Add different behavior to AwakableList for "persistent" vs "one-shot" awakables.

mojo/edk/system/awakable_list.cc

 // Copyright 2013 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/awakable_list.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "mojo/edk/system/awakable.h"
 #include "mojo/edk/system/handle_signals_state.h"
 
 namespace mojo {
 namespace system {
 
 AwakableList::AwakableList() {}
 
 AwakableList::~AwakableList() {
   DCHECK(awakables_.empty());
 }
 
 void AwakableList::OnStateChange(const HandleSignalsState& old_state,
                                  const HandleSignalsState& new_state) {
   // Instead of deleting elements in-place, swap them with the last element and
   // erase the elements from the end.
   auto last = awakables_.end();
-  for (AwakeInfoList::iterator it = awakables_.begin(); it != last;) {
-    bool keep = true;
-    if (new_state.satisfies(it->signals) && !old_state.satisfies(it->signals)) {
-      keep = it->awakable->Awake(it->context, Awakable::AwakeReason::SATISFIED,
-                                 new_state);
-    } else if (!new_state.can_satisfy(it->signals) &&
-               old_state.can_satisfy(it->signals)) {
-      keep = it->awakable->Awake(
-          it->context, Awakable::AwakeReason::UNSATISFIABLE, new_state);
+  for (auto it = awakables_.begin(); it != last;) {
+    bool awoken = false;
+    if (it->persistent) {
+      // Persistent awakables are called for all changes on watched signals.
+      if ((new_state.satisfied_signals & it->signals) !=
+              (old_state.satisfied_signals & it->signals) ||
+          (new_state.satisfiable_signals & it->signals) !=
+              (old_state.satisfiable_signals & it->signals)) {
+        awoken = true;
+        it->awakable->Awake(it->context, Awakable::AwakeReason::CHANGED,
+                            new_state);
+      }
+    } else {
+      // One-shot awakables are only called on "leading edge" changes.
+      if (new_state.satisfies(it->signals) &&
+          !old_state.satisfies(it->signals)) {
+        awoken = true;
+        it->awakable->Awake(it->context, Awakable::AwakeReason::SATISFIED,
+                            new_state);
+      } else if (!new_state.can_satisfy(it->signals) &&
+                 old_state.can_satisfy(it->signals)) {
+        awoken = true;
+        it->awakable->Awake(it->context, Awakable::AwakeReason::UNSATISFIABLE,
+                            new_state);
+      }
     }
 
-    if (!keep) {
+    // Remove if the awakable was awoken and one-shot.
+    if (awoken && !it->persistent) {
       --last;
       std::swap(*it, *last);
     } else {
       ++it;
     }
   }
   awakables_.erase(last, awakables_.end());
 }
 
-void AwakableList::CancelAll() {
-  for (AwakeInfoList::iterator it = awakables_.begin(); it != awakables_.end();
-       ++it) {
+void AwakableList::CancelAndRemoveAll() {
+  for (auto it = awakables_.begin(); it != awakables_.end(); ++it) {
     it->awakable->Awake(it->context, Awakable::AwakeReason::CANCELLED,
                         HandleSignalsState());
   }
   awakables_.clear();
 }
 
 void AwakableList::Add(Awakable* awakable,
                        uint64_t context,
+                       bool persistent,
                        MojoHandleSignals signals) {
-  awakables_.push_back(AwakeInfo(awakable, signals, context));
+  awakables_.push_back(AwakeInfo(awakable, context, persistent, signals));
 }
 
 void AwakableList::Remove(bool match_context,
                           Awakable* awakable,
                           uint64_t context) {
   // We allow a thread to wait on the same handle multiple times simultaneously,
   // so we need to scan the entire list and remove all occurrences of |waiter|.
   auto last = awakables_.end();
   for (AwakeInfoList::iterator it = awakables_.begin(); it != last;) {
     if (it->awakable == awakable &&
         (!match_context || it->context == context)) {
       --last;
       std::swap(*it, *last);
     } else {
       ++it;
     }
   }
   awakables_.erase(last, awakables_.end());
 }
 
 }  // namespace system
 }  // namespace mojo