RawChannel refactoring

mojo/system/raw_channel_posix.cc

 // Copyright 2013 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 <errno.h>
-#include <string.h>
 #include <unistd.h>
 
-#include <algorithm>
-#include <deque>
-#include <vector>
-
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop/message_loop.h"
 #include "base/posix/eintr_wrapper.h"
-#include "base/stl_util.h"
 #include "base/synchronization/lock.h"
 #include "mojo/system/embedder/platform_handle.h"
-#include "mojo/system/message_in_transit.h"
 
 namespace mojo {
 namespace system {
 
 namespace {
 
-const size_t kReadSize = 4096;
-
 class RawChannelPosix : public RawChannel,
                         public base::MessageLoopForIO::Watcher {
  public:
   RawChannelPosix(embedder::ScopedPlatformHandle handle,
                   Delegate* delegate,
                   base::MessageLoopForIO* message_loop_for_io);
   virtual ~RawChannelPosix();
 
+ private:
   // |RawChannel| implementation:
-  virtual bool Init() OVERRIDE;
-  virtual void Shutdown() OVERRIDE;
-  virtual bool WriteMessage(scoped_ptr<MessageInTransit> message) OVERRIDE;
+  virtual IOResult Read(size_t* bytes_read) OVERRIDE;
+  virtual IOResult ScheduleRead() OVERRIDE;
+  virtual IOResult WriteNoLock(size_t* bytes_written) OVERRIDE;
+  virtual IOResult ScheduleWriteNoLock() OVERRIDE;
+  virtual bool OnInit() OVERRIDE;
+  virtual void OnShutdownNoLock(
+      scoped_ptr<ReadBuffer> read_buffer,
+      scoped_ptr<WriteBuffer> write_buffer) OVERRIDE;
 
- private:
   // |base::MessageLoopForIO::Watcher| implementation:
   virtual void OnFileCanReadWithoutBlocking(int fd) OVERRIDE;
   virtual void OnFileCanWriteWithoutBlocking(int fd) OVERRIDE;
 
   // Watches for |fd_| to become writable. Must be called on the I/O thread.
   void WaitToWrite();
 
-  // Calls |delegate()->OnFatalError(fatal_error)|. Must be called on the I/O
-  // thread WITHOUT |write_lock_| held.
-  void CallOnFatalError(Delegate::FatalError fatal_error);
-
-  // Writes the message at the front of |write_message_queue_|, starting at
-  // |write_message_offset_|. It removes and destroys if the write completes and
-  // otherwise updates |write_message_offset_|. Returns true on success. Must be
-  // called under |write_lock_|.
-  bool WriteFrontMessageNoLock();
-
-  // Cancels all pending writes and destroys the contents of
-  // |write_message_queue_|. Should only be called if |write_stopped_| is false;
-  // sets |write_stopped_| to true. Must be called under |write_lock_|.
-  void CancelPendingWritesNoLock();
-
   embedder::ScopedPlatformHandle fd_;
 
-  // Only used on the I/O thread:
+  // The following members are only used on the I/O thread:
   scoped_ptr<base::MessageLoopForIO::FileDescriptorWatcher> read_watcher_;
   scoped_ptr<base::MessageLoopForIO::FileDescriptorWatcher> write_watcher_;
 
-  // We store data from |read()|s in |read_buffer_|. The start of |read_buffer_|
-  // is always aligned with a message boundary (we will copy memory to ensure
-  // this), but |read_buffer_| may be larger than the actual number of bytes we
-  // have.
-  std::vector<char> read_buffer_;
-  size_t read_buffer_num_valid_bytes_;
+  bool pending_read_;
 
