[webaudio] Fix up ReverbInputBuffer's writeIndex.

2 files changed, 13 insertions, 11 deletions

diff --git a/dom/media/webaudio/blink/ReverbInputBuffer.cpp b/dom/media/webaudio/blink/ReverbInputBuffer.cpp
index 8221f8151d..6b8e642d27 100644
--- a/dom/media/webaudio/blink/ReverbInputBuffer.cpp
+++ b/dom/media/webaudio/blink/ReverbInputBuffer.cpp
@@ -42,19 +42,20 @@ ReverbInputBuffer::ReverbInputBuffer(size_t length)
 
 void ReverbInputBuffer::write(const float* sourceP, size_t numberOfFrames)
 {
-    size_t bufferLength = m_buffer.Length();
-    bool isCopySafe = m_writeIndex + numberOfFrames <= bufferLength;
-    MOZ_ASSERT(isCopySafe);
-    if (!isCopySafe)
-        return;
+  // m_writeIndex is atomic and checked by other threads, so only touch
+  // it at the start and end.
+  size_t index = m_writeIndex;
+
+  size_t bufferLength = m_buffer.Length();
+  size_t newIndex = index + numberOfFrames;
 
-    memcpy(m_buffer.Elements() + m_writeIndex, sourceP, sizeof(float) * numberOfFrames);
+  MOZ_RELEASE_ASSERT(newIndex <= bufferLength);
 
-    m_writeIndex += numberOfFrames;
-    MOZ_ASSERT(m_writeIndex <= bufferLength);
+  memcpy(m_buffer.Elements() + index, sourceP, sizeof(float) * numberOfFrames);
 
-    if (m_writeIndex >= bufferLength)
-        m_writeIndex = 0;
+  if (newIndex >= bufferLength) {
+    m_writeIndex = 0;
+  }
 }
 
 float* ReverbInputBuffer::directReadFrom(int* readIndex, size_t numberOfFrames)
diff --git a/dom/media/webaudio/blink/ReverbInputBuffer.h b/dom/media/webaudio/blink/ReverbInputBuffer.h
index 906021c0d1..f51aa30916 100644
--- a/dom/media/webaudio/blink/ReverbInputBuffer.h
+++ b/dom/media/webaudio/blink/ReverbInputBuffer.h
@@ -30,6 +30,7 @@
 #define ReverbInputBuffer_h
 
 #include "nsTArray.h"
+#include "mozilla/Atomics.h"
 #include "mozilla/MemoryReporting.h"
 
 namespace WebCore {
@@ -63,7 +64,7 @@ public:
 
 private:
     nsTArray<float> m_buffer;
-    size_t m_writeIndex;
+    mozilla::Atomic<size_t, mozilla::ReleaseAcquire> m_writeIndex;
 };
 
 } // namespace WebCore