Mojo: Armed Watchers

mojo/edk/system/watcher_dispatcher.h

Index: mojo/edk/system/watcher_dispatcher.h
diff --git a/mojo/edk/system/watcher_dispatcher.h b/mojo/edk/system/watcher_dispatcher.h
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+// Copyright 2017 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_DISPATCHER_H_
+#define MOJO_EDK_SYSTEM_WATCHER_DISPATCHER_H_
+
+#include <map>
+#include <set>
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/synchronization/lock.h"
+#include "mojo/edk/system/dispatcher.h"
+#include "mojo/edk/system/handle_signals_state.h"
+#include "mojo/edk/system/system_impl_export.h"
+#include "mojo/public/c/system/watcher.h"
+
+namespace mojo {
+namespace edk {
+
+class Watch;
+
+// The dispatcher type which backs watcher handles.
+class WatcherDispatcher : public Dispatcher {
+ public:
+  // Constructs a new WatcherDispatcher which invokes |callback| when a
+  // registered watch observes some relevant state change.
+  explicit WatcherDispatcher(MojoWatcherCallback callback);
+
+  // Methods used by watched dispatchers to notify watchers of events.
+  void NotifyHandleState(Dispatcher* dispatcher,
+                         const HandleSignalsState& state);
+  void NotifyHandleClosed(Dispatcher* dispatcher);
+
+  // Method used by RequestContext (indirectly, via Watch) to complete
+  // notification operations from a safe stack frame to avoid reentrancy.
+  void InvokeWatchCallback(uintptr_t context,
+                           MojoResult result,
+                           const HandleSignalsState& state,
+                           MojoWatcherNotificationFlags flags);
+
+  // Dispatcher:
+  Type GetType() const override;
+  MojoResult Close() override;
+  MojoResult WatchDispatcher(scoped_refptr<Dispatcher> dispatcher,
+                             MojoHandleSignals signals,
+                             uintptr_t context) override;
+  MojoResult CancelWatch(uintptr_t context) override;
+  MojoResult Arm(uint32_t* num_ready_contexts,
+                 uintptr_t* ready_contexts,
+                 MojoResult* ready_results,
+                 MojoHandleSignalsState* ready_signals_states) override;
+
+ private:
+  class WatchedHandle;
+
+  friend class Watch;
+
+  ~WatcherDispatcher() override;
+
+  const MojoWatcherCallback callback_;
+
+  // Guards access to the fields below.
+  //
+  // NOTE: This may be acquired while holding another dispatcher's lock, as
+  // watched dispatchers call into WatcherDispatcher methods which lock this
+  // when issuing state change notifications. WatcherDispatcher must therefore
+  // take caution to NEVER acquire other dispatcher locks while this is held.
+  base::Lock lock_;
+
+  bool armed_ = false;
+  bool closed_ = false;
+
+  // Tracks all watched handle dispatchers.
+  std::map<Dispatcher*, std::unique_ptr<WatchedHandle>> watched_handles_;
+
+  // A mapping from context to Watch.
+  std::map<uintptr_t, scoped_refptr<Watch>> watches_;
+
+  // The set of all WatchedHandle elements from |watched_handles_| which are
+  // currently ready to signal. This is used for efficient arming behavior,
+  // as it allows for O(1) discovery of whether or not arming can succeed
+  // and quick determination of who's responsible if it can't.
+  std::set<WatchedHandle*> ready_handles_;
+
+  DISALLOW_COPY_AND_ASSIGN(WatcherDispatcher);
+};
+
+}  // namespace edk
+}  // namespace mojo
+
+#endif  // MOJO_EDK_SYSTEM_WATCHER_DISPATCHER_H_