-  base::Lock write_lock_;  // Protects the following members.
-  bool write_stopped_;
-  // TODO(vtl): When C++11 is available, switch this to a deque of
-  // |scoped_ptr|/|unique_ptr|s.
-  std::deque<MessageInTransit*> write_message_queue_;
-  size_t write_message_offset_;
+  // The following members are used on multiple threads and protected by
+  // |write_lock()|:
+  bool pending_write_;
+
   // This is used for posting tasks from write threads to the I/O thread. It
   // must only be accessed under |write_lock_|. The weak pointers it produces
   // are only used/invalidated on the I/O thread.
   base::WeakPtrFactory<RawChannelPosix> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RawChannelPosix);
 };
 
 RawChannelPosix::RawChannelPosix(embedder::ScopedPlatformHandle handle,
                                  Delegate* delegate,
                                  base::MessageLoopForIO* message_loop_for_io)
     : RawChannel(delegate, message_loop_for_io),
       fd_(handle.Pass()),
-      read_buffer_num_valid_bytes_(0),
-      write_stopped_(false),
-      write_message_offset_(0),
+      pending_read_(false),
+      pending_write_(false),
       weak_ptr_factory_(this) {
-  CHECK_EQ(RawChannel::message_loop_for_io()->type(),
-           base::MessageLoop::TYPE_IO);
   DCHECK(fd_.is_valid());
 }
 
 RawChannelPosix::~RawChannelPosix() {
-  DCHECK(write_stopped_);
-  DCHECK(!fd_.is_valid());
+  DCHECK(!pending_read_);
+  DCHECK(!pending_write_);
 
-  // No need to take the |write_lock_| here -- if there are still weak pointers
+  // 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());
 
   // These must have been shut down/destroyed on the I/O thread.
   DCHECK(!read_watcher_.get());
   DCHECK(!write_watcher_.get());
 }
 
-bool RawChannelPosix::Init() {
+RawChannel::IOResult RawChannelPosix::Read(size_t* bytes_read) {
+  DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io());
+  DCHECK(!pending_read_);
+
+  ssize_t read_result = HANDLE_EINTR(
+      read(fd_.get().fd, read_buffer()->GetPosition(),
+           read_buffer()->GetBytesToRead()));
+
+  if (read_result >= 0) {
+    *bytes_read = static_cast<size_t>(read_result);
+    return IO_SUCCEEDED;
+  } else if (errno != EAGAIN && errno != EWOULDBLOCK) {
+    PLOG(ERROR) << "read";
+
+    // Make sure that |OnFileCanReadWithoutBlocking()| won't be called again.
+    read_watcher_.reset();
+
+    return IO_FAILED;
+  }
+
+  return ScheduleRead();
+}
+
+RawChannel::IOResult RawChannelPosix::ScheduleRead() {
+  DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io());
+  DCHECK(!pending_read_);
+
+  pending_read_ = true;
+
+  return IO_PENDING;
+}
+
+RawChannel::IOResult RawChannelPosix::WriteNoLock(size_t* bytes_written) {
+  write_lock().AssertAcquired();
+
+  DCHECK(!pending_write_);
+
+  ssize_t write_result = HANDLE_EINTR(
+      write(fd_.get().fd, write_buffer()->GetPosition(),
+            write_buffer()->GetBytesToWrite()));
+
+  if (write_result >= 0) {
+    *bytes_written = static_cast<size_t>(write_result);
+    return IO_SUCCEEDED;
+  } else if (errno != EAGAIN && errno != EWOULDBLOCK) {
+    PLOG(ERROR) << "write of size " << write_buffer()->GetBytesToWrite();
+    return IO_FAILED;
+  }
+
+  return ScheduleWriteNoLock();
+}
+
+RawChannel::IOResult RawChannelPosix::ScheduleWriteNoLock() {
+  write_lock().AssertAcquired();
+
+  DCHECK(!pending_write_);
+
+  // Set up to wait for the FD to become writable.
+  // If we're not on the I/O thread, we have to post a task to do this.
+  if (base::MessageLoop::current() != message_loop_for_io()) {
+    message_loop_for_io()->PostTask(
+        FROM_HERE,
+        base::Bind(&RawChannelPosix::WaitToWrite,
+                   weak_ptr_factory_.GetWeakPtr()));
+    pending_write_ = true;
+    return IO_PENDING;
+  }
+
+  if (message_loop_for_io()->WatchFileDescriptor(
+      fd_.get().fd, false, base::MessageLoopForIO::WATCH_WRITE,
+      write_watcher_.get(), this)) {
+    pending_write_ = true;
+    return IO_PENDING;
+  }
+
+  return IO_FAILED;
+}
+
+bool RawChannelPosix::OnInit() {
   DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io());
 
