components/services/heap_profiling/public/cpp/sender_pipe.h

// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COMPONENTS_SERVICES_HEAP_PROFILING_PUBLIC_CPP_SENDER_PIPE_H_
#define COMPONENTS_SERVICES_HEAP_PROFILING_PUBLIC_CPP_SENDER_PIPE_H_

#include "build/build_config.h"

#include "base/files/platform_file.h"
#include "base/macros.h"
#include "base/synchronization/lock.h"
#include "mojo/public/cpp/platform/platform_handle.h"

namespace heap_profiling {

class SenderPipe {
 public:
  // 64k is a convenient pipe buffer size.
  // On macOS, the default pipe buffer size is 16 * 1024, but grows to 64 * 1024
  // for large writes. See BIG_PIPE_SIZE.
  // https://opensource.apple.com/source/xnu/xnu-1504.9.37/bsd/sys/pipe.h
  // On Linux [since 2.6.11], the default pipe buffer size is 64 * 1024. See
  // https://linux.die.net/man/7/pipe
  // On Windows, the pipe buffer size is configurable.
  static constexpr size_t kPipeSize = 64 * 1024;

  class PipePair {
   public:
    // Returns a pair of newly created pipes. Must be called from a privileged
    // process. The sender-pipe is non-blocking and has a buffer size of
    // |kPipeSize|.
    PipePair();
    PipePair(PipePair&&);
    mojo::PlatformHandle PassSender() { return std::move(sender_); }
    mojo::PlatformHandle PassReceiver() { return std::move(receiver_); }

   private:
    mojo::PlatformHandle sender_;
    mojo::PlatformHandle receiver_;
    DISALLOW_COPY_AND_ASSIGN(PipePair);
  };

  explicit SenderPipe(mojo::PlatformHandle handle);
  ~SenderPipe();

  enum class Result { kSuccess, kTimeout, kError };

  // Attempts to atomically write all the |data| into the pipe. kError is
  // returned on failure, kTimeout after |timeout_ms| milliseconds.
  Result Send(const void* data, size_t sz, int timeout_ms);

  // Closes the underlying pipe.
  void Close();

 private:
  base::ScopedPlatformFile file_;

  // All calls to Send() are wrapped in a Lock, since the size of the data might
  // be larger than the maximum atomic write size of a pipe on Posix [PIPE_BUF].
  // On Windows, ::WriteFile() is not thread-safe.
  base::Lock lock_;

  DISALLOW_COPY_AND_ASSIGN(SenderPipe);
};

}  // namespace heap_profiling

#endif  // COMPONENTS_SERVICES_HEAP_PROFILING_PUBLIC_CPP_SENDER_PIPE_H_