Bug 1213437 - Less data copying when handling structured clones in MessageManager, r=baku

dom/ipc/StructuredCloneData.cpp

@@ -27,21 +27,19 @@ namespace ipc {
 bool
 StructuredCloneData::Copy(const StructuredCloneData& aData)
 {
-  if (!aData.mData) {
+  if (!aData.Data()) {
     return true;
   }
 
-  uint64_t* data = static_cast<uint64_t*>(js_malloc(aData.mDataLength));
-  if (!data) {
-    return false;
+  if (aData.SharedData()) {
+    mSharedData = aData.SharedData();
+  } else {
+    mSharedData =
+      SharedJSAllocatedData::CreateFromExternalData(aData.Data(),
+                                                    aData.DataLength());
+    NS_ENSURE_TRUE(mSharedData, false);
   }
 
-  memcpy(data, aData.mData, aData.mDataLength);
-
-  mData = data;
-  mDataLength = aData.mDataLength;
-  mDataOwned = eJSAllocated;
-
   MOZ_ASSERT(BlobImpls().IsEmpty());
   BlobImpls().AppendElements(aData.BlobImpls());
 
@@ -55,12 +53,12 @@ StructuredCloneData::Read(JSContext* aCx,
                           JS::MutableHandle<JS::Value> aValue,
                           ErrorResult &aRv)
 {
-  MOZ_ASSERT(mData);
+  MOZ_ASSERT(Data());
 
   nsIGlobalObject *global = xpc::NativeGlobal(JS::CurrentGlobalOrNull(aCx));
   MOZ_ASSERT(global);
 
-  ReadFromBuffer(global, aCx, mData, mDataLength, aValue, aRv);
+  ReadFromBuffer(global, aCx, Data(), DataLength(), aValue, aRv);
 }
 
 void
@@ -68,26 +66,28 @@ StructuredCloneData::Write(JSContext* aCx,
                            JS::Handle<JS::Value> aValue,
                            ErrorResult &aRv)
 {
-  MOZ_ASSERT(!mData);
+  MOZ_ASSERT(!Data());
 
   StructuredCloneHolder::Write(aCx, aValue, aRv);
   if (NS_WARN_IF(aRv.Failed())) {
     return;
   }
 
-  mBuffer->steal(&mData, &mDataLength);
+  uint64_t* data = nullptr;
+  size_t dataLength = 0;
+  mBuffer->steal(&data, &dataLength);
   mBuffer = nullptr;
-  mDataOwned = eJSAllocated;
+  mSharedData = new SharedJSAllocatedData(data, dataLength);
 }
 
 void
 StructuredCloneData::WriteIPCParams(Message* aMsg) const
 {
-  WriteParam(aMsg, mDataLength);
+  WriteParam(aMsg, DataLength());
 
-  if (mDataLength) {
+  if (DataLength()) {
     // Structured clone data must be 64-bit aligned.
-    aMsg->WriteBytes(mData, mDataLength, sizeof(uint64_t));
+    aMsg->WriteBytes(Data(), DataLength(), sizeof(uint64_t));
   }
 }
 
@@ -95,31 +95,29 @@ bool
 StructuredCloneData::ReadIPCParams(const IPC::Message* aMsg,
                                    void** aIter)
 {
-  MOZ_ASSERT(!mData);
+  MOZ_ASSERT(!Data());
 
-  if (!ReadParam(aMsg, aIter, &mDataLength)) {
+  size_t dataLength = 0;
+  if (!ReadParam(aMsg, aIter, &dataLength)) {
     return false;
   }
 
-  if (!mDataLength) {
+  if (!dataLength) {
     return true;
   }
 
+  uint64_t* dataBuffer = nullptr;
   const char** buffer =
-    const_cast<const char**>(reinterpret_cast<char**>(&mData));
+    const_cast<const char**>(reinterpret_cast<char**>(&dataBuffer));
   // Structured clone data must be 64-bit aligned.
-  if (!aMsg->ReadBytes(aIter, buffer, mDataLength, sizeof(uint64_t))) {
+  if (!aMsg->ReadBytes(aIter, buffer, dataLength, sizeof(uint64_t))) {
     return false;
   }
 
-  uint64_t* data = static_cast<uint64_t*>(js_malloc(mDataLength));
-  if (!data) {
-     return false;
-  }
+  mSharedData = SharedJSAllocatedData::CreateFromExternalData(dataBuffer,
+                                                              dataLength);
+  NS_ENSURE_TRUE(mSharedData, false);
 
-  memcpy(data, mData, mDataLength);
-  mData = data;
-  mDataOwned = eJSAllocated;
   return true;
 }
 
