RawChannel refactoring

mojo/system/raw_channel.cc

+// Copyright 2014 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.
+
+#include "mojo/system/raw_channel.h"
+
+#include <string.h>
+
+#include <algorithm>
+
+#include "base/bind.h"
+#include "base/location.h"
+#include "base/logging.h"
+#include "base/message_loop/message_loop.h"
+#include "base/stl_util.h"
+#include "mojo/system/message_in_transit.h"
+
+namespace mojo {
+namespace system {
+
+namespace {

[viettrungluu, 2014/02/26 23:03:39]

Note that this anonymous namespace is redundant. (In C++, const globals have
internal linkage by default.) <shrug>

[yzshen1, 2014/02/27 02:00:30]

Done.

+
+const size_t kReadSize = 4096;
+
+}  // namespace
+
+
+RawChannel::ReadBuffer::ReadBuffer() : buffer_(kReadSize), num_valid_bytes_(0) {
+}
+
+RawChannel::ReadBuffer::~ReadBuffer() {}
+
+char* RawChannel::ReadBuffer::GetPosition() {
+  DCHECK_GE(buffer_.size(), num_valid_bytes_ + kReadSize);
+  return &buffer_[0] + num_valid_bytes_;
+}
+
+size_t RawChannel::ReadBuffer::GetBytesToRead() const {
+  DCHECK_GE(buffer_.size(), num_valid_bytes_ + kReadSize);
+  return kReadSize;
+}
+
+RawChannel::WriteBuffer::WriteBuffer() : offset_(0) {}
+
+RawChannel::WriteBuffer::~WriteBuffer() {
+  STLDeleteElements(&message_queue_);
+}
+
+const char* RawChannel::WriteBuffer::GetPosition() const {
+  if (message_queue_.empty())
+    return NULL;
+
+  DCHECK_GT(message_queue_.front()->main_buffer_size(), offset_);
+  return static_cast<const char*>(message_queue_.front()->main_buffer()) +
+      offset_;
+}
+
+size_t RawChannel::WriteBuffer::GetBytesToWrite() const {
+  if (message_queue_.empty())
+    return 0;
+
+  DCHECK_GT(message_queue_.front()->main_buffer_size(), offset_);
+  return message_queue_.front()->main_buffer_size() - offset_;
+}
+
+RawChannel::RawChannel(Delegate* delegate,
+                       base::MessageLoopForIO* message_loop_for_io)
+    : delegate_(delegate),
+      read_stopped_(false),
+      message_loop_for_io_(message_loop_for_io),
+      write_stopped_(false),
+      weak_ptr_factory_(this) {
+}
+
+RawChannel::~RawChannel() {
+  DCHECK(!read_buffer_);
+  DCHECK(!write_buffer_);
+
+  // No need to take the |write_lock_| here -- if there are still weak pointers
+  // outstanding, then we're hosed anyway (since we wouldn't be able to
+  // invalidate them cleanly, since we might not be on the I/O thread).
+  DCHECK(!weak_ptr_factory_.HasWeakPtrs());
+}
+
+bool RawChannel::Init() {
+  DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io_);
+
+  // No need to take the lock. No one should be using us yet.
+  DCHECK(!read_buffer_);
+  read_buffer_.reset(new ReadBuffer);
+  DCHECK(!write_buffer_);
+  write_buffer_.reset(new WriteBuffer);
+
+  if (!OnInit())
+    return false;
+
+  IOResult result = ScheduleRead();
+  return result == IO_PENDING;

[viettrungluu, 2014/02/26 23:03:39]

nit: I think you may as well write this as |return ScheduleRead() ==
IO_PENDING;| (unless you want to rename "result" to "io_result")

[yzshen1, 2014/02/27 02:00:30]

Done.

+}
+
+void RawChannel::Shutdown() {
+  DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io_);
+
+  base::AutoLock locker(write_lock_);
+
+  weak_ptr_factory_.InvalidateWeakPtrs();
+
+  read_stopped_ = true;
+  write_stopped_ = true;
+
+  OnShutdownNoLock(read_buffer_.Pass(), write_buffer_.Pass());
+}
+
+// Reminder: This must be thread-safe, and takes ownership of |message|.

[viettrungluu, 2014/02/26 23:03:39]

You can get rid of the ", and takes ownership ..." part.

[yzshen1, 2014/02/27 02:00:30]

Done.

