1 files changed, 116 insertions, 0 deletions
diff --git a/dom/media/SharedBuffer.h b/dom/media/SharedBuffer.h
new file mode 100644
index 0000000000..d8fa87f9ed
--- /dev/null
+++ b/dom/media/SharedBuffer.h
@@ -0,0 +1,116 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZILLA_SHAREDBUFFER_H_
+#define MOZILLA_SHAREDBUFFER_H_
+
+#include "mozilla/CheckedInt.h"
+#include "mozilla/mozalloc.h"
+#include "mozilla/MemoryReporting.h"
+#include "nsISupportsImpl.h"
+
+namespace mozilla {
+
+class AudioBlockBuffer;
+class ThreadSharedFloatArrayBufferList;
+
+/**
+ * Base class for objects with a thread-safe refcount and a virtual
+ * destructor.
+ */
+class ThreadSharedObject {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ThreadSharedObject)
+
+  bool IsShared() { return mRefCnt.get() > 1; }
+
+  virtual AudioBlockBuffer* AsAudioBlockBuffer() { return nullptr; };
+  virtual ThreadSharedFloatArrayBufferList*
+  AsThreadSharedFloatArrayBufferList() {
+    return nullptr;
+  };
+
+  virtual size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const {
+    return 0;
+  }
+
+  virtual size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const {
+    return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
+  }
+
+ protected:
+  // Protected destructor, to discourage deletion outside of Release():
+  virtual ~ThreadSharedObject() = default;
+};
+
+/**
+ * Heap-allocated chunk of arbitrary data with threadsafe refcounting.
+ * Typically you would allocate one of these, fill it in, and then treat it as
+ * immutable while it's shared.
+ * This only guarantees 4-byte alignment of the data. For alignment we simply
+ * assume that the memory from malloc is at least 4-byte aligned and the
+ * refcount's size is large enough that SharedBuffer's size is divisible by 4.
+ */
+class SharedBuffer : public ThreadSharedObject {
+ public:
+  void* Data() { return this + 1; }
+
+  // Ensure that the caller has a CheckedInt.  We have to take one by
+  // non-const reference to do that, because if we take one by const
+  // reference or value or rvalue reference the implicit constructor on
+  // CheckedInt will helpfully synthesize one for us at the callsite
+  // even if the caller passes a raw size_t.
+  static already_AddRefed<SharedBuffer> Create(CheckedInt<size_t>& aSize,
+                                               const fallible_t&) {
+    CheckedInt<size_t> allocSize = AllocSize(aSize, fallible);
+    if (!allocSize.isValid()) {
+      return nullptr;
+    }
+    void* m = operator new(allocSize.value(), fallible);
+    if (!m) {
+      return nullptr;
+    }
+    RefPtr<SharedBuffer> p = new (m) SharedBuffer();
+    return p.forget();
+  }
+
+  static already_AddRefed<SharedBuffer> Create(CheckedInt<size_t>& aSize) {
+    void* m = operator new(AllocSize(aSize));
+    RefPtr<SharedBuffer> p = new (m) SharedBuffer();
+    return p.forget();
+  }
+
+  size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const override {
+    return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
+  }
+
+ private:
+  static CheckedInt<size_t> AllocSize(CheckedInt<size_t> aDataSize,
+                                      const fallible_t&) {
+    CheckedInt<size_t> size = sizeof(SharedBuffer);
+    size += aDataSize;
+    return size;
+  }
+
+  static size_t AllocSize(CheckedInt<size_t> aDataSize) {
+    CheckedInt<size_t> size = AllocSize(aDataSize, fallible);
+    if (!size.isValid()) {
+      MOZ_CRASH();
+    }
+    return size.value();
+  }
+
+  SharedBuffer() {
+    NS_ASSERTION(
+        (reinterpret_cast<char*>(this + 1) - reinterpret_cast<char*>(this)) %
+                4 ==
+            0,
+        "SharedBuffers should be at least 4-byte aligned");
+  }
+};
+
+}  // namespace mozilla
+
+#endif /* MOZILLA_SHAREDBUFFER_H_ */