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Unified Diff: mojo/edk/system/watch.h

Issue 2725133002: Mojo: Armed Watchers (Closed)
Patch Set: . Created 3 years, 9 months ago
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Index: mojo/edk/system/watch.h
diff --git a/mojo/edk/system/watch.h b/mojo/edk/system/watch.h
new file mode 100644
index 0000000000000000000000000000000000000000..f277de991767d49d95c1239df1f335b3c90ff7c7
--- /dev/null
+++ b/mojo/edk/system/watch.h
@@ -0,0 +1,124 @@
+// 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_WATCH_H_
+#define MOJO_EDK_SYSTEM_WATCH_H_
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/synchronization/lock.h"
+#include "mojo/edk/system/atomic_flag.h"
+#include "mojo/edk/system/handle_signals_state.h"
+
+namespace mojo {
+namespace edk {
+
+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> {
+ public:
+ // 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);
+
+ // 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,
+ MojoWatcherNotificationFlags flags);
+
+ const scoped_refptr<Dispatcher>& dispatcher() const { return dispatcher_; }
+ uintptr_t context() const { return context_; }
+
+ MojoResult last_known_result() const {
+ AssertWatcherLockAcquired();
+ return last_known_result_;
+ }
+
+ MojoHandleSignalsState last_known_signals_state() const {
+ AssertWatcherLockAcquired();
+ return last_known_signals_state_;
+ }
+
+ bool ready() const {
+ AssertWatcherLockAcquired();
+ return last_known_result_ == MOJO_RESULT_OK ||
+ last_known_result_ == MOJO_RESULT_FAILED_PRECONDITION;
+ }
+
+ private:
+ friend class base::RefCountedThreadSafe<Watch>;
+
+ ~Watch();
+
+#if DCHECK_IS_ON()
+ void AssertWatcherLockAcquired() const;
+#else
+ void AssertWatcherLockAcquired() const {}
+#endif
+
+ const scoped_refptr<WatcherDispatcher> watcher_;
+ const scoped_refptr<Dispatcher> dispatcher_;
+ const uintptr_t context_;
+ const MojoHandleSignals signals_;
+
+ // 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;
+
+ DISALLOW_COPY_AND_ASSIGN(Watch);
+};
+
+} // namespace edk
+} // namespace mojo
+
+#endif // MOJO_EDK_SYSTEM_WATCH_H_

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