Motown: Move framework/util/incident* so other services can use it

services/media/framework/util/incident.h

-// 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_SERVICES_MEDIA_FRAMEWORK_UTIL_INCIDENT_H_
-#define MOJO_SERVICES_MEDIA_FRAMEWORK_UTIL_INCIDENT_H_
-
-#include <functional>
-#include <vector>
-
-#include "base/synchronization/lock.h"
-
-namespace mojo {
-namespace media {
-
-// The Incident class provides a facility for executing code as the consequence
-// of some occurrence. This can be useful for building state machines and
-// otherwise dealing with asynchronous operations.
-//
-// Incident is not a thread-safe class and has no ability to make a thread wait
-// or to execute code on a particular thread.
-//
-// Incidents rely heavily on std::function, so they shouldn't be used in
-// enormous numbers.
-//
-// An Incident can be in one of two states: initial state or occurred state.
-//
-// Code can be executed when an incident occurs:
-//
-//     incident.When([]() {
-//       // Do something...
-//     });
-//
-// The behavior of the When method depends on the incident's state. In initial
-// state, the consequence is added to a list to be executed when the incident
-// occurs. In occurred state, When executes the consequence immediately (before
-// When returns).
-//
-// An Incident occurs when its Occur (or Run) method is invoked and the Incident
-// is in the initial state. All registered consequences of the Incident are
-// executed during the call to Occur in the order they were added. Subsequent
-// calls to Occur are ignored until the Incident is reset.
-//
-// The Reset method ensures that the Incident is in its initial state and that
-// the list of consequences is cleared (without running the consequences).
-class Incident {
- public:
-  Incident();
-
-  ~Incident();
-
-  // Determines if this Incident has occurred due to a past call to Occur.
-  bool occurred() { return occurred_; }
-
-  // Executes the consequence when this Incident occurs. If this Incident hasn't
-  // occurred when this method is called, a copy of the consequence is held
-  // until this Incident occurs or is reset. If this Incident has occurred when
-  // this method is called, the consequence is executed immediately and no copy
-  // of the consequence is held.
-  void When(const std::function<void()>& consequence) {
-    if (occurred_) {
-      consequence();
-    } else {
-      consequences_.push_back(consequence);
-    }
-  }
-
-  // If this Incident is in inital state (!occurred()), this method makes this
-  // Incident occur, executing and deleting all its consequences. Otherwise,
-  // does nothing.
-  void Occur();
-
-  // Resets this Incident to initial state and clears the list of consequences.
-  void Reset() {
-    occurred_ = false;
-    consequences_.clear();
-  }
-
-  // Calls Occur. This method makes an Incident convertible to
-  // mojo::Callback<void()>.
-  void Run() { Occur(); }
-
- private:
-  bool occurred_ = false;
-  std::vector<std::function<void()>> consequences_;
-};
-
-// Like Incident, but threadsafe.
-class ThreadsafeIncident {
- public:
-  ThreadsafeIncident();
-
-  ~ThreadsafeIncident();
-
-  // Determines if this ThreadsafeIncident has occurred due to a past call to
-  // Occur. Note that the state of the this ThreadsafeIncident may change
-  // immediately after this method returns, so there's no guarantee that the
-  // result is still valid.
-  bool occurred() {
-    base::AutoLock lock(consequences_lock_);
-    return occurred_;
-  }
-
-  // Executes the consequence when this ThreadsafeIncident occurs. If this
-  // ThreadsafeIncident hasn't occurred when this method is called, a copy of
-  // the consequence is held until this ThreadsafeIncident occurs or is reset.
-  // If this ThreadsafeIncident has occurred when this method is called, the
-  // consequence is executed immediately and no copy of the consequence is held.
-  // Note that this ThreadsafeIncident's internal lock is not held when the
-  // consequence is called. It's therefore possible for this ThreadsafeIncident
-  // to be reset between the time the decision is made to run the consequence
-  // and when the consequence is actually run.
-  void When(const std::function<void()>& consequence) {
-    {
-      base::AutoLock lock(consequences_lock_);
-      if (!occurred_) {
-        consequences_.push_back(consequence);
-        return;
-      }
-    }
-
-    consequence();
-  }
-
-  // If this ThreadsafeIncident is in inital state (!occurred()), this method
-  // makes this ThreadsafeIncident occur, executing and deleting all its
-  // consequences. Otherwise, does nothing.
-  void Occur();
-
-  // Resets this ThreadsafeIncident to initial state and clears the list of
-  // consequences.
-  void Reset() {
-    base::AutoLock lock(consequences_lock_);
-    occurred_ = false;
-    consequences_.clear();
-  }
-
-  // Calls Occur. This method makes an ThreadsafeIncident convertible to
-  // mojo::Callback<void()>.
-  void Run() { Occur(); }
-
- private:
-  mutable base::Lock consequences_lock_;
-  bool occurred_ = false;
-  std::vector<std::function<void()>> consequences_;
-};
-
-}  // namespace media
-}  // namespace mojo
-
-#endif  // MOJO_SERVICES_MEDIA_FRAMEWORK_UTIL_INCIDENT_H_