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

net/socket/client_socket_pool_base.cc

Index: net/socket/client_socket_pool_base.cc
===================================================================
--- net/socket/client_socket_pool_base.cc	(revision 90003)
+++ net/socket/client_socket_pool_base.cc	(working copy)
@@ -4,11 +4,15 @@
 
 #include "net/socket/client_socket_pool_base.h"
 
+#include <math.h>
+#include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/format_macros.h"
+#include "base/logging.h"
 #include "base/message_loop.h"
 #include "base/metrics/stats_counters.h"
 #include "base/stl_util-inl.h"
+#include "base/string_number_conversions.h"
 #include "base/string_util.h"
 #include "base/time.h"
 #include "base/values.h"
@@ -32,10 +36,33 @@
 // after a certain timeout has passed without receiving an ACK.
 bool g_connect_backup_jobs_enabled = true;
 
+double g_socket_reuse_policy_penalty_exponent = -1;

[M-A Ruel, 2011/06/22 14:53:33]

!!!!!

Do not use global variable there. There was not thread safe.

[gagansingh, 2011/06/23 15:53:59]

There were lot of review comments on this one, this is what willchan and mbelshe
finally settled on (see http://codereview.chromium.org/6990036/ for more review
comments).

+int g_socket_reuse_policy = -1;
+
 }  // namespace
 
 namespace net {
 
+int GetSocketReusePolicy() {
+  return g_socket_reuse_policy;
+}
+
+void SetSocketReusePolicy(int policy) {
+  DCHECK_GE(policy, 0);
+  DCHECK_LE(policy, 2);
+  if (policy > 2 || policy < 0) {
+    LOG(ERROR) << "Invalid socket reuse policy";
+    return;
+  }
+
+  double exponents[] = { 0, 0.25, -1 };
+  g_socket_reuse_policy_penalty_exponent = exponents[policy];
+  g_socket_reuse_policy = policy;
+
+  DLOG(INFO) << "Setting g_socket_reuse_policy_penalty_exponent = "
+             << g_socket_reuse_policy_penalty_exponent;
+}
+
 ConnectJob::ConnectJob(const std::string& group_name,
                        base::TimeDelta timeout_duration,
                        Delegate* delegate,
@@ -363,6 +390,7 @@
     const Request* request, Group* group) {
   std::list<IdleSocket>* idle_sockets = group->mutable_idle_sockets();
   std::list<IdleSocket>::iterator idle_socket_it = idle_sockets->end();
+  double max_score = -1;
 
   // Iterate through the idle sockets forwards (oldest to newest)
   //   * Delete any disconnected ones.
@@ -379,7 +407,22 @@
 
     if (it->socket->WasEverUsed()) {
       // We found one we can reuse!
-      idle_socket_it = it;
+      double score = 0;
+      int64 bytes_read = it->socket->NumBytesRead();
+      double num_kb = static_cast<double>(bytes_read) / 1024.0;
+      int idle_time_sec = (base::TimeTicks::Now() - it->start_time).InSeconds();
+      idle_time_sec = std::max(1, idle_time_sec);
+
+      if (g_socket_reuse_policy_penalty_exponent >= 0 && num_kb >= 0) {
+        score = num_kb / pow(idle_time_sec,
+                             g_socket_reuse_policy_penalty_exponent);
+      }
+
+      // Equality to prefer recently used connection.
+      if (score >= max_score) {
+        idle_socket_it = it;
+        max_score = score;
+      }
     }
 
     ++it;