Revert of Mojo: Armed Watchers

mojo/public/cpp/system/simple_watcher.h

Index: mojo/public/cpp/system/simple_watcher.h
diff --git a/mojo/public/cpp/system/simple_watcher.h b/mojo/public/cpp/system/simple_watcher.h
deleted file mode 100644
index 5e5a7ea3a101a24eb8b1b293f32cf8554cc0cf0c..0000000000000000000000000000000000000000
--- a/mojo/public/cpp/system/simple_watcher.h
+++ /dev/null
@@ -1,211 +0,0 @@
-// 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_PUBLIC_CPP_SYSTEM_SIMPLE_WATCHER_H_
-#define MOJO_PUBLIC_CPP_SYSTEM_SIMPLE_WATCHER_H_
-
-#include "base/callback.h"
-#include "base/location.h"
-#include "base/macros.h"
-#include "base/memory/ref_counted.h"
-#include "base/memory/weak_ptr.h"
-#include "base/threading/thread_checker.h"
-#include "base/threading/thread_task_runner_handle.h"
-#include "mojo/public/c/system/types.h"
-#include "mojo/public/cpp/system/system_export.h"
-#include "mojo/public/cpp/system/watcher.h"
-
-namespace base {
-class SingleThreadTaskRunner;
-}
-
-namespace mojo {
-
-// This provides a convenient thread-bound watcher implementation to safely
-// watch a single handle, dispatching state change notifications to an arbitrary
-// SingleThreadTaskRunner running on the same thread as the SimpleWatcher.
-//
-// SimpleWatcher exposes the concept of "arming" from the low-level Watcher API.
-// In general, a SimpleWatcher must be "armed" in order to dispatch a single
-// notification, and must then be rearmed before it will dispatch another. For
-// more details, see the documentation for ArmingPolicy and the Arm() and
-// ArmOrNotify() methods below.
-class MOJO_CPP_SYSTEM_EXPORT SimpleWatcher {
- public:
-  // A callback to be called any time a watched handle changes state in some
-  // interesting way. The |result| argument indicates one of the following
-  // conditions depending on its value:
-  //
-  //   |MOJO_RESULT_OK|: One or more of the signals being watched is satisfied.
-  //
-  //   |MOJO_RESULT_FAILED_PRECONDITION|: None of the signals being watched can
-  //       ever be satisfied again.
-  //
-  //   |MOJO_RESULT_CANCELLED|: The watched handle has been closed. No further
-  //       notifications will be fired, as this equivalent to an implicit
-  //       CancelWatch().
-  //
-  // Note that unlike the first two conditions, this callback may be invoked
-  // with |MOJO_RESULT_CANCELLED| even while the SimpleWatcher is disarmed.
-  using ReadyCallback = base::Callback<void(MojoResult result)>;
-
-  // Selects how this SimpleWatcher is to be armed.
-  enum class ArmingPolicy {
-    // The SimpleWatcher is armed automatically on Watch() and rearmed again
-    // after every invocation of the ReadyCallback. There is no need to manually
-    // call Arm() on a SimpleWatcher using this policy. This mode is equivalent
-    // to calling ArmOrNotify() once after Watch() and once again after every
-    // dispatched notification in MANUAL mode.
-    //
-    // This provides a reasonable approximation of edge-triggered behavior,
-    // mitigating (but not completely eliminating) the potential for redundant
-    // notifications.
-    //
-    // NOTE: It is important when using AUTOMATIC policy that your ReadyCallback
-    // always attempt to change the state of the handle (e.g. read available
-    // messages on a message pipe.) Otherwise this will result in a potentially
-    // large number of avoidable redundant tasks.
-    //
-    // For perfect edge-triggered behavior, use MANUAL policy and manually Arm()
-    // the SimpleWatcher as soon as it becomes possible to do so again.
-    AUTOMATIC,
-
-    // The SimpleWatcher is never armed automatically. Arm() or ArmOrNotify()
-    // must be called manually before any non-cancellation notification can be
-    // dispatched to the ReadyCallback. See the documentation for Arm() and
-    // ArmNotify() methods below for more details.
-    MANUAL,
-  };
-
-  SimpleWatcher(const tracked_objects::Location& from_here,
-                ArmingPolicy arming_policy,
-                scoped_refptr<base::SingleThreadTaskRunner> runner =
-                    base::ThreadTaskRunnerHandle::Get());
-  ~SimpleWatcher();
-
-  // Indicates if the SimpleWatcher is currently watching a handle.
-  bool IsWatching() const;
-
-  // Starts watching |handle|. A SimpleWatcher may only watch one handle at a
-  // time, but it is safe to call this more than once as long as the previous
-  // watch has been cancelled (i.e. |IsWatching()| returns |false|.)
-  //
-  // If |handle| is not a valid watchable (message or data pipe) handle or
-  // |signals| is not a valid set of signals to watch, this returns
-  // |MOJO_RESULT_INVALID_ARGUMENT|.
