[mojo-edk] Add MojoWatch and MojoCancelWatch APIs

mojo/edk/system/watcher_set.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 MOJO_EDK_SYSTEM_WATCHER_SET_H_
+#define MOJO_EDK_SYSTEM_WATCHER_SET_H_
+
+#include <unordered_map>
+
+#include "base/callback.h"
+#include "mojo/edk/system/dispatcher.h"
+#include "mojo/edk/system/handle_signals_state.h"
+#include "mojo/public/c/system/types.h"
+
+namespace mojo {
+namespace edk {
+
+// A WatcherSet maintains a set of callbacks to be notified in the event of
+// handle state changes. Note that callbacks are never run directly but are
+// instead attached as finalizers on a RequestContext. This ensures that the
+// callbacks can safely reenter the EDK.
+class WatcherSet {
+ public:
+  WatcherSet();
+  ~WatcherSet();
+
+  // Notifies any stored watchers of a state change if they're watching for some
+  // signals that are now satisfied or permanently unsatisfiable. Any
+  // notifications to dispatch are added to |request_context|'s list of
+  // finalizers to ensure that callbacks can safely re-enter the EDK.
+  void NotifyOfStateChange(const HandleSignalsState& state,
+                           Dispatcher::RequestContext* request_context);
+
+  // Cancels and removes all watchers. All removed watchers will have their
+  // callbacks invoked on |request_context| finalization to notify the watcher
+  // of cancellation.
+  void CancelAll(Dispatcher::RequestContext* request_context);
+
+  // Adds a new watcher to watch for signals in |signals| to be satisfied or
+  // unsatisfiable. |current_state| is the current signals state of the
+  // handle being watched.
+  //
+  // If the handle currently satisfies any signals in |signals|, the callback
+  // will be invoked on |request_context| finalization.
+  MojoResult Add(MojoHandleSignals signals,
+                 const Dispatcher::WatchCallback& callback,
+                 uintptr_t context,
+                 const HandleSignalsState& current_state,
+                 Dispatcher::RequestContext* request_context);
+
+  MojoResult Remove(uintptr_t context);
+
+ private:
+  struct Watcher {
+    Watcher(MojoHandleSignals signals,
+            const Dispatcher::WatchCallback& callback);
+    ~Watcher();
+
+    MojoHandleSignals signals;
+    Dispatcher::WatchCallback callback;
+  };
+
+  // If |current_state| satisfies signals in which |watcher| is interested, a
+  // finalizer is added to |request_context| which invokes the watcher's
+  // callback.
+  void MaybeNotifyWatcher(const Watcher& watcher,
+                          const MojoHandleSignalsState& current_state,
+                          Dispatcher::RequestContext* request_context);
+
+  // A map of watchers keyed on context value.
+  std::unordered_map<uintptr_t, Watcher> watchers_;
+
+  DISALLOW_COPY_AND_ASSIGN(WatcherSet);
+};
+
+}  // namespace edk
+}  // namespace mojo
+
+#endif  // MOJO_EDK_SYSTEM_WATCHER_SET_H_