7 +764,7 @@ gst_opensles_ringbuffer_close_device (GstAudioRingBuffer * rb)
 
   /* Destroy the engine object and invalidate all associated interfaces */
   if (thiz->engineObject) {
-    (*thiz->engineObject)->Destroy (thiz->engineObject);
+    gst_opensles_release_engine (thiz->engineObject);
     thiz->engineObject = NULL;
     thiz->engineEngine = NULL;
   }

sys/opensles/openslessink.c

@@ -36,6 +36,7 @@
 #  include <config.h>
 #endif
 
+#include "opensles.h"
 #include "openslessink.h"
 
 GST_DEBUG_CATEGORY_STATIC (opensles_sink_debug);
@@ -109,17 +110,10 @@ _opensles_query_capabilities (GstOpenSLESSink * sink)
   SLuint32 outputDeviceIDs[MAX_NUMBER_OUTPUT_DEVICES];
   SLAudioOutputDescriptor audioOutputDescriptor;
 
-  /* Create engine */
-  result = slCreateEngine (&engineObject, 0, NULL, 0, NULL, NULL);
-  if (result != SL_RESULT_SUCCESS) {
-    GST_ERROR_OBJECT (sink, "slCreateEngine failed(0x%08x)", (guint32) result);
-    goto beach;
-  }
-
-  /* Realize the engine */
-  result = (*engineObject)->Realize (engineObject, SL_BOOLEAN_FALSE);
-  if (result != SL_RESULT_SUCCESS) {
-    GST_ERROR_OBJECT (sink, "engine.Realize failed(0x%08x)", (guint32) result);
+  /* Create and realize engine */
+  engineObject = gst_opensles_get_engine ();
+  if (!engineObject) {
+    GST_ERROR_OBJECT (sink, "Getting engine failed");
     goto beach;
   }
 
@@ -171,7 +165,7 @@ _opensles_query_capabilities (GstOpenSLESSink * sink)
 beach:
   /* Destroy the engine object */
   if (engineObject) {
-    (*engineObject)->Destroy (engineObject);
+    gst_opensles_release_engine (engineObject);
   }
 
   return res;