+bool RawChannel::WriteMessage(scoped_ptr<MessageInTransit> message) {
+  base::AutoLock locker(write_lock_);
+  if (write_stopped_)
+    return false;
+
+  if (!write_buffer_->message_queue_.empty()) {
+    write_buffer_->message_queue_.push_back(message.release());
+    return true;
+  }
+
+  write_buffer_->message_queue_.push_front(message.release());
+  DCHECK_EQ(write_buffer_->offset_, 0u);
+
+  size_t bytes_written = 0;
+  IOResult io_result = WriteNoLock(&bytes_written);
+  if (io_result == IO_PENDING)
+    return true;
+
+  bool result = OnWriteCompletedNoLock(io_result == IO_SUCCEEDED,
+                                       bytes_written);
+  if (!result) {
+    // Even if we're on the I/O thread, don't call |OnFatalError()| in the
+    // nested context.
+    message_loop_for_io_->PostTask(
+        FROM_HERE,
+        base::Bind(&RawChannel::CallOnFatalError,
+                   weak_ptr_factory_.GetWeakPtr(),
+                   Delegate::FATAL_ERROR_FAILED_WRITE));
+  }
+
+  return result;
+}
+
+RawChannel::ReadBuffer* RawChannel::read_buffer() {
+  DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io_);
+  return read_buffer_.get();
+}
+
+RawChannel::WriteBuffer* RawChannel::write_buffer() {
+  write_lock_.AssertAcquired();
+  return write_buffer_.get();
+}
+
+void RawChannel::OnReadCompleted(bool result, size_t bytes_read) {

[viettrungluu, 2014/02/26 23:03:39]

The implementation of this function could use a comment outlining its general
structure.

[yzshen1, 2014/02/27 02:00:30]

Done.

+  DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io_);
+
+  if (read_stopped_) {
+    NOTREACHED();
+    return;
+  }
+
+  IOResult io_result = result ? IO_SUCCEEDED : IO_FAILED;
+  for (;;) {
+    if (io_result != IO_SUCCEEDED) {
+      read_stopped_ = true;
+      CallOnFatalError(Delegate::FATAL_ERROR_FAILED_READ);
+      return;
+    }
+
+    read_buffer_->num_valid_bytes_ += bytes_read;
+
+    // Dispatch all the messages that we can.
+    bool did_dispatch_message = false;
+    // Tracks the offset of the first undispatched message in |read_buffer_|.
+    // Currently, we copy data to ensure that this is zero at the beginning.
+    size_t read_buffer_start = 0;
+    size_t remaining_bytes = read_buffer_->num_valid_bytes_;
+    size_t message_size;
+    // Note that we rely on short-circuit evaluation here:
+    //   - |read_buffer_start| may be an invalid index into
+    //     |read_buffer_->buffer_| if |remaining_bytes| is zero.
+    //   - |message_size| is only valid if |GetNextMessageSize()| returns true.
+    // TODO(vtl): Use |message_size| more intelligently (e.g., to request the
+    // next read).
+    while (remaining_bytes > 0 &&
+           MessageInTransit::GetNextMessageSize(
+               &read_buffer_->buffer_[read_buffer_start], remaining_bytes,
+               &message_size) &&
+           remaining_bytes >= message_size) {
+      MessageInTransit message(MessageInTransit::UNOWNED_BUFFER, message_size,
+                               &read_buffer_->buffer_[read_buffer_start]);
+      DCHECK_EQ(message.main_buffer_size(), message_size);
+
+      // Dispatch the message.
+      delegate_->OnReadMessage(message);
+      if (read_stopped_) {
+        // |Shutdown()| was called in |OnReadMessage()|.
+        // TODO(vtl): Add test for this case.
+        return;
+      }
+      did_dispatch_message = true;
+
+      // Update our state.
+      read_buffer_start += message_size;
+      remaining_bytes -= message_size;
+    }
+
+    if (read_buffer_start > 0) {
+      // Move data back to start.
+      read_buffer_->num_valid_bytes_ = remaining_bytes;
+      if (read_buffer_->num_valid_bytes_ > 0) {
+        memmove(&read_buffer_->buffer_[0],
+                &read_buffer_->buffer_[read_buffer_start], remaining_bytes);
+      }
+      read_buffer_start = 0;
+    }
+
+    if (read_buffer_->buffer_.size() - read_buffer_->num_valid_bytes_ <
+            kReadSize) {
+      // Use power-of-2 buffer sizes.
+      // TODO(vtl): Make sure the buffer doesn't get too large (and enforce the
+      // maximum message size to whatever extent necessary).
+      // TODO(vtl): We may often be able to peek at the header and get the real
+      // required extra space (which may be much bigger than |kReadSize|).
+      size_t new_size = std::max(read_buffer_->buffer_.size(), kReadSize);
+      while (new_size < read_buffer_->num_valid_bytes_ + kReadSize)
+        new_size *= 2;
+
+      // TODO(vtl): It's suboptimal to zero out the fresh memory.
+      read_buffer_->buffer_.resize(new_size, 0);
+    }
+
+    // (1) If we dispatched any messages, stop reading for now (and let the
+    // message loop do its thing for another round).
+    // TODO(vtl): Is this the behavior we want? (Alternatives: i. Dispatch only
+    // a single message. Risks: slower, more complex if we want to avoid lots of
+    // copying. ii. Keep reading until there's no more data and dispatch all the
+    // messages we can. Risks: starvation of other users of the message loop.)
+    // (2) If we didn't max out |kReadSize|, stop reading for now.
+    bool schedule_for_later = did_dispatch_message || bytes_read < kReadSize;
+    bytes_read = 0;
+    io_result = schedule_for_later ? ScheduleRead() : Read(&bytes_read);
+
+    if (io_result == IO_PENDING)

