tor-browser

ProfilerBacktrace.h (5896B)

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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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 __PROFILER_BACKTRACE_H
#define __PROFILER_BACKTRACE_H

#include "mozilla/ProfileChunkedBuffer.h"
#include "mozilla/UniquePtr.h"

#include <string>

namespace mozilla {

class TimeStamp;

namespace baseprofiler {

class ProfileBuffer;
class SpliceableJSONWriter;
class ThreadInfo;
class UniqueStacks;

// ProfilerBacktrace encapsulates a synchronous sample.
// It can work with a ProfileBuffer and/or a ProfileChunkedBuffer (if both, they
// must already be linked together). The ProfileChunkedBuffer contains all the
// data; the ProfileBuffer is not strictly needed, only provide it if it is
// already available at the call site.
// And these buffers can either be:
// - owned here, so that the ProfilerBacktrace object can be kept for later
//   use), OR
// - referenced through pointers (in cases where the backtrace is immediately
//   streamed out, so we only need temporary references to external buffers);
//   these pointers may be null for empty backtraces.
class ProfilerBacktrace {
public:
 // Take ownership of external buffers and use them to keep, and to stream a
 // backtrace. If a ProfileBuffer is given, its underlying chunked buffer must
 // be provided as well.
 explicit ProfilerBacktrace(
     const char* aName,
     UniquePtr<ProfileChunkedBuffer> aProfileChunkedBufferStorage,
     UniquePtr<ProfileBuffer> aProfileBufferStorageOrNull = nullptr);

 // Take pointers to external buffers and use them to stream a backtrace.
 // If null, the backtrace is effectively empty.
 // If both are provided, they must already be connected.
 explicit ProfilerBacktrace(
     const char* aName,
     ProfileChunkedBuffer* aExternalProfileChunkedBufferOrNull = nullptr,
     ProfileBuffer* aExternalProfileBufferOrNull = nullptr);

 ~ProfilerBacktrace();

 [[nodiscard]] bool IsEmpty() const {
   return !mProfileChunkedBuffer ||
          ProfileBufferEntryWriter::Serializer<ProfileChunkedBuffer>::Bytes(
              *mProfileChunkedBuffer) <= ULEB128Size(0u);
 }

 // ProfilerBacktraces' stacks are deduplicated in the context of the
 // profile that contains the backtrace as a marker payload.
 //
 // That is, markers that contain backtraces should not need their own stack,
 // frame, and string tables. They should instead reuse their parent
 // profile's tables.
 BaseProfilerThreadId StreamJSON(SpliceableJSONWriter& aWriter,
                                 const TimeStamp& aProcessStartTime,
                                 UniqueStacks& aUniqueStacks);

private:
 // Used to de/serialize a ProfilerBacktrace.
 friend ProfileBufferEntryWriter::Serializer<ProfilerBacktrace>;
 friend ProfileBufferEntryReader::Deserializer<ProfilerBacktrace>;

 std::string mName;

 // `ProfileChunkedBuffer` in which `mProfileBuffer` stores its data; must be
 // located before `mProfileBuffer` so that it's destroyed after.
 UniquePtr<ProfileChunkedBuffer> mOptionalProfileChunkedBufferStorage;
 // If null, there is no need to check mProfileBuffer's (if present) underlying
 // buffer because this is done when constructed.
 ProfileChunkedBuffer* mProfileChunkedBuffer;

 UniquePtr<ProfileBuffer> mOptionalProfileBufferStorage;
 ProfileBuffer* mProfileBuffer;
};

}  // namespace baseprofiler

// Format: [ UniquePtr<BlockRingsBuffer> | name ]
// Initial len==0 marks a nullptr or empty backtrace.
template <>
struct ProfileBufferEntryWriter::Serializer<baseprofiler::ProfilerBacktrace> {
 static Length Bytes(const baseprofiler::ProfilerBacktrace& aBacktrace) {
   if (!aBacktrace.mProfileChunkedBuffer) {
     // No buffer.
     return ULEB128Size(0u);
   }
   auto bufferBytes = SumBytes(*aBacktrace.mProfileChunkedBuffer);
   if (bufferBytes <= ULEB128Size(0u)) {
     // Empty buffer.
     return ULEB128Size(0u);
   }
   return bufferBytes + SumBytes(aBacktrace.mName);
 }

 static void Write(ProfileBufferEntryWriter& aEW,
                   const baseprofiler::ProfilerBacktrace& aBacktrace) {
   if (!aBacktrace.mProfileChunkedBuffer ||
       SumBytes(*aBacktrace.mProfileChunkedBuffer) <= ULEB128Size(0u)) {
     // No buffer, or empty buffer.
     aEW.WriteULEB128(0u);
     return;
   }
   aEW.WriteObject(*aBacktrace.mProfileChunkedBuffer);
   aEW.WriteObject(aBacktrace.mName);
 }
};

template <typename Destructor>
struct ProfileBufferEntryWriter::Serializer<
   UniquePtr<baseprofiler::ProfilerBacktrace, Destructor>> {
 static Length Bytes(const UniquePtr<baseprofiler::ProfilerBacktrace,
                                     Destructor>& aBacktrace) {
   if (!aBacktrace) {
     // Null backtrace pointer (treated like an empty backtrace).
     return ULEB128Size(0u);
   }
   return SumBytes(*aBacktrace);
 }

 static void Write(ProfileBufferEntryWriter& aEW,
                   const UniquePtr<baseprofiler::ProfilerBacktrace,
                                   Destructor>& aBacktrace) {
   if (!aBacktrace) {
     // Null backtrace pointer (treated like an empty backtrace).
     aEW.WriteULEB128(0u);
     return;
   }
   aEW.WriteObject(*aBacktrace);
 }
};

template <typename Destructor>
struct ProfileBufferEntryReader::Deserializer<
   UniquePtr<baseprofiler::ProfilerBacktrace, Destructor>> {
 static void ReadInto(
     ProfileBufferEntryReader& aER,
     UniquePtr<baseprofiler::ProfilerBacktrace, Destructor>& aBacktrace) {
   aBacktrace = Read(aER);
 }

 static UniquePtr<baseprofiler::ProfilerBacktrace, Destructor> Read(
     ProfileBufferEntryReader& aER);
};

}  // namespace mozilla

#endif  // __PROFILER_BACKTRACE_H