Enable spare RenderProcessHost to be preinitialized.

content/browser/renderer_host/render_process_host_impl.cc

 // Copyright 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.
 
 // Represents the browser side of the browser <--> renderer communication
 // channel. There will be one RenderProcessHost per renderer process.
 
 #include "content/browser/renderer_host/render_process_host_impl.h"
 
 #include <algorithm>
@@ skipping 447 matching lines @@
 
  private:
   std::unique_ptr<std::map<int, SessionStorageNamespaceMap>>
       session_storage_namespaces_awaiting_close_;
   DISALLOW_COPY_AND_ASSIGN(SessionStorageHolder);
 };
 
 const void* const kDefaultSubframeProcessHostHolderKey =
     &kDefaultSubframeProcessHostHolderKey;
 
+// This class manages spare renderers.
+class SpareRenderProcessHostManager {
+ public:
+  SpareRenderProcessHostManager() {}
+
+  void StartSpareRenderProcessHost(BrowserContext* browser_context) {
+    StoragePartitionImpl* current_partition =
+        static_cast<StoragePartitionImpl*>(
+            BrowserContext::GetStoragePartition(browser_context, nullptr));
+
+    if (spare_render_process_host_ &&
+        matching_browser_context_ == browser_context &&
+        matching_storage_partition_ == current_partition) {
+      return;  // Nothing to warm up.
+    }
+
+    matching_browser_context_ = browser_context;
+    matching_storage_partition_ = current_partition;
+    spare_render_process_host_ = RenderProcessHostImpl::CreateRenderProcessHost(

[Benoit L, 2017/06/09 14:35:22]

Wouldn't this leak the previous one in the case where spare_render_process_host_
was not null above?

Actually, shouldn't it be a unique_ptr?

[mattcary, 2017/06/09 14:40:53]

I don't think so. RPH seem to handle their own deletion; see the destructor:
https://cs.chromium.org/chromium/src/content/browser/renderer_host/render_pro...

There appears to be a global host list. Probably it can't be deleted arbitrarily
as it needs to wait for cleanup IPCs from the renderer process?

And indeed, in browsertests that assertion does fire (browsertests are
complicated by other reasons and not included here).

There may be something I'm not understanding, though, so any insight you have
would be appreciated...

+        browser_context, current_partition, false /* is_for_guests_only */);
+    spare_render_process_host_->Init();
+  }
+
+  RenderProcessHost* MaybeTakeSpareRenderProcessHost(
+      const BrowserContext* browser_context,
+      const StoragePartition* partition,
+      bool is_for_guests_only) {
+    if (!spare_render_process_host_ ||
+        browser_context != matching_browser_context_ ||
+        partition != matching_storage_partition_ || is_for_guests_only) {
+      // As a new RenderProcessHost will almost certainly be created, we delete
+      // the non-matching one so as not to waste resources.
+      // TODO(mattcary): is deleting the RPH enough?
+      CleanupSpareRenderProcessHost();
+      return nullptr;
+    }
+    RenderProcessHost* rph = spare_render_process_host_;
+    spare_render_process_host_ = nullptr;
+    return rph;
+  }
+
+  void CleanupSpareRenderProcessHost() {
+    if (spare_render_process_host_) {
+      spare_render_process_host_->Cleanup();
+      spare_render_process_host_ = nullptr;
+    }
+  }
+
+ private:
+  RenderProcessHost* spare_render_process_host_;
+
+  // Used only to check if a creation request matches the
+  // spare, and not accessed.
+  const BrowserContext* matching_browser_context_ = nullptr;
+  const StoragePartition* matching_storage_partition_ = nullptr;
+
+  DISALLOW_COPY_AND_ASSIGN(SpareRenderProcessHostManager);
+};
+
+SpareRenderProcessHostManager* g_spare_render_process_host_manager = nullptr;
+
 class DefaultSubframeProcessHostHolder : public base::SupportsUserData::Data,
                                          public RenderProcessHostObserver {
  public:
   explicit DefaultSubframeProcessHostHolder(BrowserContext* browser_context)
       : browser_context_(browser_context) {}
   ~DefaultSubframeProcessHostHolder() override {}
 
   // Gets the correct render process to use for this SiteInstance.
   RenderProcessHost* GetProcessHost(SiteInstance* site_instance,
                                     bool is_for_guests_only) {
     StoragePartition* default_partition =
         BrowserContext::GetDefaultStoragePartition(browser_context_);
     StoragePartition* partition =
         BrowserContext::GetStoragePartition(browser_context_, site_instance);
 
     // Is this the default storage partition? If it isn't, then just give it its
     // own non-shared process.
     if (partition != default_partition || is_for_guests_only) {
-      RenderProcessHostImpl* host = new RenderProcessHostImpl(
+      RenderProcessHost* host = RenderProcessHostImpl::CreateRenderProcessHost(
           browser_context_, static_cast<StoragePartitionImpl*>(partition),
           is_for_guests_only);
       host->SetIsNeverSuitableForReuse();
       return host;
     }
 
     // If we already have a shared host for the default storage partition, use
     // it.
     if (host_)
       return host_;
 
-    host_ = new RenderProcessHostImpl(
+    if (g_spare_render_process_host_manager) {
+      host_ =
+          g_spare_render_process_host_manager->MaybeTakeSpareRenderProcessHost(
+              browser_context_, partition, false /* is for guests only */);
+    }
+
+    host_ = RenderProcessHostImpl::CreateRenderProcessHost(
         browser_context_, static_cast<StoragePartitionImpl*>(partition),
         false /* for guests only */);
     host_->SetIsNeverSuitableForReuse();
     host_->AddObserver(this);
 
     return host_;
   }
 
   // Implementation of RenderProcessHostObserver.
   void RenderProcessHostDestroyed(RenderProcessHost* host) override {
     DCHECK_EQ(host_, host);
     host_->RemoveObserver(this);
     host_ = nullptr;
   }
 
  private:
   BrowserContext* browser_context_;
 
