Deciding best connection to schedule requests on based on cwnd and idle time

net/socket/tcp_client_socket_win.cc

 // Copyright (c) 2011 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 "net/socket/tcp_client_socket_win.h"
 
 #include <mstcpip.h>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
@@ skipping 469 matching lines @@
   core_ = new Core(this);
 
   // WSACreateEvent creates a manual-reset event object.
   core_->read_overlapped_.hEvent = WSACreateEvent();
   // WSAEventSelect sets the socket to non-blocking mode as a side effect.
   // Our connect() and recv() calls require that the socket be non-blocking.
   WSAEventSelect(socket_, core_->read_overlapped_.hEvent, FD_CONNECT);
 
   core_->write_overlapped_.hEvent = WSACreateEvent();
 
+  connect_start_time_ = base::Time::Now();
   if (!connect(socket_, ai->ai_addr, static_cast<int>(ai->ai_addrlen))) {
     // Connected without waiting!
     //
     // The MSDN page for connect says:
     //   With a nonblocking socket, the connection attempt cannot be completed
     //   immediately. In this case, connect will return SOCKET_ERROR, and
     //   WSAGetLastError will return WSAEWOULDBLOCK.
     // which implies that for a nonblocking socket, connect never returns 0.
     // It's not documented whether the event object will be signaled or not
     // if connect does return 0.  So the code below is essentially dead code
@@ skipping 18 matching lines @@
 int TCPClientSocketWin::DoConnectComplete(int result) {
   // Log the end of this attempt (and any OS error it threw).
   int os_error = connect_os_error_;
   connect_os_error_ = 0;
   scoped_refptr<NetLog::EventParameters> params;
   if (result != OK)
     params = new NetLogIntegerParameter("os_error", os_error);
   net_log_.EndEvent(NetLog::TYPE_TCP_CONNECT_ATTEMPT, params);
 
   if (result == OK) {
+    rtt_ms_ = static_cast<double>((base::Time::Now() -
+                                   connect_start_time_).InMicroseconds())
+        / 1000.0;

[willchan no longer on Chromium, 2011/06/09 15:08:54]

same comments as in the libevent socket

[Gagan, 2011/06/09 19:49:26]

please let me know if you prefer rtt in microseconds.

[willchan no longer on Chromium, 2011/06/10 15:05:55]

milliseconds makes sense to me.

[Gagan, 2011/06/10 17:44:17]

I changed it to micros in the last patch. It allows extra precision so that
round off errors will not be prevalent when rtt is low.
I hope you are okay with it, please let me know if you strongly feel against it.

     use_history_.set_was_ever_connected();
     return OK;  // Done!
   }
 
   // Close whatever partially connected socket we currently have.
   DoDisconnect();
 
   // Try to fall back to the next address in the list.
   if (current_ai_->ai_next) {
     next_connect_state_ = CONNECT_STATE_CONNECT;
@@ skipping 146 matching lines @@
     if (ResetEventIfSignaled(core_->read_overlapped_.hEvent)) {
       // Because of how WSARecv fills memory when used asynchronously, Purify
       // isn't able to detect that it's been initialized, so it scans for 0xcd
       // in the buffer and reports UMRs (uninitialized memory reads) for those
       // individual bytes. We override that in PURIFY builds to avoid the
       // false error reports.
       // See bug 5297.
       base::MemoryDebug::MarkAsInitialized(core_->read_buffer_.buf, num);
       base::StatsCounter read_bytes("tcp.read_bytes");
       read_bytes.Add(num);
+      num_bytes_read_ += num;
       if (num > 0)
         use_history_.set_was_used_to_convey_data();
       net_log_.AddByteTransferEvent(NetLog::TYPE_SOCKET_BYTES_RECEIVED, num,
                                     core_->read_buffer_.buf);
       return static_cast<int>(num);
     }
   } else {
     int os_error = WSAGetLastError();
     if (os_error != WSA_IO_PENDING)
       return MapSystemError(os_error);
@@ skipping 150 matching lines @@
   DCHECK(waiting_read_);
   DWORD num_bytes, flags;
   BOOL ok = WSAGetOverlappedResult(socket_, &core_->read_overlapped_,
                                    &num_bytes, FALSE, &flags);
   WSAResetEvent(core_->read_overlapped_.hEvent);
   waiting_read_ = false;
   core_->read_iobuffer_ = NULL;
   if (ok) {
     base::StatsCounter read_bytes("tcp.read_bytes");
     read_bytes.Add(num_bytes);
+    num_bytes_read_ += num_bytes;
     if (num_bytes > 0)
       use_history_.set_was_used_to_convey_data();
     net_log_.AddByteTransferEvent(NetLog::TYPE_SOCKET_BYTES_RECEIVED,
                                   num_bytes, core_->read_buffer_.buf);
   }
   DoReadCallback(ok ? num_bytes : MapSystemError(WSAGetLastError()));
 }
 
 void TCPClientSocketWin::DidCompleteWrite() {
   DCHECK(waiting_write_);
@@ skipping 22 matching lines @@
         use_history_.set_was_used_to_convey_data();
       net_log_.AddByteTransferEvent(NetLog::TYPE_SOCKET_BYTES_SENT, num_bytes,
                                     core_->write_buffer_.buf);
     }
   }
   core_->write_iobuffer_ = NULL;
   DoWriteCallback(rv);
 }
 
 }  // namespace net