Improve performance of proxy resolver by tracing DNS dependencies.

net/proxy/proxy_resolver_v8_tracing.h

+// Copyright (c) 2013 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_RESOLVER_V8_TRACING_H_
+#define NET_PROXY_PROXY_RESOLVER_V8_TRACING_H_
+
+#include <deque>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/threading/non_thread_safe.h"
+#include "net/base/net_export.h"
+#include "net/proxy/proxy_resolver.h"
+
+namespace base {
+class Thread;
+class MessageLoopProxy;
+}  // namespace base
+
+namespace net {
+
+class HostResolver;
+class NetLog;
+class ProxyResolverErrorObserver;
+class ProxyResolverV8;
+
+// ProxyResolverV8Tracing is a non-blocking ProxyResolver. It executes
+// ProxyResolverV8 on a single helper thread, and does some magic to avoid
+// blocking in DNS. For more details see the design document:
+// https://docs.google.com/a/google.com/document/d/16Ij5OcVnR3s0MH4Z5XkhI9VTPoMJdaBn9rKreAmGOdE/edit?pli=1
+class NET_EXPORT_PRIVATE ProxyResolverV8Tracing
+    : public ProxyResolver,
+      NON_EXPORTED_BASE(public base::NonThreadSafe) {
+ public:
+  // Constructs a ProxyResolver that will issue DNS requests through
+  // |host_resolver|, forward Javascript errors through |error_observer|, and
+  // log Javascript errors and alerts to |net_log|.
+  //
+  // Note that the constructor takes ownership of |error_observer|, whereas
+  // |host_resolver| and |net_log| are expected to outlive |this|.
+  ProxyResolverV8Tracing(HostResolver* host_resolver,
+                         ProxyResolverErrorObserver* error_observer,

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

May want to take this as a scoped_ptr, just to make the ownership a little more
explicit.

[eroman, 2013/01/25 22:11:39]

I gave this a try but didn't much care for the resulting code, so will stick
with raw pointers.

Here is the sort of problems I ran into.

// ----- Original code
MockErrorObserver* error_observer = new MockErrorObserver;
ProxyResolverV8Tracing resolver(&host_resolver, error_observer, &log);

// ----- Failed translation 1
scoped_ptr<MockErrorObserver> error_observer(new MockErrorObserver);
ProxyResolverV8Tracing resolver(&host_resolver, error_observer.Pass(), &log);

<=== The above doesn't work because scoped_ptr<MockErrorObserver> is not
convertible to scoped_ptr<ProxyResolverErrorObserver> (the interface type).

// ----- Failed translation 2
scoped_ptr<MockErrorObserver> error_observer(new MockErrorObserver);
ProxyResolverV8Tracing resolver(&host_resolver, error_observer.PassAs(), &log);

<=== The above doesn't work either because it can't infer the type of the
template parameter (not exactly sure why not).

// ----- "successful" translation
scoped_ptr<MockErrorObserver> error_observer(new MockErrorObserver);
ProxyResolverV8Tracing resolver(&host_resolver,
error_observer.PassAs<ProxyResolverErrorObserver>(), &log);

<=== EEEEEEEEW. No thanks.

[mmenke, 2013/01/29 20:19:08]

Yea, that is more than a little horrifyingly hideous.

+                         NetLog* net_log);
+
+  virtual ~ProxyResolverV8Tracing();
+
+  // 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 void CancelSetPacScript() OVERRIDE;
+  virtual void PurgeMemory() OVERRIDE;
+  virtual int SetPacScript(
+      const scoped_refptr<ProxyResolverScriptData>& script_data,
+      const CompletionCallback& callback) OVERRIDE;
+
+ private:
+  class Job;
+  friend class Job;
+
+  scoped_ptr<base::Thread> thread_;
+  scoped_ptr<ProxyResolverV8> v8_resolver_;
+
+  HostResolver* host_resolver_;
+  scoped_ptr<ProxyResolverErrorObserver> error_observer_;
+  NetLog* net_log_;
+
+  scoped_refptr<Job> set_pac_script_job_;
+};
+
+}  // namespace net
+
+#endif  // NET_PROXY_PROXY_RESOLVER_V8_TRACING_H_