@@ -127,17 +125,10 @@ bool
 StructuredCloneData::CopyExternalData(const void* aData,
                                       size_t aDataLength)
 {
-  MOZ_ASSERT(!mData);
-  uint64_t* data = static_cast<uint64_t*>(js_malloc(aDataLength));
-  if (!data) {
-     return false;
-  }
-
-  memcpy(data, aData, aDataLength);
-  mData = data;
-  mDataLength = aDataLength;
-  mDataOwned = eJSAllocated;
-
+  MOZ_ASSERT(!Data());
+  mSharedData = SharedJSAllocatedData::CreateFromExternalData(aData,
+                                                              aDataLength);
+  NS_ENSURE_TRUE(mSharedData, false);
   return true;
 }
 

dom/ipc/StructuredCloneData.h

@@ -7,7 +7,10 @@
 #ifndef mozilla_dom_ipc_StructuredCloneData_h
 #define mozilla_dom_ipc_StructuredCloneData_h
 
+#include <algorithm>
+#include "mozilla/RefPtr.h"
 #include "mozilla/dom/StructuredCloneHolder.h"
+#include "nsISupportsImpl.h"
 
 namespace IPC {
 class Message;
@@ -17,6 +20,51 @@ namespace mozilla {
 namespace dom {
 namespace ipc {
 
+class SharedJSAllocatedData final
+{
+public:
+  SharedJSAllocatedData(uint64_t* aData, size_t aDataLength)
+  : mData(aData), mDataLength(aDataLength)
+  {
+    MOZ_ASSERT(mData);
+  }
+
+  static already_AddRefed<SharedJSAllocatedData>
+  CreateFromExternalData(const void* aData, size_t aDataLength)
+  {
+    uint64_t* data = Allocate64bitSafely(aDataLength);
+    if (!data) {
+      return nullptr;
+    }
+
+    memcpy(data, aData, aDataLength);
+    nsRefPtr<SharedJSAllocatedData> sharedData =
+      new SharedJSAllocatedData(data, aDataLength);
+    return sharedData.forget();
+  }
+
+  NS_INLINE_DECL_REFCOUNTING(SharedJSAllocatedData)
+
+  uint64_t* Data() const { return mData; }
+  size_t DataLength() const { return mDataLength; }
+
+private:
+  ~SharedJSAllocatedData()
+  {
+    js_free(mData);
+  }
+
+  static uint64_t*
+  Allocate64bitSafely(size_t aSize)
+  {
+    // Structured cloning requires 64-bit aligment.
+    return static_cast<uint64_t*>(js_malloc(std::max(sizeof(uint64_t), aSize)));
+  }
+
+  uint64_t* mData;
+  size_t mDataLength;
+};
+
 class StructuredCloneData : public StructuredCloneHolder
 {
 public:
@@ -24,18 +72,15 @@ public:
     : StructuredCloneHolder(StructuredCloneHolder::CloningSupported,
                             StructuredCloneHolder::TransferringNotSupported,
                             StructuredCloneHolder::DifferentProcess)
-    , mData(nullptr)
-    , mDataLength(0)
-    , mDataOwned(eNone)
+    , mExternalData(nullptr)
+    , mExternalDataLength(0)
   {}
 
   StructuredCloneData(const StructuredCloneData&) = delete;
 
   ~StructuredCloneData()
   {
-    if (mDataOwned == eJSAllocated) {
-      js_free(mData);
-    }
+    MOZ_ASSERT(!(mExternalData && mSharedData));
   }
 
   StructuredCloneData&
@@ -63,22 +108,26 @@ public:
 
   void UseExternalData(uint64_t* aData, size_t aDataLength)
   {
-    MOZ_ASSERT(!mData);
-    mData = aData;
-    mDataLength = aDataLength;
-    MOZ_ASSERT(mDataOwned == eNone);
+    MOZ_ASSERT(!Data());
+    mExternalData = aData;
+    mExternalDataLength = aDataLength;
   }
 
   bool CopyExternalData(const void* aData, size_t aDataLength);
 
   uint64_t* Data() const
   {
-    return mData;
+    return mSharedData ? mSharedData->Data() : mExternalData;
   }
 
   size_t DataLength() const
   {
-    return mDataLength;
+    return mSharedData ? mSharedData->DataLength() : mExternalDataLength;
+  }
+
+  SharedJSAllocatedData* SharedData() const
+  {
+    return mSharedData;
   }
 
   // For IPC serialization
@@ -86,12 +135,10 @@ public:
   bool ReadIPCParams(const IPC::Message* aMessage, void** aIter);
 
 private:
-  uint64_t* mData;
-  size_t mDataLength;
-  enum {
-    eNone,
-    eJSAllocated,
-  } mDataOwned;
+  uint64_t* MOZ_NON_OWNING_REF mExternalData;
+  size_t mExternalDataLength;
+
+  RefPtr<SharedJSAllocatedData> mSharedData;
 };
 
 } // namespace ipc