Teach EmbeddedWorkerInstance to create a process when it needs one.

content/browser/service_worker/service_worker_process_manager.h

+// Copyright 2014 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 CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_PROCESS_MANAGER_H_
+#define CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_PROCESS_MANAGER_H_
+
+#include <vector>
+
+#include "base/callback.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "content/common/service_worker/service_worker_status_code.h"
+
+class GURL;
+
+namespace content {
+
+class BrowserContext;
+class ServiceWorkerContextWrapper;
+
+// Interacts with the UI thread to keep RenderProcessHosts alive while the
+// ServiceWorker system is using them.  Each instance of
+// ServiceWorkerProcessManager is destroyed on the UI thread shortly after its
+// ServiceWorkerContextCore is destroyed on the IO thread.
+class CONTENT_EXPORT ServiceWorkerProcessManager {
+ public:
+  // |*this| must be owned by |context_wrapper|->context().

[michaeln, 2014/04/29 19:08:45]

Hmmm... does this create a reference cycle?

Wrapper owns Core owns Mgr refs Wrapper

[Jeffrey Yasskin, 2014/04/29 19:13:25]

Yes. The cycle is broken in Wrapper::Shutdown(). I forgot to add that comment
back in when I re-introduced the cycle.

We could also break the cycle by adding a WeakPtr to Wrapper. I don't think
there's a way to use just the WeakPtr to Core because we need to null out
browser_context_ when Shutdown() is called, before hopping threads.

+  explicit ServiceWorkerProcessManager(
+      ServiceWorkerContextWrapper* context_wrapper);
+
+  ~ServiceWorkerProcessManager();
+
+  // Returns a reference to a running process suitable for starting the Service
+  // Worker at |script_url|. Processes in |process_ids| will be checked in order
+  // for existence, and if none exist, then a new process will be created. Posts
+  // |callback| to the IO thread to indicate whether creation succeeded and the
+  // process ID that has a new reference.
+  //
+  // Allocation can fail with SERVICE_WORKER_ERROR_START_WORKER_FAILED if
+  // RenderProcessHost::Init fails.
+  void AllocateWorkerProcess(
+      const std::vector<int>& process_ids,
+      const GURL& script_url,
+      const base::Callback<void(ServiceWorkerStatusCode, int process_id)>&
+          callback) const;
+
+  // Drops a reference to a process that was running a Service Worker.  This
+  // must match a call to AllocateWorkerProcess.
+  void ReleaseWorkerProcess(int process_id);
+
+  // |increment_for_test| and |decrement_for_test| define how to look up a
+  // process by ID and increment or decrement its worker reference count. This
+  // must be called before any reference to this object escapes to another
+  // thread, and is considered part of construction.
+  void SetProcessRefcountOpsForTest(
+      const base::Callback<bool(int)>& increment_for_test,
+      const base::Callback<bool(int)>& decrement_for_test);
+
+ private:
+  bool IncrementWorkerRefcountByPid(int process_id) const;
+  bool DecrementWorkerRefcountByPid(int process_id) const;
+
+  // These fields are only accessed on the UI thread after construction.
+  scoped_refptr<ServiceWorkerContextWrapper> context_wrapper_;
+  base::Callback<bool(int)> increment_for_test_;
+  base::Callback<bool(int)> decrement_for_test_;
+
+  // Used to double-check that we don't access *this after it's destroyed.
+  base::WeakPtrFactory<ServiceWorkerProcessManager> weak_this_factory_;
+  base::WeakPtr<ServiceWorkerProcessManager> weak_this_;
+};
+
+}  // namespace content
+
+namespace base {
+// Specialized to post the deletion to the UI thread.
+template <>
+struct CONTENT_EXPORT DefaultDeleter<content::ServiceWorkerProcessManager> {
+  void operator()(content::ServiceWorkerProcessManager* ptr) const;
+};
+}  // namespace base
+
+#endif  // CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_PROCESS_MANAGER_H_