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 88789)
+++ net/socket/client_socket_pool_base.cc	(working copy)
@@ -4,11 +4,16 @@
 
 #include "net/socket/client_socket_pool_base.h"
 
+#include <math.h>
+#include <utility>
+#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"
@@ -32,6 +37,9 @@
 // after a certain timeout has passed without receiving an ACK.
 bool g_connect_backup_jobs_enabled = true;
 
+// Decay coef.
+double g_socket_reuse_policy_penalty_coef = -1;
+
 }  // namespace
 
 namespace net {
@@ -363,7 +371,12 @@
     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;
+  std::pair<int, int64> best_pair, current_pair;
 
+  std::string debug_log(request->handle()->group_name());
+  double rtt_ms = 0;
+
   // Iterate through the idle sockets forwards (oldest to newest)
   //   * Delete any disconnected ones.
   //   * If we find a used idle socket, assign to |idle_socket|.  At the end,
@@ -379,11 +392,37 @@
 
     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_coef >= 0) {
+        score = num_kb / pow(idle_time_sec,
+                             g_socket_reuse_policy_penalty_coef);
+
+        debug_log = StringPrintf("%s\n%f\t%d\t%f", debug_log.data(),
+                                 num_kb, idle_time_sec, score);
+      }
+
+      // Equality to prefer recently used connection.
+      if (score >= max_score) {
+        idle_socket_it = it;
+        max_score = score;
+        best_pair = std::make_pair(bytes_read, idle_time_sec);
+        rtt_ms = it->socket->GetConnectTimeMicros();
+      }
     }
 
     ++it;
   }
+  debug_log = StringPrintf("%s\nChose socket <%d %ld>\nRtt = %f",
+                           debug_log.data(),
+                           best_pair.first, best_pair.second,
+                           rtt_ms);
+  LOG(ERROR) << "\n\n----------------------------------------" << debug_log;
 
   // If we haven't found an idle socket, that means there are no used idle
   // sockets.  Pick the oldest (first) idle socket (FIFO).
@@ -649,6 +688,20 @@
   return old_value;
 }
 
+// static
+double ClientSocketPoolBaseHelper::SetSocketReusePolicy(int policy) {
+  double old_value = g_socket_reuse_policy_penalty_coef;
+  g_socket_reuse_policy_penalty_coef =
+      policy == USE_WARMEST_SOCKET ? 0 :
+      (policy == USE_WARM_SOCKET ? 0.25 : -1);
+  DLOG(INFO) << "Setting g_socket_reuse_policy_penalty_coef = "
+             << g_socket_reuse_policy_penalty_coef;
+  // TODO(gagan): Remove this.
+  LOG(ERROR) << "Setting g_socket_reuse_policy_penalty_coef = "
+             << g_socket_reuse_policy_penalty_coef;
+  return old_value;
+}
+
 void ClientSocketPoolBaseHelper::EnableConnectBackupJobs() {
   connect_backup_jobs_enabled_ = g_connect_backup_jobs_enabled;
 }