Don't poll the PAC script during periods of network inactivity.

net/proxy/proxy_service.h

 // 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.
 
 #ifndef NET_PROXY_PROXY_SERVICE_H_
 #define NET_PROXY_PROXY_SERVICE_H_
 #pragma once
 
 #include <string>
 #include <vector>
@@ skipping 25 matching lines @@
 class ProxyScriptDecider;
 class ProxyScriptFetcher;
 
 // This class can be used to resolve the proxy server to use when loading a
 // HTTP(S) URL.  It uses the given ProxyResolver to handle the actual proxy
 // resolution.  See ProxyResolverV8 for example.
 class NET_EXPORT ProxyService : public NetworkChangeNotifier::IPAddressObserver,
                                 public ProxyConfigService::Observer,
                                 NON_EXPORTED_BASE(public base::NonThreadSafe) {
  public:
-  // Only used by unit-tests.
-  enum PollPolicy {
-    POLL_POLICY_REGULAR,  // Normal PAC poll policy (retry periodically).
-    POLL_POLICY_NEVER,  // Don't re-fetch PAC scripts for changes.
-    POLL_POLICY_IMMEDIATE,  // Check every 1 ms.
+  // This interface defines the set of policies for when to poll the PAC
+  // script for changes.
+  //
+  // The polling policy decides what the next poll delay should be in
+  // milliseconds. It also decides how to wait for this delay -- either
+  // by starting a timer to do the poll at exactly |next_delay_ms|
+  // (MODE_USE_TIMER) or by waiting for the first network request issued after
+  // |next_delay_ms| (MODE_START_AFTER_ACTIVITY).
+  //
+  // The timer method is more precise and guarantees that polling happens when
+  // it was requested. However it has the disadvantage of causing spurious CPU
+  // and network activity. It is a reasonable choice to use for short poll
+  // intervals which only happen a couple times.
+  //
+  // However for repeated timers this will prevent the browser from going
+  // idle. MODE_START_AFTER_ACTIVITY solves this problem by only polling in
+  // direct response to network activity. The drawback to
+  // MODE_START_AFTER_ACTIVITY is since the poll is initiated only after the
+  // request is received, the first couple requests initiated after a long
+  // period of inactivity will likely see

[wtc, 2012/01/13 01:08:45]

Nit: this line is too short.

[eroman, 2012/01/13 20:05:27]

Done.

+  // a stale version of the PAC script until the background polling gets a
+  // chance to update things.
+  class NET_EXPORT_PRIVATE PacPollPolicy {
+   public:
+    enum Mode {
+      MODE_USE_TIMER,
+      MODE_START_AFTER_ACTIVITY,
+    };
+
+    virtual ~PacPollPolicy();
+    virtual Mode GetInitialDelay(int error, int64* next_delay_ms) const = 0;
+    virtual Mode GetNextDelay(int64 current_delay_ms,
+                              int64* next_delay_ms) const = 0;

[wtc, 2012/01/13 01:08:45]

You didn't document these two methods.

[eroman, 2012/01/13 20:05:27]

Done.

   };
 
   // The instance takes ownership of |config_service| and |resolver|.
   // |net_log| is a possibly NULL destination to send log events to. It must
   // remain alive for the lifetime of this ProxyService.
   ProxyService(ProxyConfigService* config_service,
                ProxyResolver* resolver,
                NetLog* net_log);
 
   virtual ~ProxyService();
@@ skipping 178 matching lines @@
   static ProxyConfigService* CreateSystemProxyConfigService(
       MessageLoop* io_loop, MessageLoop* file_loop);
 
   // This method should only be used by unit tests.
   void set_stall_proxy_auto_config_delay(base::TimeDelta delay) {
     stall_proxy_auto_config_delay_ = delay;
   }
 
   // This method should only be used by unit tests. Returns the previously
   // active policy.
-  static PollPolicy set_pac_script_poll_policy(PollPolicy policy);
+  static const PacPollPolicy* set_pac_script_poll_policy(
+      const PacPollPolicy* policy);
+
+  // This method should only be used by unit tests. Creates an instance
+  // of the default internal PacPollPolicy used by ProxyService.
+  static scoped_ptr<PacPollPolicy> CreateDefaultPacPollPolicy();
 
  private:
   FRIEND_TEST_ALL_PREFIXES(ProxyServiceTest, UpdateConfigAfterFailedAutodetect);
   FRIEND_TEST_ALL_PREFIXES(ProxyServiceTest, UpdateConfigFromPACToDirect);
   friend class PacRequest;
   class InitProxyResolver;
   class ProxyScriptDeciderPoller;
 
   // TODO(eroman): change this to a std::set. Note that this requires updating
   // some tests in proxy_service_unittest.cc such as:
@@ skipping 159 matching lines @@
 
   base::WaitableEvent event_;
   CompletionCallback callback_;
   ProxyInfo proxy_info_;
   int result_;
 };
 
 }  // namespace net
 
 #endif  // NET_PROXY_PROXY_SERVICE_H_