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

chrome/browser/browser_main.cc

Index: chrome/browser/browser_main.cc
===================================================================
--- chrome/browser/browser_main.cc	(revision 88319)
+++ chrome/browser/browser_main.cc	(working copy)
@@ -100,6 +100,7 @@
 #include "net/base/cookie_monster.h"
 #include "net/base/net_module.h"
 #include "net/base/network_change_notifier.h"
+#include "net/http/http_basic_stream.h"
 #include "net/http/http_network_layer.h"
 #include "net/http/http_stream_factory.h"
 #include "net/socket/client_socket_pool_base.h"
@@ -207,6 +208,9 @@
 #include "views/touchui/touch_factory.h"
 #endif
 
+using net::internal::ClientSocketPoolBaseHelper;
+using net::HttpBasicStream;
+
 namespace net {
 class NetLog;
 }  // namespace net
@@ -474,6 +478,61 @@
   }
 }
 
+// If --socket-reuse-policy is not specified, run an A/B test for choosing the
+// warmest socket.
+void BrowserMainParts::WarmConnectionFieldTrial() {
+  const CommandLine& command_line = parsed_command_line();
+  if (command_line.HasSwitch(switches::kSocketReusePolicy)) {
+    std::string alpha_str = command_line.GetSwitchValueASCII(
+        switches::kSocketReusePolicy);
+    int coef = -1;
+    base::StringToInt(alpha_str, &coef);
+
+    const int socket_policy[] = { 0, 1, 2 };
+    LOG(ERROR) << "Chose socket_reuse_policy coef = " << coef;
+    ApplySocketReuseGroup(coef, socket_policy, arraysize(socket_policy));
+    return;
+  }
+
+  const base::FieldTrial::Probability kWarmSocketDivisor = 100;
+  const base::FieldTrial::Probability kWarmSocketProbability = 33;
+
+  // After January 30, 2013 builds, it will always be in default group.
+  scoped_refptr<base::FieldTrial> warmest_socket_trial(
+      new base::FieldTrial(
+          "WarmSocketImpact", kWarmSocketDivisor, "last_accessed_socket",
+          2013, 1, 30));
+
+  // Default value is USE_LAST_ACCESSED_SOCKET.
+  const int last_accessed_socket = warmest_socket_trial->kDefaultGroupNumber;
+  const int warmest_socket = warmest_socket_trial->AppendGroup(
+      "warmest_socket", kWarmSocketProbability);
+  const int warm_socket = warmest_socket_trial->AppendGroup(
+      "warm_socket", kWarmSocketProbability);

[Mike Belshe, 2011/06/12 22:10:35]

nit:  you're now assuming that the field trial returns ints 0, 1, and 2.  ok.

[Gagan, 2011/06/13 03:52:47]

Actually no.
Im assuming that all 3 groups are represented by different numbers. The array
below will find the chosen experiment group in these numbers and use the match
index.
So the array constructed here is
a[0] = warmest socket
a[1] = warm
a[2] = last accessed
which is in sync with the enum.

+
+  const int warmest_socket_trial_group = warmest_socket_trial->group();
+
+  const int socket_policy[] = { warmest_socket, warm_socket,
+                                last_accessed_socket };
+  ApplySocketReuseGroup(warmest_socket_trial_group, socket_policy,
+                        arraysize(socket_policy));
+}
+
+void BrowserMainParts::ApplySocketReuseGroup(int warmest_socket_trial_group,
+                                             const int socket_policy[],
+                                             int num_groups) {
+  for (int i = 0; i < num_groups; i++) {
+    if (warmest_socket_trial_group == socket_policy[i]) {
+      ClientSocketPoolBaseHelper::SetSocketReusePolicy(i);
+      HttpBasicStream::SetSocketReusePolicy(i);
+      return;
+    }
+  }
+
+  LOG(ERROR) << "Not a valid socket reuse policy group";
+  NOTREACHED() << "Not a valid socket reuse policy group";

[Mike Belshe, 2011/06/12 22:10:35]

nit:  the notreached() will crash even a release build, right?  so these two are
redundant?

[Gagan, 2011/06/13 03:52:47]

base/logging.h defines NOTREACHED as DCHECK(false)
I added the log(error) temporarily because i was playing with release builds and
wanted to see the message.

+}
+
 // If neither --enable-connect-backup-jobs or --disable-connect-backup-jobs is
 // specified, run an A/B test for automatically establishing backup TCP
 // connections when a certain timeout value is exceeded.
@@ -593,6 +652,7 @@
   prerender::ConfigurePrefetchAndPrerender(parsed_command_line());
   SpdyFieldTrial();
   ConnectBackupJobsFieldTrial();
+  WarmConnectionFieldTrial();
 }
 
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