   // The default subframe render process used for the default storage partition
   // of this BrowserContext.
-  RenderProcessHostImpl* host_ = nullptr;
+  RenderProcessHost* host_ = nullptr;
 };
 
 void CreateMemoryCoordinatorHandle(
     int render_process_id,
     const service_manager::BindSourceInfo& source_info,
     mojom::MemoryCoordinatorHandleRequest request) {
   MemoryCoordinatorImpl::GetInstance()->CreateHandle(render_process_id,
                                                      std::move(request));
 }
 
@@ skipping 370 matching lines @@
     max_count = std::min(max_count, kMaxRendererProcessCount);
   }
   return max_count;
 }
 
 // static
 void RenderProcessHost::SetMaxRendererProcessCount(size_t count) {
   g_max_renderer_count_override = count;
 }
 
+// static
+RenderProcessHost* RenderProcessHostImpl::CreateRenderProcessHost(
+    BrowserContext* browser_context,
+    StoragePartitionImpl* storage_partition_impl,
+    bool is_for_guests_only) {
+  if (g_render_process_host_factory_) {
+    return g_render_process_host_factory_->CreateRenderProcessHost(
+        browser_context);
+  }
+
+  return new RenderProcessHostImpl(browser_context, storage_partition_impl,
+                                   is_for_guests_only);
+}
+
 RenderProcessHostImpl::RenderProcessHostImpl(
     BrowserContext* browser_context,
     StoragePartitionImpl* storage_partition_impl,
     bool is_for_guests_only)
     : fast_shutdown_started_(false),
       deleting_soon_(false),
 #ifndef NDEBUG
       is_self_deleted_(false),
 #endif
       pending_views_(0),
@@ skipping 1988 matching lines @@
           host->GetID()) !=
       WebUIControllerFactoryRegistry::GetInstance()->UseWebUIBindingsForURL(
           browser_context, site_url)) {
     return false;
   }
 
   return GetContentClient()->browser()->IsSuitableHost(host, site_url);
 }
 
 // static
+void RenderProcessHost::StartSpareRenderProcessHost(
+    content::BrowserContext* browser_context) {
+  if (!g_spare_render_process_host_manager) {

[Benoit L, 2017/06/09 14:35:22]

since this is a leaky singleton, what about a LazyInstance?
We don't need it to be threadsafe though...

[mattcary, 2017/06/09 14:40:53]

Done

+    g_spare_render_process_host_manager = new SpareRenderProcessHostManager();
+  }
+  g_spare_render_process_host_manager->StartSpareRenderProcessHost(
+      browser_context);
+}
+
+// static
 bool RenderProcessHost::run_renderer_in_process() {
   return g_run_renderer_in_process_;
 }
 
 // static
 void RenderProcessHost::SetRunRendererInProcess(bool value) {
   g_run_renderer_in_process_ = value;
 
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
   if (value) {
@@ skipping 175 matching lines @@
     default:
       break;
   }
 
   // If not (or if none found), see if we should reuse an existing process.
   if (!render_process_host &&
       ShouldTryToUseExistingProcessHost(browser_context, site_url)) {
     render_process_host = GetExistingProcessHost(browser_context, site_url);
   }
 
+  // Try to use a spare process if one is found.
+  StoragePartitionImpl* partition = static_cast<StoragePartitionImpl*>(
+      BrowserContext::GetStoragePartition(browser_context, site_instance));
+  if (!render_process_host && g_spare_render_process_host_manager) {
+    render_process_host =
+        g_spare_render_process_host_manager->MaybeTakeSpareRenderProcessHost(
+            browser_context, partition, is_for_guests_only);
+  }
+
   // Otherwise (or if that fails), create a new one.
   if (!render_process_host) {
-    if (g_render_process_host_factory_) {
-      render_process_host =
-          g_render_process_host_factory_->CreateRenderProcessHost(
-              browser_context, site_instance);
-    } else {
-      StoragePartitionImpl* partition = static_cast<StoragePartitionImpl*>(
-          BrowserContext::GetStoragePartition(browser_context, site_instance));
-      render_process_host = new RenderProcessHostImpl(
-          browser_context, partition, is_for_guests_only);
-    }
+    render_process_host =
+        CreateRenderProcessHost(browser_context, partition, is_for_guests_only);

[Benoit L, 2017/06/09 14:35:22]

Doesn't this bypass the factory?

[mattcary, 2017/06/09 14:40:53]

Nope, that's exactly why I added CreateRenderProcessHost.

   }
   return render_process_host;
 }
 
 void RenderProcessHostImpl::CreateSharedRendererHistogramAllocator() {
   // Create a persistent memory segment for renderer histograms only if
   // they're active in the browser.
   if (!base::GlobalHistogramAllocator::Get())
     return;
 
@@ skipping 486 matching lines @@
   LOG(ERROR) << "Terminating render process for bad Mojo message: " << error;
 
   // The ReceivedBadMessage call below will trigger a DumpWithoutCrashing.
   // Capture the error message in a crash key value.
   base::debug::ScopedCrashKey error_key_value("mojo-message-error", error);
   bad_message::ReceivedBadMessage(render_process_id,
                                   bad_message::RPH_MOJO_PROCESS_ERROR);
 }
 
 }  // namespace content