1 files changed, 126 insertions, 0 deletions
diff --git a/tools/profiler/core/ProfileJSONWriter.h b/tools/profiler/core/ProfileJSONWriter.h
new file mode 100644
index 000000000..d9e2115f9
--- /dev/null
+++ b/tools/profiler/core/ProfileJSONWriter.h
@@ -0,0 +1,126 @@
+/* -*- 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 PROFILEJSONWRITER_H
+#define PROFILEJSONWRITER_H
+
+#include <ostream>
+#include <string>
+#include <string.h>
+
+#include "mozilla/JSONWriter.h"
+#include "mozilla/UniquePtr.h"
+
+class SpliceableChunkedJSONWriter;
+
+// On average, profile JSONs are large enough such that we want to avoid
+// reallocating its buffer when expanding. Additionally, the contents of the
+// profile are not accessed until the profile is entirely written. For these
+// reasons we use a chunked writer that keeps an array of chunks, which is
+// concatenated together after writing is finished.
+class ChunkedJSONWriteFunc : public mozilla::JSONWriteFunc
+{
+public:
+  friend class SpliceableJSONWriter;
+
+  ChunkedJSONWriteFunc() {
+    AllocChunk(kChunkSize);
+  }
+
+  bool IsEmpty() const {
+    MOZ_ASSERT_IF(!mChunkPtr, !mChunkEnd &&
+                              mChunkList.length() == 0 &&
+                              mChunkLengths.length() == 0);
+    return !mChunkPtr;
+  }
+
+  void Write(const char* aStr) override;
+  mozilla::UniquePtr<char[]> CopyData() const;
+  void Take(ChunkedJSONWriteFunc&& aOther);
+
+private:
+  void AllocChunk(size_t aChunkSize);
+
+  static const size_t kChunkSize = 4096 * 512;
+
+  // Pointer for writing inside the current chunk.
+  //
+  // The current chunk is always at the back of mChunkList, i.e.,
+  // mChunkList.back() <= mChunkPtr <= mChunkEnd.
+  char* mChunkPtr;
+
+  // Pointer to the end of the current chunk.
+  //
+  // The current chunk is always at the back of mChunkList, i.e.,
+  // mChunkEnd >= mChunkList.back() + mChunkLengths.back().
+  char* mChunkEnd;
+
+  // List of chunks and their lengths.
+  //
+  // For all i, the length of the string in mChunkList[i] is
+  // mChunkLengths[i].
+  mozilla::Vector<mozilla::UniquePtr<char[]>> mChunkList;
+  mozilla::Vector<size_t> mChunkLengths;
+};
+
+struct OStreamJSONWriteFunc : public mozilla::JSONWriteFunc
+{
+  explicit OStreamJSONWriteFunc(std::ostream& aStream)
+    : mStream(aStream)
+  { }
+
+  void Write(const char* aStr) override {
+    mStream << aStr;
+  }
+
+  std::ostream& mStream;
+};
+
+class SpliceableJSONWriter : public mozilla::JSONWriter
+{
+public:
+  explicit SpliceableJSONWriter(mozilla::UniquePtr<mozilla::JSONWriteFunc> aWriter)
+    : JSONWriter(mozilla::Move(aWriter))
+  { }
+
+  void StartBareList(CollectionStyle aStyle = SingleLineStyle) {
+    StartCollection(nullptr, "", aStyle);
+  }
+
+  void EndBareList() {
+    EndCollection("");
+  }
+
+  void NullElements(uint32_t aCount) {
+    for (uint32_t i = 0; i < aCount; i++) {
+      NullElement();
+    }
+  }
+
+  void Splice(const ChunkedJSONWriteFunc* aFunc);
+  void Splice(const char* aStr);
+
+  // Takes the chunks from aFunc and write them. If move is not possible
+  // (e.g., using OStreamJSONWriteFunc), aFunc's chunks are copied and its
+  // storage cleared.
+  virtual void TakeAndSplice(ChunkedJSONWriteFunc* aFunc);
+};
+
+class SpliceableChunkedJSONWriter : public SpliceableJSONWriter
+{
+public:
+  explicit SpliceableChunkedJSONWriter()
+    : SpliceableJSONWriter(mozilla::MakeUnique<ChunkedJSONWriteFunc>())
+  { }
+
+  ChunkedJSONWriteFunc* WriteFunc() const {
+    return static_cast<ChunkedJSONWriteFunc*>(JSONWriter::WriteFunc());
+  }
+
+  // Adopts the chunks from aFunc without copying.
+  virtual void TakeAndSplice(ChunkedJSONWriteFunc* aFunc) override;
+};
+
+#endif // PROFILEJSONWRITER_H