[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 "base/callback.h"
+#include "chrome/common/conflicts/module_event_win.mojom.h"
+
+class ModuleWatcherTest;
+
+// 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:
+  using OnModuleEventCallback =

[grt (UTC plus 2), 2016/11/10 08:52:13]

please add a doc comment explaining the restrictions on this. for example, if
the loader lock is held when the callback is invoked, the implementer needs to
know what they can and cannot do. in any case, consider documenting that the
implementer shouldn't do anything expensive since the callback is run
synchronously with the actual load event (if that is the case), so it will block
some thread trying to do some work.

[chrisha, 2016/11/14 16:06:45]

Done.

+      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 (under the
+  // loader's lock!), and as such may be invoked on any thread in the process.

[grt (UTC plus 2), 2016/11/10 08:52:12]

is it under the loader's lock? i thought your discovery in
https://codereview.chromium.org/2473783005/#msg16 was that it isn't.

in any case, don't assume that the reader knows the implications of "under the
loader's lock".

[chrisha, 2016/11/14 16:06:45]

Removed the loader lock discussion entirely, as per my earlier comments. I have
the long-term memory of a fruit fly.

+  // Note that it is possible to receive two modifications for some modules as

[grt (UTC plus 2), 2016/11/10 08:52:13]

modifications -> notifications?

[chrisha, 2016/11/14 16:06:45]

Done.

+  // 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. Returns true on success,
+  // false otherwise. Modifies |dll_notification_cookie_|. Can be called on any
+  // thread.
+  bool RegisterDllNotificationCallback();
+
+  // Removes the installed DllNotification callback. Returns true on success,
+  // false otherwise. Modifies |dll_notification_cookie_|. Can be called on any
+  // thread.
+  bool UnregisterDllNotificationCallback();
+
+  // Enumerates all currently loaded modules, synchonously invoking callbacks on
+  // the current thread. Returns true on success, false otherwise. Can be
+  // called on any thread.
+  bool EnumerateAlreadyLoadedModules();
+
+  // The loader notification callback.
+  static void __stdcall LoaderNotificationCallback(
+      uint32_t notification_reason,
+      const void* notification_data,

[grt (UTC plus 2), 2016/11/10 08:52:12]

can you forward-decl LDR_DLL_NOTIFICATION_DATA in this file so that you don't
needs the various casts for this?

[chrisha, 2016/11/14 16:06:45]

Done.

+      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_