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// 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_H_
#define MOJO_EDK_SYSTEM_WATCHER_H_
#include "base/callback.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/synchronization/lock.h"
#include "mojo/public/c/system/functions.h"
#include "mojo/public/c/system/types.h"
namespace mojo {
namespace edk {
struct HandleSignalsState;
// This object corresponds to a watch added by a single call to |MojoWatch()|.
//
// An event may occur at any time which should trigger a Watcher to run its
// callback, but the callback needs to be deferred until all EDK locks are
// released. At the same time, a watch may be cancelled at any time by
// |MojoCancelWatch()| and it is not OK for the callback to be invoked after
// that happens.
//
// Therefore a Watcher needs to have some associated thread-safe state to track
// its cancellation, which is why it's ref-counted.
class Watcher : public base::RefCountedThreadSafe<Watcher> {
public:
using WatchCallback = base::Callback<void(MojoResult,
const HandleSignalsState&,
MojoWatchNotificationFlags)>;
// Constructs a new Watcher which watches for |signals| to be satisfied on a
// handle and which invokes |callback| either when one such signal is
// satisfied, or all such signals become unsatisfiable.
Watcher(MojoHandleSignals signals, const WatchCallback& callback);
// Runs the Watcher's callback with the given arguments if it hasn't been
// cancelled yet.
void MaybeInvokeCallback(MojoResult result,
const HandleSignalsState& state,
MojoWatchNotificationFlags flags);
// Notifies the Watcher of a state change. This may result in the Watcher
// adding a finalizer to the current RequestContext to invoke its callback,
// cancellation notwithstanding.
void NotifyForStateChange(const HandleSignalsState& signals_state);
// Notifies the Watcher of handle closure. This always results in the Watcher
// adding a finalizer to the current RequestContext to invoke its callback,
// cancellation notwithstanding.
void NotifyClosed();
// Explicitly cancels the watch, guaranteeing that its callback will never be
// be invoked again.
void Cancel();
private:
friend class base::RefCountedThreadSafe<Watcher>;
~Watcher();
// The set of signals which are watched by this Watcher.
const MojoHandleSignals signals_;
// The callback to invoke with a result and signal state any time signals in
// |signals_| are satisfied or become permanently unsatisfiable.
const WatchCallback callback_;
// Guards |is_cancelled_|.
base::Lock lock_;
// Indicates whether the watch has been cancelled. A |Watcher| may exist for a
// brief period of time after being cancelled if it's been attached as a
// RequestContext finalizer. In such cases the callback must not be invoked,
// hence this flag.
bool is_cancelled_ = false;
DISALLOW_COPY_AND_ASSIGN(Watcher);
};
} // namespace edk
} // namespace mojo
#endif // MOJO_EDK_SYSTEM_WATCHER_H_
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