Mojo: Armed Watchers

mojo/edk/system/request_context.cc

 // 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.
 
 #include "mojo/edk/system/request_context.h"
 
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/threading/thread_local.h"
 
@@ skipping 18 matching lines @@
 }
 
 RequestContext::~RequestContext() {
   if (IsCurrent()) {
     // NOTE: Callbacks invoked by this destructor are allowed to initiate new
     // EDK requests on this thread, so we need to reset the thread-local context
     // pointer before calling them. We persist the original notification source
     // since we're starting over at the bottom of the stack.
     tls_context_->Set(nullptr);
 
-    MojoWatchNotificationFlags flags = MOJO_WATCH_NOTIFICATION_FLAG_NONE;
+    MojoWatcherNotificationFlags flags = MOJO_WATCHER_NOTIFICATION_FLAG_NONE;
     if (source_ == Source::SYSTEM)
-      flags |= MOJO_WATCH_NOTIFICATION_FLAG_FROM_SYSTEM;
+      flags |= MOJO_WATCHER_NOTIFICATION_FLAG_FROM_SYSTEM;
 
-    // We run all cancellation finalizers first. This is necessary because it's
-    // possible that one of the cancelled watchers has other pending finalizers
+    // We send all cancellation notifications first. This is necessary because
+    // it's possible that cancelled watches have other pending notifications
     // attached to this RequestContext.
     //
-    // From the application's perspective the watch has already been cancelled,
-    // so we have to honor our contract which guarantees no more notifications.
-    for (const scoped_refptr<Watcher>& watcher :
-            watch_cancel_finalizers_.container())
-      watcher->Cancel();
+    // From the application's perspective the watch is cancelled as soon as this
+    // notification is received, and dispatching the cancellation notification
+    // updates some internal Watch state to ensure no further notifications
+    // fire. Because notifications on a single Watch are mutually exclusive,
+    // this is sufficient to guarantee that MOJO_RESULT_CANCELLED is the last
+    // notification received; which is the guarantee the API makes.
+    for (const scoped_refptr<Watch>& watch :
+         watch_cancel_finalizers_.container()) {
+      static const HandleSignalsState closed_state = {0, 0};
+
+      // Establish a new RequestContext to capture and run any new notifications
+      // triggered by the callback invocation.
+      RequestContext inner_context(source_);
+      watch->InvokeCallback(MOJO_RESULT_CANCELLED, closed_state, flags);
+    }
 
     for (const WatchNotifyFinalizer& watch :
-        watch_notify_finalizers_.container()) {
-      // Establish a new request context for the extent of each callback to
-      // ensure that they don't themselves invoke callbacks while holding a
-      // watcher lock.
-      RequestContext request_context(source_);
-      watch.watcher->MaybeInvokeCallback(watch.result, watch.state, flags);
+         watch_notify_finalizers_.container()) {
+      RequestContext inner_context(source_);
+      watch.watch->InvokeCallback(watch.result, watch.state, flags);
     }
   } else {
     // It should be impossible for nested contexts to have finalizers.
     DCHECK(watch_notify_finalizers_.container().empty());
     DCHECK(watch_cancel_finalizers_.container().empty());
   }
 }
 
 // static
 RequestContext* RequestContext::current() {
   DCHECK(g_current_context.Pointer()->Get());
   return g_current_context.Pointer()->Get();
 }
 
-void RequestContext::AddWatchNotifyFinalizer(
-    scoped_refptr<Watcher> watcher,
-    MojoResult result,
-    const HandleSignalsState& state) {
+void RequestContext::AddWatchNotifyFinalizer(scoped_refptr<Watch> watch,
+                                             MojoResult result,
+                                             const HandleSignalsState& state) {
   DCHECK(IsCurrent());
   watch_notify_finalizers_->push_back(
-      WatchNotifyFinalizer(std::move(watcher), result, state));
+      WatchNotifyFinalizer(std::move(watch), result, state));
 }
 
-void RequestContext::AddWatchCancelFinalizer(scoped_refptr<Watcher> watcher) {
+void RequestContext::AddWatchCancelFinalizer(scoped_refptr<Watch> watch) {
   DCHECK(IsCurrent());
-  watch_cancel_finalizers_->push_back(std::move(watcher));
+  watch_cancel_finalizers_->push_back(std::move(watch));
 }
 
 bool RequestContext::IsCurrent() const {
   return tls_context_->Get() == this;
 }
 
 RequestContext::WatchNotifyFinalizer::WatchNotifyFinalizer(
-    scoped_refptr<Watcher> watcher,
+    scoped_refptr<Watch> watch,
     MojoResult result,
     const HandleSignalsState& state)
-    : watcher(std::move(watcher)), result(result), state(state) {}
+    : watch(std::move(watch)), result(result), state(state) {}
 
 RequestContext::WatchNotifyFinalizer::WatchNotifyFinalizer(
     const WatchNotifyFinalizer& other) = default;
 
 RequestContext::WatchNotifyFinalizer::~WatchNotifyFinalizer() {}
 
 }  // namespace edk
 }  // namespace mojo