   DCHECK(!read_watcher_.get());
   read_watcher_.reset(new base::MessageLoopForIO::FileDescriptorWatcher());
   DCHECK(!write_watcher_.get());
   write_watcher_.reset(new base::MessageLoopForIO::FileDescriptorWatcher());
 
-  // No need to take the lock. No one should be using us yet.
-  DCHECK(write_message_queue_.empty());
-
   if (!message_loop_for_io()->WatchFileDescriptor(fd_.get().fd, true,
           base::MessageLoopForIO::WATCH_READ, read_watcher_.get(), this)) {
     // TODO(vtl): I'm not sure |WatchFileDescriptor()| actually fails cleanly
     // (in the sense of returning the message loop's state to what it was before
     // it was called).
     read_watcher_.reset();
     write_watcher_.reset();
     return false;
   }
 
   return true;
 }
 
-void RawChannelPosix::Shutdown() {
+void RawChannelPosix::OnShutdownNoLock(
+    scoped_ptr<ReadBuffer> /* read_buffer */,

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

nit: In this directory, I've mostly left out spaces inside the /* ... */ (so
/*read_buffer*/).

(The absolute correctness of what I've done is unclear, but consistency is
probably more important here.)

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

Done.

+    scoped_ptr<WriteBuffer> /* write_buffer */) {
   DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io());
-
-  base::AutoLock locker(write_lock_);
-  if (!write_stopped_)
-    CancelPendingWritesNoLock();
+  write_lock().AssertAcquired();
 
   read_watcher_.reset();  // This will stop watching (if necessary).
   write_watcher_.reset();  // This will stop watching (if necessary).
 
+  pending_read_ = false;
+  pending_write_ = false;
+
   DCHECK(fd_.is_valid());
   fd_.reset();
 
   weak_ptr_factory_.InvalidateWeakPtrs();
 }
 
-// Reminder: This must be thread-safe, and takes ownership of |message|.
-bool RawChannelPosix::WriteMessage(scoped_ptr<MessageInTransit> message) {
-  base::AutoLock locker(write_lock_);
-  if (write_stopped_)
-    return false;
-
-  if (!write_message_queue_.empty()) {
-    write_message_queue_.push_back(message.release());
-    return true;
-  }
-
-  write_message_queue_.push_front(message.release());
-  DCHECK_EQ(write_message_offset_, 0u);
-  bool result = WriteFrontMessageNoLock();
-  DCHECK(result || write_message_queue_.empty());
-
-  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(&RawChannelPosix::CallOnFatalError,
-                   weak_ptr_factory_.GetWeakPtr(),
-                   Delegate::FATAL_ERROR_FAILED_WRITE));
-  } else if (!write_message_queue_.empty()) {
-    // Set up to wait for the FD to become writable. If we're not on the I/O
-    // thread, we have to post a task to do this.
-    if (base::MessageLoop::current() == message_loop_for_io()) {
-      WaitToWrite();
-    } else {
-      message_loop_for_io()->PostTask(
-          FROM_HERE,
-          base::Bind(&RawChannelPosix::WaitToWrite,
-                     weak_ptr_factory_.GetWeakPtr()));
-    }
-  }
-
-  return result;
-}
-
 void RawChannelPosix::OnFileCanReadWithoutBlocking(int fd) {
   DCHECK_EQ(fd, fd_.get().fd);
   DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io());
 
-  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;
-  for (;;) {
-    if (read_buffer_.size() - (read_buffer_start + 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_.size(), kReadSize);
-      while (new_size <
-                 read_buffer_start + read_buffer_num_valid_bytes_ + kReadSize)
-        new_size *= 2;
+  if (!pending_read_)
+    return;

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

You should probably DCHECK that read_waiter_ is null (otherwise we could end up
spinning).

