Mojo: Armed Watchers

mojo/edk/system/watch.cc

+// 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 "mojo/edk/system/watch.h"
+
+#include "mojo/edk/system/request_context.h"
+#include "mojo/edk/system/watcher_dispatcher.h"
+
+namespace mojo {
+namespace edk {
+
+Watch::Watch(const scoped_refptr<WatcherDispatcher>& watcher,
+             const scoped_refptr<Dispatcher>& dispatcher,
+             uintptr_t context,
+             MojoHandleSignals signals)
+    : watcher_(watcher),
+      dispatcher_(dispatcher),
+      context_(context),
+      signals_(signals) {}
+
+bool Watch::NotifyState(const HandleSignalsState& state,
+                        bool allowed_to_call_callback) {
+  AssertWatcherLockAcquired();
+
+  // NOTE: This method must NEVER call into |dispatcher_| directly, because it
+  // may be called while |dispatcher_| holds a lock.
+
+  MojoResult rv = MOJO_RESULT_SHOULD_WAIT;
+  RequestContext* const request_context = RequestContext::current();
+  if (state.satisfies(signals_)) {
+    rv = MOJO_RESULT_OK;
+    if (allowed_to_call_callback && rv != last_known_result_) {
+      request_context->AddWatchNotifyFinalizer(this, MOJO_RESULT_OK, state);
+    }
+  } else if (!state.can_satisfy(signals_)) {
+    rv = MOJO_RESULT_FAILED_PRECONDITION;
+    if (allowed_to_call_callback && rv != last_known_result_) {
+      request_context->AddWatchNotifyFinalizer(
+          this, MOJO_RESULT_FAILED_PRECONDITION, state);
+    }
+  }
+
+  last_known_signals_state_ =
+      *static_cast<const MojoHandleSignalsState*>(&state);
+  last_known_result_ = rv;
+  return ready();
+}
+
+void Watch::Cancel() {
+  RequestContext::current()->AddWatchCancelFinalizer(this);
+}
+
+void Watch::InvokeCallback(MojoResult result,
+                           const HandleSignalsState& state,
+                           MojoWatcherNotificationFlags flags) {
+  // We hold the lock through invocation to ensure that only one notification
+  // callback runs for this context at any given time.
+  base::AutoLock lock(notification_lock_);
+  if (result == MOJO_RESULT_CANCELLED) {
+    // Make sure cancellation is the last notification we dispatch.
+    DCHECK(!is_cancelled_);
+    is_cancelled_ = true;
+  } else if (is_cancelled_) {
+    return;
+  }
+
+  // NOTE: This will acquire |watcher_|'s internal lock. It's safe because a
+  // thread can only enter InvokeCallback() from within a RequestContext
+  // destructor where no dispatcher locks are held.
+  watcher_->InvokeWatchCallback(context_, result, state, flags);
+}
+
+Watch::~Watch() {}
+
+#if DCHECK_IS_ON()
+void Watch::AssertWatcherLockAcquired() const {
+  watcher_->lock_.AssertAcquired();
+}
+#endif
+
+}  // namespace edk
+}  // namespace mojo