[viettrungluu, 2014/02/26 23:03:39]

do { ... } while (io_result != IO_PENDING);

[yzshen1, 2014/02/27 02:00:30]

Done.

+      return;
+  }
+}
+
+void RawChannel::OnWriteCompleted(bool result, size_t bytes_written) {
+  DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io_);
+
+  bool did_fail = false;
+  {
+    base::AutoLock locker(write_lock_);
+    DCHECK_EQ(write_stopped_, write_buffer_->message_queue_.empty());
+
+    if (write_stopped_) {
+      NOTREACHED();
+      return;
+    }
+
+    did_fail = !OnWriteCompletedNoLock(result, bytes_written);
+  }
+
+  if (did_fail)
+    CallOnFatalError(Delegate::FATAL_ERROR_FAILED_WRITE);
+}
+
+void RawChannel::CallOnFatalError(Delegate::FatalError fatal_error) {
+  DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io_);
+  // TODO(vtl): Add a "write_lock_.AssertNotAcquired()"?
+  delegate_->OnFatalError(fatal_error);
+}
+
+bool RawChannel::OnWriteCompletedNoLock(bool result, size_t bytes_written) {
+  write_lock_.AssertAcquired();
+
+  DCHECK(!write_stopped_);
+  DCHECK(!write_buffer_->message_queue_.empty());
+
+  if (result) {
+    if (bytes_written < write_buffer_->GetBytesToWrite()) {
+      // Partial (or no) write.
+      write_buffer_->offset_ += bytes_written;
+    } else {
+      // Complete write.
+      DCHECK_EQ(bytes_written, write_buffer_->GetBytesToWrite());
+      delete write_buffer_->message_queue_.front();
+      write_buffer_->message_queue_.pop_front();
+      write_buffer_->offset_ = 0;
+    }
+
+    if (write_buffer_->message_queue_.empty())
+      return true;
+
+    // Schedule the next write.
+    if (ScheduleWriteNoLock() == IO_PENDING)
+      return true;
+  }
+
+  write_stopped_ = true;
+  STLDeleteElements(&write_buffer_->message_queue_);

[viettrungluu, 2014/02/26 23:03:39]

Can't you just do |write_buffer_.reset()| here?

[yzshen1, 2014/02/27 02:00:30]

I was thinking maybe it is good to always give the subclasses the same
WriteBuffer object (via write_buffer() or the parameter of OnShutdownNoLock()).
What do you think?

+  write_buffer_->offset_ = 0;
+  return false;

[viettrungluu, 2014/02/26 23:03:39]

More importantly, if it's the subclass that calls |OnWriteCompletedNoLock()|,
don't you fail to call OnFatalError()?

[yzshen1, 2014/02/27 02:00:30]

OnWriteCompletedNoLock() is a private helper method, which won't be called by
subclasses.

+}
+
+}  // namespace system
+}  // namespace mojo