Improve performance of proxy resolver by tracing DNS dependencies.

net/proxy/multi_threaded_proxy_resolver.h

 // Copyright (c) 2011 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_MULTI_THREADED_PROXY_RESOLVER_H_
 #define NET_PROXY_MULTI_THREADED_PROXY_RESOLVER_H_
 
 #include <deque>
 #include <vector>
 
@@ skipping 53 matching lines @@
 // (a) Scripts whose initialization has external dependencies on network or
 //     time may end up successfully initializing on some threads, but not
 //     others. So depending on what thread services the request, the result
 //     may jump between several possibilities.
 //
 // (b) Scripts whose FindProxyForURL() depends on side-effects may now
 //     work differently. For example, a PAC script which was incrementing
 //     a global counter and using that to make a decision. In the
 //     multi-threaded model, each thread may have a different value for this
 //     counter, so it won't globally be seen as monotonically increasing!
 class NET_EXPORT_PRIVATE MultiThreadedProxyResolver

[mmenke, 2013/01/18 19:59:40]

Not getting rid of this?

[eroman, 2013/01/23 03:26:02]

I would love to get rid of that, unfortunately there are other consumers of it
:(

The other guys are using it in conjunction with their system proxy resolver
service. I *could* theoretically just drop them into single-threaded mode, but I
would rather approach that with more caution later.

     : public ProxyResolver,
       NON_EXPORTED_BASE(public base::NonThreadSafe) {
  public:
   // Creates an asynchronous ProxyResolver that runs requests on up to
   // |max_num_threads|.
   //
   // For each thread that is created, an accompanying synchronous ProxyResolver
   // will be provisioned using |resolver_factory|. All methods on these
   // ProxyResolvers will be called on the one thread, with the exception of
   // ProxyResolver::Shutdown() which will be called from the origin thread
   // prior to destruction.
   //
   // The constructor takes ownership of |resolver_factory|.
   MultiThreadedProxyResolver(ProxyResolverFactory* resolver_factory,
                              size_t max_num_threads);
 
   virtual ~MultiThreadedProxyResolver();
 
   // ProxyResolver implementation:
   virtual int GetProxyForURL(const GURL& url,
                              ProxyInfo* results,
                              const CompletionCallback& callback,
                              RequestHandle* request,
                              const BoundNetLog& net_log) OVERRIDE;
   virtual void CancelRequest(RequestHandle request) OVERRIDE;
   virtual LoadState GetLoadState(RequestHandle request) const OVERRIDE;
-  virtual LoadState GetLoadStateThreadSafe(
-      RequestHandle request) const OVERRIDE;
   virtual void CancelSetPacScript() OVERRIDE;
   virtual void PurgeMemory() OVERRIDE;
   virtual int SetPacScript(
       const scoped_refptr<ProxyResolverScriptData>& script_data,
       const CompletionCallback& callback) OVERRIDE;
 
  private:
   class Executor;
   class Job;
   class SetPacScriptJob;
@@ skipping 23 matching lines @@
   const scoped_ptr<ProxyResolverFactory> resolver_factory_;
   const size_t max_num_threads_;
   PendingJobsQueue pending_jobs_;
   ExecutorList executors_;
   scoped_refptr<ProxyResolverScriptData> current_script_data_;
 };
 
 }  // namespace net
 
 #endif  // NET_PROXY_MULTI_THREADED_PROXY_RESOLVER_H_