[Win] Create ModuleWatcher.

chrome/common/conflicts/module_watcher_win.h

+// Copyright 2016 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 CHROME_COMMON_CONFLICTS_MODULE_WATCHER_WIN_H_
+#define CHROME_COMMON_CONFLICTS_MODULE_WATCHER_WIN_H_
+
+#include <memory>
+
+#include "base/callback.h"
+#include "chrome/common/conflicts/module_event_win.mojom.h"
+
+class ModuleWatcherTest;
+
+union LDR_DLL_NOTIFICATION_DATA;
+
+// This class observes modules as they are loaded and unloaded into a process's
+// address space.
+//
+// This class is safe to be created on any thread. Similarly, it is safe to be
+// destroyed on any thread, independent of the thread on which the instance was
+// created.
+class ModuleWatcher {
+ public:
+  // The type of callback that will be invoked for each module event. This is
+  // invoked by the loader and potentially on any thread. The loader lock is not
+  // held but the execution of this callback blocks the module from being bound.
+  // Keep the amount of work performed here to an absolute minimum. Note that
+  // it is possible for this callback to be invoked after the destruction of the
+  // watcher, but very unlikely.

[grt (UTC plus 2), 2016/11/15 10:35:34]

what makes it unlikely? is it any less likely than any other race (aren't they
all unlikely :-) )? do i misunderstand that any thread loading a module
concurrently with destruction will race with the unregistration in the dtor?

+  using OnModuleEventCallback =
+      base::Callback<void(const mojom::ModuleEvent& event)>;
+
+  // Creates and starts a watcher. This enumerates all loaded modules
+  // synchronously on the current thread during construction, and provides
+  // synchronous notifications as modules are loaded and unloaded. The callback
+  // is invoked in the context of the thread that is loading a module, and as
+  // such may be invoked on any thread in the process. Note that it is possible
+  // to receive two notifications for some modules as the initial loaded module
+  // enumeration races briefly with the callback mechanism. In this case both a
+  // MODULE_LOADED and a MODULE_ALREADY_LOADED event will be received for the
+  // same module. Since the callback is installed first no modules can be
+  // missed, however. This factory function may be called on any thread.
+  //
+  // Only a single instance of a watcher may exist at any moment. This will
+  // return nullptr when trying to create a second watcher.
+  static std::unique_ptr<ModuleWatcher> Create(
+      const OnModuleEventCallback& callback);
+
+  // This can be called on any thread. After destruction the |callback|
+  // provided to the constructor will no longer be invoked with module events.
+  ~ModuleWatcher();
+
+ protected:
+  // For unittesting.
+  friend class ModuleWatcherTest;
+
+  // Registers a DllNotification callback with the OS. Modifies
+  // |dll_notification_cookie_|. Can be called on any thread.
+  void RegisterDllNotificationCallback();
+
+  // Removes the installed DllNotification callback. Modifies
+  // |dll_notification_cookie_|. Can be called on any thread.
+  void UnregisterDllNotificationCallback();
+
+  // Enumerates all currently loaded modules, synchronously invoking callbacks
+  // on the current thread. Can be called on any thread.
+  void EnumerateAlreadyLoadedModules();
+
+  // Helper function for retrieving the callback associated with a given
+  // LdrNotification context.
+  static OnModuleEventCallback GetCallbackForContext(void* context);
+
+  // The loader notification callback. This is actually
+  // void CALLBACK LoaderNotificationCallback(
+  //     DWORD, const LDR_DLL_NOTIFICATION_DATA*, PVOID)
+  // Not using CALLBACK/DWORD/PVOID allows skipping the windows.h header from
+  // this file.
+  static void __stdcall LoaderNotificationCallback(
+      unsigned long notification_reason,
+      const LDR_DLL_NOTIFICATION_DATA* notification_data,
+      void* context);
+
+ private:
+  // Private to enforce Singleton semantics. See Create above.
+  explicit ModuleWatcher(const OnModuleEventCallback& callback);
+
+  // The current callback. Can end up being invoked on any thread.
+  OnModuleEventCallback callback_;
+  // Used by the DllNotification mechanism.
+  void* dll_notification_cookie_ = nullptr;
+
+  DISALLOW_COPY_AND_ASSIGN(ModuleWatcher);
+};
+
+#endif  // CHROME_COMMON_CONFLICTS_MODULE_WATCHER_WIN_H_