-  //
-  // Otherwise |MOJO_RESULT_OK| is returned and the handle will be watched until
-  // either |handle| is closed, the SimpleWatcher is destroyed, or Cancel() is
-  // explicitly called.
-  //
-  // Once the watch is started, |callback| may be called at any time on the
-  // current thread until |Cancel()| is called or the handle is closed. Note
-  // that |callback| can be called for results other than
-  // |MOJO_RESULT_CANCELLED| only if the SimpleWatcher is currently armed. Use
-  // ArmingPolicy to configure how a SimpleWatcher is armed.
-  //
-  // |MOJO_RESULT_CANCELLED| may be dispatched even while the SimpleWatcher
-  // is disarmed, and no further notifications will be dispatched after that.
-  //
-  // Destroying the SimpleWatcher implicitly calls |Cancel()|.
-  MojoResult Watch(Handle handle,
-                   MojoHandleSignals signals,
-                   const ReadyCallback& callback);
-
-  // Cancels the current watch. Once this returns, the ReadyCallback previously
-  // passed to |Watch()| will never be called again for this SimpleWatcher.
-  //
-  // Note that when cancelled with an explicit call to |Cancel()| the
-  // ReadyCallback will not be invoked with a |MOJO_RESULT_CANCELLED| result.
-  void Cancel();
-
-  // Manually arms the SimpleWatcher.
-  //
-  // Arming the SimpleWatcher allows it to fire a single notification regarding
-  // some future relevant change in the watched handle's state. It's only valid
-  // to call Arm() while a handle is being watched (see Watch() above.)
-  //
-  // SimpleWatcher is always disarmed immediately before invoking its
-  // ReadyCallback and must be rearmed again before another notification can
-  // fire.
-  //
-  // If the watched handle already meets the watched signaling conditions -
-  // i.e., if it would have notified immediately once armed - the SimpleWatcher
-  // is NOT armed, and this call fails with a return value of
-  // |MOJO_RESULT_FAILED_PRECONDITION|. In that case, what would have been the
-  // result code for that immediate notification is instead placed in
-  // |*ready_result| if |ready_result| is non-null.
-  //
-  // If the watcher is successfully armed, this returns |MOJO_RESULT_OK| and
-  // |ready_result| is ignored.
-  MojoResult Arm(MojoResult* ready_result = nullptr);
-
-  // Manually arms the SimpleWatcher OR posts a task to invoke the ReadyCallback
-  // with the ready result of the failed arming attempt.
-  //
-  // This is meant as a convenient helper for a common usage of Arm(), and it
-  // ensures that the ReadyCallback will be invoked asynchronously again as soon
-  // as the watch's conditions are satisfied, assuming the SimpleWatcher isn't
-  // cancelled first.
-  //
-  // Unlike Arm() above, this can never fail.
-  void ArmOrNotify();
-
-  Handle handle() const { return handle_; }
-  ReadyCallback ready_callback() const { return callback_; }
-
-  // Sets the tag used by the heap profiler.
-  // |tag| must be a const string literal.
-  void set_heap_profiler_tag(const char* heap_profiler_tag) {
-    heap_profiler_tag_ = heap_profiler_tag;
-  }
-
- private:
-  class Context;
-
-  void OnHandleReady(scoped_refptr<const Context> context, MojoResult result);
-
-  base::ThreadChecker thread_checker_;
-
-  // The policy used to determine how this SimpleWatcher is armed.
-  const ArmingPolicy arming_policy_;
-
-  // The TaskRunner of this SimpleWatcher's owning thread. This field is safe to
-  // access from any thread.
-  const scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
-
-  // Whether |task_runner_| is the same as base::ThreadTaskRunnerHandle::Get()
-  // for the thread.
-  const bool is_default_task_runner_;
-
-  ScopedWatcherHandle watcher_handle_;
-
-  // A thread-safe context object corresponding to the currently active watch,
-  // if any.
-  scoped_refptr<Context> context_;
-
-  // Fields below must only be accessed on the SimpleWatcher's owning thread.
-
-  // The handle currently under watch. Not owned.
-  Handle handle_;
-
-  // The callback to call when the handle is signaled.
-  ReadyCallback callback_;
-
-  // Tracks if the SimpleWatcher has already notified of unsatisfiability. This
-  // is used to prevent redundant notifications in AUTOMATIC mode.
-  bool unsatisfiable_ = false;
-
-  // Tag used to ID memory allocations that originated from notifications in
-  // this watcher.
-  const char* heap_profiler_tag_ = nullptr;
-
-  base::WeakPtrFactory<SimpleWatcher> weak_factory_;
-
-  DISALLOW_COPY_AND_ASSIGN(SimpleWatcher);
-};
-
-}  // namespace mojo
-
-#endif  // MOJO_PUBLIC_CPP_SYSTEM_SIMPLE_WATCHER_H_