Enable spare RenderProcessHost to be preinitialized.

content/browser/renderer_host/render_process_host_browsertest.cc

Index: content/browser/renderer_host/render_process_host_browsertest.cc
diff --git a/content/browser/renderer_host/render_process_host_browsertest.cc b/content/browser/renderer_host/render_process_host_browsertest.cc
index 866e829d1b74c93dad22fc5b77ee71e84cf19598..c7ddc69020a14f82b5020e8f7e6040f655e9ce04 100644
--- a/content/browser/renderer_host/render_process_host_browsertest.cc
+++ b/content/browser/renderer_host/render_process_host_browsertest.cc
@@ -17,6 +17,10 @@
 #include "content/public/test/content_browser_test_utils.h"
 #include "content/public/test/test_service.mojom.h"
 #include "content/shell/browser/shell.h"
+#include "content/shell/browser/shell_browser_context.h"
+#include "content/shell/browser/shell_browser_main_parts.h"
+#include "content/shell/browser/shell_content_browser_client.h"
+#include "content/test/test_content_browser_client.h"
 #include "media/base/bind_to_current_loop.h"
 #include "media/base/media_switches.h"
 #include "media/base/test_data_util.h"
@@ -73,6 +77,20 @@ class RenderProcessHostTest : public ContentBrowserTest,
   base::Closure process_exit_callback_;
 };
 
+// A mock ContentBrowserClient that only considers a spare renderer to be a
+// suitable host.
+class SpareRendererContentBrowserClient : public TestContentBrowserClient {
+ public:
+  bool IsSuitableHost(RenderProcessHost* process_host,
+                      const GURL& site_url) override {
+    if (RenderProcessHostImpl::GetSpareRenderProcessHostForTesting()) {
+      return process_host ==
+             RenderProcessHostImpl::GetSpareRenderProcessHostForTesting();
+    }
+    return true;
+  }
+};
+
 // Sometimes the renderer process's ShutdownRequest (corresponding to the
 // ViewMsg_WasSwappedOut from a previous navigation) doesn't arrive until after
 // the browser process decides to re-use the renderer for a new purpose.  This
@@ -130,6 +148,113 @@ IN_PROC_BROWSER_TEST_F(RenderProcessHostTest,
   EXPECT_EQ(2, RenderProcessHostCount());
 }
 
