Switch the TCP reads on Windows to use non-blocking/non-async I/O.

chrome/browser/chrome_browser_field_trials.cc

 // Copyright (c) 2012 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 "chrome/browser/chrome_browser_field_trials.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/metrics/field_trial.h"
@@ skipping 10 matching lines @@
 #include "chrome/browser/net/predictor.h"
 #include "chrome/browser/prerender/prerender_field_trial.h"
 #include "chrome/browser/safe_browsing/safe_browsing_blocking_page.h"
 #include "chrome/browser/ui/sync/one_click_signin_helper.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/chrome_version_info.h"
 #include "chrome/common/metrics/variations/variations_util.h"
 #include "net/http/http_stream_factory.h"
 #include "net/socket/client_socket_pool_base.h"
 #include "net/socket/client_socket_pool_manager.h"
+#include "net/socket/tcp_client_socket_win.h"
 #include "net/spdy/spdy_session.h"
 #include "net/spdy/spdy_session_pool.h"
 #include "ui/base/layout.h"
 
 #if defined(OS_WIN)
 #include "ui/base/win/dpi.h"  // For DisableNewTabFieldTrialIfNecesssary.
 #endif  // defined(OS_WIN)
 
 namespace {
 
@@ skipping 81 matching lines @@
   DefaultAppsFieldTrial();
   AutoLaunchChromeFieldTrial();
   gpu_util::InitializeCompositingFieldTrial();
   gpu_util::InitializeStage3DFieldTrial();
   SetupUniformityFieldTrials();
   AutocompleteFieldTrial::Activate();
   DisableNewTabFieldTrialIfNecesssary();
   SetUpSafeBrowsingInterstitialFieldTrial();
   SetUpInfiniteCacheFieldTrial();
   SetUpCacheSensitivityAnalysisFieldTrial();
+  WindowsOverlappedTCPReadsFieldTrial();
 #if defined(ENABLE_ONE_CLICK_SIGNIN)
   OneClickSigninHelper::InitializeFieldTrial();
 #endif
 }
 
 // This is an A/B test for the maximum number of persistent connections per
 // host. Currently Chrome, Firefox, and IE8 have this value set at 6. Safari
 // uses 4, and Fasterfox (a plugin for Firefox that supposedly configures it to
 // run faster) uses 8. We would like to see how much of an effect this value has
 // on browsing. Too large a value might cause us to run into SYN flood detection
@@ skipping 438 matching lines @@
                                                  2012, 12, 31, NULL));
   trial->AppendGroup("ControlA", sensitivity_analysis_probability);
   trial->AppendGroup("ControlB", sensitivity_analysis_probability);
   trial->AppendGroup("100A", sensitivity_analysis_probability);
   trial->AppendGroup("100B", sensitivity_analysis_probability);
   trial->AppendGroup("200A", sensitivity_analysis_probability);
   trial->AppendGroup("200B", sensitivity_analysis_probability);
   trial->AppendGroup("400A", sensitivity_analysis_probability);
   trial->AppendGroup("400B", sensitivity_analysis_probability);
 }
+
+void ChromeBrowserFieldTrials::WindowsOverlappedTCPReadsFieldTrial() {
+#if defined(OS_WIN)
+  if (parsed_command_line_.HasSwitch(switches::kOverlappedRead)) {
+    std::string option = parsed_command_line_.GetSwitchValueASCII(
+                                switches::kOverlappedRead);
+    if (LowerCaseEqualsASCII(option, "off")) {
+      net::TCPClientSocketWin::DisableOverlappedReads();
+    }
+  } else {
+    base::FieldTrial::Probability kNBREAD_DIVISOR = 2;  // 1 in 2 chance
+    base::FieldTrial::Probability kNBREAD_GROUP_PROBABILITY = 1;

[Ryan Sleevi, 2012/10/11 18:53:16]

Because these are not declared const, please do not use kConstantName naming (
http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Consta...
)

As shown in other field trials, simply use variable naming rules (or declare
these as const, and use kDivisor / kOverlappedReadProbability )

+    scoped_refptr<base::FieldTrial> nbread_trial(
+        base::FieldTrialList::FactoryGetFieldTrial("NBReadImpact",
+                         kNBREAD_DIVISOR, "NBReadStandard", 2015, 1, 1, NULL));
+    int overlapped_reads_disabled_group =
+                          nbread_trial->AppendGroup("NBReadNonBlocking",

[Ryan Sleevi, 2012/10/11 18:53:16]

The names of these probability groups are non-intuitive (overly abbreviated).

+                                                    kNBREAD_GROUP_PROBABILITY);
+    int assigned_group = nbread_trial->group();
+    if (assigned_group == overlapped_reads_disabled_group) {
+      net::TCPClientSocketWin::DisableOverlappedReads();
+    }
+  }

[Ryan Sleevi, 2012/10/11 18:53:16]

nit: Please follow the C++ Guide for horizontal whitespace. 

http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Functi...

"Wrapped parameters have a 4 space indent"

Note that in Chromium, this logic follows for all line continuations (much like
the C++ guide requires it for initializer lists and elsewhere), so that would
include assignment

int foo =
    bar();

+#endif
+}
+