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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.
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/synchronization/lock.h"
#include "mojo/core/atomic_flag.h"
#include "mojo/core/handle_signals_state.h"
#include "mojo/public/c/system/trap.h"
namespace mojo {
namespace core {
class Dispatcher;
class WatcherDispatcher;
// Encapsulates the state associated with a single watch context within a
// watcher.
// Every Watch has its own cancellation state, and is captured by RequestContext
// notification finalizers to avoid redundant context resolution during
// finalizer execution.
class Watch : public base::RefCountedThreadSafe<Watch> {
// Constructs a Watch which represents a watch within |watcher| associated
// with |context|, watching |dispatcher| for |signals|.
Watch(const scoped_refptr<WatcherDispatcher>& watcher,
const scoped_refptr<Dispatcher>& dispatcher,
uintptr_t context,
MojoHandleSignals signals,
MojoTriggerCondition condition);
// Notifies the Watch of a potential state change.
// If |allowed_to_call_callback| is true, this may add a notification
// finalizer to the current RequestContext to invoke the watcher's callback
// with this watch's context. See return values below.
// This is called directly by WatcherDispatcher whenever the Watch's observed
// dispatcher notifies the WatcherDispatcher of a state change.
// Returns |true| if the Watch entered or remains in a ready state as a result
// of the state change. If |allowed_to_call_callback| was true in this case,
// the Watch will have also attached a notification finalizer to the current
// RequestContext.
// Returns |false| if the
bool NotifyState(const HandleSignalsState& state,
bool allowed_to_call_callback);
// Notifies the watch of cancellation ASAP. This will always be the last
// notification sent for the watch.
void Cancel();
// Finalizer method for RequestContexts. This method is invoked once for every
// notification finalizer added to a RequestContext by this object. This calls
// down into the WatcherDispatcher to do the actual notification call.
void InvokeCallback(MojoResult result,
const HandleSignalsState& state,
MojoTrapEventFlags flags);
const scoped_refptr<Dispatcher>& dispatcher() const { return dispatcher_; }
uintptr_t context() const { return context_; }
MojoResult last_known_result() const {
return last_known_result_;
MojoHandleSignalsState last_known_signals_state() const {
return last_known_signals_state_;
bool ready() const {
return last_known_result_ == MOJO_RESULT_OK ||
friend class base::RefCountedThreadSafe<Watch>;
void AssertWatcherLockAcquired() const;
void AssertWatcherLockAcquired() const {}
const scoped_refptr<WatcherDispatcher> watcher_;
const scoped_refptr<Dispatcher> dispatcher_;
const uintptr_t context_;
const MojoHandleSignals signals_;
const MojoTriggerCondition condition_;
// The result code with which this Watch would notify if currently armed,
// based on the last known signaling state of |dispatcher_|. Guarded by the
// owning WatcherDispatcher's lock.
MojoResult last_known_result_ = MOJO_RESULT_UNKNOWN;
// The last known signaling state of |dispatcher_|. Guarded by the owning
// WatcherDispatcher's lock.
MojoHandleSignalsState last_known_signals_state_ = {0, 0};
// Guards |is_cancelled_| below and mutually excludes individual watch
// notification executions for this same watch context.
// Note that this should only be acquired from a RequestContext finalizer to
// ensure that no other internal locks are already held.
base::Lock notification_lock_;
// Guarded by |notification_lock_|.
bool is_cancelled_ = false;
} // namespace core
} // namespace mojo
#endif // MOJO_CORE_WATCH_H_