+IN_PROC_BROWSER_TEST_F(RenderProcessHostTest, SpareRenderProcessHostTaken) {
+  ASSERT_TRUE(embedded_test_server()->Start());
+
+  RenderProcessHost::WarmupSpareRenderProcessHost(
+      ShellContentBrowserClient::Get()->browser_context());
+  RenderProcessHost* spare_renderer =
+      RenderProcessHostImpl::GetSpareRenderProcessHostForTesting();
+  EXPECT_NE(nullptr, spare_renderer);
+
+  GURL test_url = embedded_test_server()->GetURL("/simple_page.html");
+  Shell* window = CreateBrowser();
+  NavigateToURL(window, test_url);
+
+  EXPECT_EQ(spare_renderer,
+            window->web_contents()->GetMainFrame()->GetProcess());
+
+  // The spare render process host should no longer be available.
+  EXPECT_EQ(nullptr,
+            RenderProcessHostImpl::GetSpareRenderProcessHostForTesting());
+}
+
+IN_PROC_BROWSER_TEST_F(RenderProcessHostTest, SpareRenderProcessHostNotTaken) {
+  ASSERT_TRUE(embedded_test_server()->Start());
+
+  RenderProcessHost::WarmupSpareRenderProcessHost(
+      ShellContentBrowserClient::Get()->off_the_record_browser_context());
+  RenderProcessHost* spare_renderer =
+      RenderProcessHostImpl::GetSpareRenderProcessHostForTesting();
+  GURL test_url = embedded_test_server()->GetURL("/simple_page.html");
+  Shell* window = CreateBrowser();
+  NavigateToURL(window, test_url);
+
+  // There should have been another process created for the navigation.
+  EXPECT_NE(spare_renderer,
+            window->web_contents()->GetMainFrame()->GetProcess());
+
+  // The spare RenderProcessHost should have been cleaned up. Note this
+  // behavior is identical to what would have happened if the RenderProcessHost
+  // were taken.
+  EXPECT_EQ(nullptr,
+            RenderProcessHostImpl::GetSpareRenderProcessHostForTesting());
+}
+
+IN_PROC_BROWSER_TEST_F(RenderProcessHostTest, SpareRenderProcessHostKilled) {
+  RenderProcessHost::WarmupSpareRenderProcessHost(
+      ShellContentBrowserClient::Get()->browser_context());
+
+  RenderProcessHost* spare_renderer =
+      RenderProcessHostImpl::GetSpareRenderProcessHostForTesting();
+  mojom::TestServicePtr service;
+  ASSERT_NE(nullptr, spare_renderer);
+  BindInterface(spare_renderer, &service);
+
+  base::RunLoop run_loop;
+  set_process_exit_callback(run_loop.QuitClosure());
+  spare_renderer->AddObserver(this);  // For process_exit_callback.
+
+  // Should reply with a bad message and cause process death.
+  service->DoSomething(base::Bind(&base::DoNothing));
+  run_loop.Run();
+
+  // The spare RenderProcessHost should disappear when its process dies.
+  EXPECT_EQ(nullptr,
+            RenderProcessHostImpl::GetSpareRenderProcessHostForTesting());
+}
+
+// Test that the spare renderer works correctly when the limit on the maximum
+// number of processes is small.
+IN_PROC_BROWSER_TEST_F(RenderProcessHostTest,
+                       SpareRendererSurpressedMaxProcesses) {
+  ASSERT_TRUE(embedded_test_server()->Start());
+
+  SpareRendererContentBrowserClient browser_client;
+  ContentBrowserClient* old_client =
+      SetBrowserClientForTesting(&browser_client);
+
+  RenderProcessHost::SetMaxRendererProcessCount(1);
+
+  // A process is created with shell startup, so with a maximum of one renderer
+  // process the spare RPH should not be created.
+  RenderProcessHost::WarmupSpareRenderProcessHost(
+      ShellContentBrowserClient::Get()->browser_context());
+  EXPECT_EQ(nullptr,
+            RenderProcessHostImpl::GetSpareRenderProcessHostForTesting());
+
+  // A spare RPH should be created with a max of 2 renderer processes.
+  RenderProcessHost::SetMaxRendererProcessCount(2);
+  RenderProcessHost::WarmupSpareRenderProcessHost(
+      ShellContentBrowserClient::Get()->browser_context());
+  RenderProcessHost* spare_renderer =
+      RenderProcessHostImpl::GetSpareRenderProcessHostForTesting();
+  EXPECT_NE(nullptr, spare_renderer);
+
+  // Thanks to the injected SpareRendererContentBrowserClient and the limit on
+  // processes, the spare RPH will always be used via GetExistingProcessHost()
+  // rather than picked up via MaybeTakeSpareRenderProcessHost().
+  GURL test_url = embedded_test_server()->GetURL("/simple_page.html");
+  NavigateToURL(CreateBrowser(), test_url);
+  // The spare RPH should have been dropped during CreateBrowser();
+  EXPECT_EQ(nullptr,
+            RenderProcessHostImpl::GetSpareRenderProcessHostForTesting());

[Charlie Reis, 2017/06/30 21:42:16]

nit: Might be worth including a check that the new Shell returned from
CreateBrowser() now has a process equal to the previous |spare_renderer|, just
to document/confirm that's where it went.

[mattcary, 2017/07/03 08:03:02]

Done.

+
+  // Revert to the default process limit and original ContentBrowserClient.
+  RenderProcessHost::SetMaxRendererProcessCount(0);
+  SetBrowserClientForTesting(old_client);
+}
+
 class ShellCloser : public RenderProcessHostObserver {
  public:
   ShellCloser(Shell* shell, std::string* logging_string)