Shut down proxy resolver utility processes when no longer needed.

chrome/browser/net/utility_process_mojo_proxy_resolver_factory.cc

 // Copyright 2015 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.
 
 #include "chrome/browser/net/utility_process_mojo_proxy_resolver_factory.h"
 
 #include "base/logging.h"
 #include "base/memory/singleton.h"
 #include "chrome/grit/generated_resources.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/utility_process_host.h"
 #include "content/public/browser/utility_process_host_client.h"
 #include "content/public/common/service_registry.h"
 #include "net/proxy/mojo_proxy_resolver_factory.h"
 #include "ui/base/l10n/l10n_util.h"
 
+namespace {
+const int kUtilityProcessIdleTimeoutSeconds = 5;
+}
+
 // static
 UtilityProcessMojoProxyResolverFactory*
 UtilityProcessMojoProxyResolverFactory::GetInstance() {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
   return Singleton<
       UtilityProcessMojoProxyResolverFactory,
       LeakySingletonTraits<UtilityProcessMojoProxyResolverFactory>>::get();
 }
 
 UtilityProcessMojoProxyResolverFactory::
@@ skipping 13 matching lines @@
           scoped_refptr<content::UtilityProcessHostClient>(),
           base::MessageLoopProxy::current().get());
   utility_process_host->SetName(l10n_util::GetStringUTF16(
       IDS_UTILITY_PROCESS_PROXY_RESOLVER_NAME));
   bool process_started = utility_process_host->StartMojoMode();
   if (process_started) {
     content::ServiceRegistry* service_registry =
         utility_process_host->GetServiceRegistry();
     service_registry->ConnectToRemoteService(&resolver_factory_);
     resolver_factory_.set_error_handler(this);
+    utility_process_host_ = utility_process_host->AsWeakPtr();
   } else {
     LOG(ERROR) << "Unable to connect to utility process";
   }
 }
 
-void UtilityProcessMojoProxyResolverFactory::Create(
+scoped_ptr<base::ScopedClosureRunner>
+UtilityProcessMojoProxyResolverFactory::Create(
     mojo::InterfaceRequest<net::interfaces::ProxyResolver> req,
     net::interfaces::HostResolverPtr host_resolver) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
   if (!resolver_factory_)
     CreateProcessAndConnect();
 
   if (!resolver_factory_) {
     // If there's still no factory, then utility process creation failed so
     // close |req|'s message pipe, which should cause a connection error.
     req = nullptr;
-    return;
+    return nullptr;
   }
+  idle_timer_.Stop();
+  num_proxy_resolvers_++;
   resolver_factory_->CreateResolver(req.Pass(), host_resolver.Pass());
+  return make_scoped_ptr(new base::ScopedClosureRunner(
+      base::Bind(&UtilityProcessMojoProxyResolverFactory::OnResolverDestroyed,
+                 base::Unretained(this))));

[eroman, 2015/04/15 00:46:44]

What makes the use of unretained safe here?

[Sam McNally, 2015/04/15 06:04:22]

UtilityProcessMojoProxyResolverFactory is singleton.

 }
 
 void UtilityProcessMojoProxyResolverFactory::OnConnectionError() {
   DVLOG(1) << "Disconnection from utility process detected";
   resolver_factory_.reset();
 }
+
+void UtilityProcessMojoProxyResolverFactory::OnResolverDestroyed() {
+  DCHECK_GT(num_proxy_resolvers_, 0u);
+  if (--num_proxy_resolvers_ == 0) {
+    // When all proxy resolvers have been destroyed, the proxy resolver utility
+    // process is no longer needed. However, new proxy resolvers may be created
+    // shortly after being destroyed (e.g. due to a network change). If the
+    // utility process is shut down immediately, this would cause unnecessary
+    // process churn, so wait for an idle timeout before shutting down the
+    // proxy resolver utility process.
+    idle_timer_.Start(
+        FROM_HERE,
+        base::TimeDelta::FromSeconds(kUtilityProcessIdleTimeoutSeconds), this,
+        &UtilityProcessMojoProxyResolverFactory::OnIdleTimeout);
+  }
+}
+
+void UtilityProcessMojoProxyResolverFactory::OnIdleTimeout() {
+  delete utility_process_host_.get();

[eroman, 2015/04/15 00:46:44]

Why is it written like this, rather than just a call to reset?

[Sam McNally, 2015/04/15 06:04:22]

utility_process_host_ is a WeakPtr.

+  utility_process_host_.reset();
+  resolver_factory_.reset();
+}