...

BUT: Of course you're assuming that |OnReadCompleted()| always schedules another
read on (read) success/failure, which its contract doesn't appear to guarantee.

(E.g., what if there's some condition that causes it to not call
|ScheduleRead()|?)

Sort of the minimum thing you can do here is to |DCHECK()| that |pending_read_|
is true (or that read-watching has been cancelled) after |OnReadComplete()|.

Quite possibly, you should get rid of |pending_read_| and make it so this class
can be aware of/notified when the superclass gives up on reading.

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

Thanks! :)

 
-      // TODO(vtl): It's suboptimal to zero out the fresh memory.
-      read_buffer_.resize(new_size, 0);
-    }
-
-    ssize_t bytes_read = HANDLE_EINTR(
-        read(fd_.get().fd,
-             &read_buffer_[read_buffer_start + read_buffer_num_valid_bytes_],
-             kReadSize));
-    if (bytes_read < 0) {
-      if (errno != EAGAIN && errno != EWOULDBLOCK) {
-        PLOG(ERROR) << "read";
-
-        // Make sure that |OnFileCanReadWithoutBlocking()| won't be called
-        // again.
-        read_watcher_.reset();
-
-        CallOnFatalError(Delegate::FATAL_ERROR_FAILED_READ);
-        return;
-      }
-
-      break;
-    }
-
-    read_buffer_num_valid_bytes_ += static_cast<size_t>(bytes_read);
-
-    // Dispatch all the messages that we can.
-    size_t message_size;
-    // Note that we rely on short-circuit evaluation here:
-    //   - |read_buffer_start| may be an invalid index into |read_buffer_| if
-    //     |read_buffer_num_valid_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 (read_buffer_num_valid_bytes_ > 0 &&
-           MessageInTransit::GetNextMessageSize(
-               &read_buffer_[read_buffer_start], read_buffer_num_valid_bytes_,
-               &message_size) &&
-           read_buffer_num_valid_bytes_ >= message_size) {
-      MessageInTransit message(MessageInTransit::UNOWNED_BUFFER, message_size,
-                               &read_buffer_[read_buffer_start]);
-      DCHECK_EQ(message.main_buffer_size(), message_size);
-
-      // Dispatch the message.
-      delegate()->OnReadMessage(message);
-      if (!read_watcher_.get()) {
-        // |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;
-      read_buffer_num_valid_bytes_ -= message_size;
-    }
-
-    // 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.)
-    if (did_dispatch_message)
-      break;
-
-    // If we didn't max out |kReadSize|, stop reading for now.
-    if (static_cast<size_t>(bytes_read) < kReadSize)
-      break;
-
-    // Else try to read some more....
-  }
-
-  // Move data back to start.
-  if (read_buffer_start > 0) {
-    if (read_buffer_num_valid_bytes_ > 0) {
-      memmove(&read_buffer_[0], &read_buffer_[read_buffer_start],
-              read_buffer_num_valid_bytes_);
-    }
-    read_buffer_start = 0;
-  }
+  pending_read_ = false;
+  size_t bytes_read = 0;
+  IOResult result = Read(&bytes_read);
+  if (result != IO_PENDING)
+    OnReadCompleted(result == IO_SUCCEEDED, bytes_read);
 }
 
 void RawChannelPosix::OnFileCanWriteWithoutBlocking(int fd) {
   DCHECK_EQ(fd, fd_.get().fd);
   DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io());
 
-  bool did_fail = false;
+  IOResult result = IO_FAILED;
+  size_t bytes_written = 0;
   {
-    base::AutoLock locker(write_lock_);
-    DCHECK_EQ(write_stopped_, write_message_queue_.empty());
+    base::AutoLock locker(write_lock());
 
-    if (write_stopped_) {
-      write_watcher_.reset();
+    if (!pending_write_)
       return;

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

"

(though the situation for pending_write_ isn't quite so bad, since
write-watching is one-shot, not persistent.

