bug 1199559 add a helper to fallibly allocate ThreadSharedFloatArrayBufferList with buffers r=padenot

--HG--
extra : rebase_source : f7d532fb2142624b0a3c3423c954a2e817d529ea

dom/media/webaudio/AudioNodeEngine.cpp

@@ -12,6 +12,26 @@
 
 namespace mozilla {
 
+already_AddRefed<ThreadSharedFloatArrayBufferList>
+ThreadSharedFloatArrayBufferList::Create(uint32_t aChannelCount,
+                                         size_t aLength,
+                                         const mozilla::fallible_t&)
+{
+  nsRefPtr<ThreadSharedFloatArrayBufferList> buffer =
+    new ThreadSharedFloatArrayBufferList(aChannelCount);
+
+  for (uint32_t i = 0; i < aChannelCount; ++i) {
+    float* channelData = js_pod_malloc<float>(aLength);
+    if (!channelData) {
+      return nullptr;
+    }
+
+    buffer->SetData(i, channelData, js_free, channelData);
+  }
+
+  return buffer.forget();
+}
+
 void
 AllocateAudioBlock(uint32_t aChannelCount, AudioChunk* aChunk)
 {

dom/media/webaudio/AudioNodeEngine.h

@@ -31,12 +31,19 @@ class ThreadSharedFloatArrayBufferList final : public ThreadSharedObject
 {
 public:
   /**
-   * Construct with null data.
+   * Construct with null channel data pointers.
    */
   explicit ThreadSharedFloatArrayBufferList(uint32_t aCount)
   {
     mContents.SetLength(aCount);
   }
+  /**
+   * Create with buffers suitable for transfer to
+   * JS_NewArrayBufferWithContents().  The buffer contents are uninitialized
+   * and so should be set using GetDataForWrite().
+   */
+  static already_AddRefed<ThreadSharedFloatArrayBufferList>
+  Create(uint32_t aChannelCount, size_t aLength, const mozilla::fallible_t&);
 
   struct Storage final
   {