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

Right. I made it a DCHECK().

-    }
 
-    bool result = WriteFrontMessageNoLock();
-    DCHECK(result || write_message_queue_.empty());
+    pending_write_ = false;
+    result = WriteNoLock(&bytes_written);
+  }
 
-    if (!result) {
-      did_fail = true;
-      write_watcher_.reset();
-    } else if (!write_message_queue_.empty()) {
-      WaitToWrite();
-    }
-  }
-  if (did_fail)
-    CallOnFatalError(Delegate::FATAL_ERROR_FAILED_WRITE);
+  if (result != IO_PENDING)
+    OnWriteCompleted(result == IO_SUCCEEDED, bytes_written);
 }
 
 void RawChannelPosix::WaitToWrite() {
   DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io());
 
   DCHECK(write_watcher_.get());
-  bool result = message_loop_for_io()->WatchFileDescriptor(
-      fd_.get().fd, false, base::MessageLoopForIO::WATCH_WRITE,
-      write_watcher_.get(), this);
-  DCHECK(result);
-}
 
-void RawChannelPosix::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);
-}
+  if (!message_loop_for_io()->WatchFileDescriptor(
+          fd_.get().fd, false, base::MessageLoopForIO::WATCH_WRITE,
+          write_watcher_.get(), this)) {
+    {
+      base::AutoLock locker(write_lock());
 
-bool RawChannelPosix::WriteFrontMessageNoLock() {
-  write_lock_.AssertAcquired();
-
-  DCHECK(!write_stopped_);
-  DCHECK(!write_message_queue_.empty());
-
-  MessageInTransit* message = write_message_queue_.front();
-  DCHECK_LT(write_message_offset_, message->main_buffer_size());
-  size_t bytes_to_write = message->main_buffer_size() - write_message_offset_;
-  ssize_t bytes_written = HANDLE_EINTR(
-      write(fd_.get().fd,
-            static_cast<const char*>(message->main_buffer()) +
-                write_message_offset_,
-            bytes_to_write));
-  if (bytes_written < 0) {
-    if (errno != EAGAIN && errno != EWOULDBLOCK) {
-      PLOG(ERROR) << "write of size " << bytes_to_write;
-      CancelPendingWritesNoLock();
-      return false;
+      DCHECK(pending_write_);
+      pending_write_ = false;
     }
-
-    // We simply failed to write since we'd block. The logic is the same as if
-    // we got a partial write.
-    bytes_written = 0;
+    OnWriteCompleted(false, 0);
   }
-
-  DCHECK_GE(bytes_written, 0);
-  if (static_cast<size_t>(bytes_written) < bytes_to_write) {
-    // Partial (or no) write.
-    write_message_offset_ += static_cast<size_t>(bytes_written);
-  } else {
-    // Complete write.
-    DCHECK_EQ(static_cast<size_t>(bytes_written), bytes_to_write);
-    write_message_queue_.pop_front();
-    delete message;
-    write_message_offset_ = 0;
-  }
-
-  return true;
-}
-
-void RawChannelPosix::CancelPendingWritesNoLock() {
-  write_lock_.AssertAcquired();
-  DCHECK(!write_stopped_);
-
-  write_stopped_ = true;
-  STLDeleteElements(&write_message_queue_);
 }
 
 }  // namespace
 
 // -----------------------------------------------------------------------------
 
 // Static factory method declared in raw_channel.h.
 // static
 RawChannel* RawChannel::Create(embedder::ScopedPlatformHandle handle,
                                Delegate* delegate,
                                base::MessageLoopForIO* message_loop_for_io) {
   return new RawChannelPosix(handle.Pass(), delegate, message_loop_for_io);
 }
 
 }  // namespace system
 }  // namespace mojo