Repo created

TMessagesProj/jni/voip/webrtc/base/callback_helpers.h

@@ -0,0 +1,127 @@
+// Copyright (c) 2012 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.
+
+// This defines helpful methods for dealing with Callbacks.  Because Callbacks
+// are implemented using templates, with a class per callback signature, adding
+// methods to Callback<> itself is unattractive (lots of extra code gets
+// generated).  Instead, consider adding methods here.
+
+#ifndef BASE_CALLBACK_HELPERS_H_
+#define BASE_CALLBACK_HELPERS_H_
+
+#include <type_traits>
+#include <utility>
+
+#include "base/atomicops.h"
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/compiler_specific.h"
+#include "base/macros.h"
+#include "base/memory/ptr_util.h"
+
+namespace base {
+
+namespace internal {
+
+template <typename T>
+struct IsBaseCallbackImpl : std::false_type {};
+
+template <typename R, typename... Args>
+struct IsBaseCallbackImpl<OnceCallback<R(Args...)>> : std::true_type {};
+
+template <typename R, typename... Args>
+struct IsBaseCallbackImpl<RepeatingCallback<R(Args...)>> : std::true_type {};
+
+}  // namespace internal
+
+template <typename T>
+using IsBaseCallback = internal::IsBaseCallbackImpl<std::decay_t<T>>;
+
+// SFINAE friendly enabler allowing to overload methods for both Repeating and
+// OnceCallbacks.
+//
+// Usage:
+// template <template <typename> class CallbackType,
+//           ... other template args ...,
+//           typename = EnableIfIsBaseCallback<CallbackType>>
+// void DoStuff(CallbackType<...> cb, ...);
+template <template <typename> class CallbackType>
+using EnableIfIsBaseCallback =
+    std::enable_if_t<IsBaseCallback<CallbackType<void()>>::value>;
+
+namespace internal {
+
+template <typename... Args>
+class AdaptCallbackForRepeatingHelper final {
+ public:
+  explicit AdaptCallbackForRepeatingHelper(OnceCallback<void(Args...)> callback)
+      : callback_(std::move(callback)) {
+    DCHECK(callback_);
+  }
+
+  void Run(Args... args) {
+    if (subtle::NoBarrier_AtomicExchange(&has_run_, 1))
+      return;
+    DCHECK(callback_);
+    std::move(callback_).Run(std::forward<Args>(args)...);
+  }
+
+ private:
+  volatile subtle::Atomic32 has_run_ = 0;
+  base::OnceCallback<void(Args...)> callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(AdaptCallbackForRepeatingHelper);
+};
+
+}  // namespace internal
+
+// Wraps the given OnceCallback into a RepeatingCallback that relays its
+// invocation to the original OnceCallback on the first invocation. The
+// following invocations are just ignored.
+//
+// Note that this deliberately subverts the Once/Repeating paradigm of Callbacks
+// but helps ease the migration from old-style Callbacks. Avoid if possible; use
+// if necessary for migration. TODO(tzik): Remove it. https://crbug.com/730593
+template <typename... Args>
+RepeatingCallback<void(Args...)> AdaptCallbackForRepeating(
+    OnceCallback<void(Args...)> callback) {
+  using Helper = internal::AdaptCallbackForRepeatingHelper<Args...>;
+  return base::BindRepeating(&Helper::Run,
+                             std::make_unique<Helper>(std::move(callback)));
+}
+
+// ScopedClosureRunner is akin to std::unique_ptr<> for Closures. It ensures
+// that the Closure is executed no matter how the current scope exits.
+// If you are looking for "ScopedCallback", "CallbackRunner", or
+// "CallbackScoper" this is the class you want.
+class BASE_EXPORT ScopedClosureRunner {
+ public:
+  ScopedClosureRunner();
+  explicit ScopedClosureRunner(OnceClosure closure);
+  ~ScopedClosureRunner();
+
+  ScopedClosureRunner(ScopedClosureRunner&& other);
+
+  // Releases the current closure if it's set and replaces it with the closure
+  // from |other|.
+  ScopedClosureRunner& operator=(ScopedClosureRunner&& other);
+
+  // Calls the current closure and resets it, so it wont be called again.
+  void RunAndReset();
+
+  // Replaces closure with the new one releasing the old one without calling it.
+  void ReplaceClosure(OnceClosure closure);
+
+  // Releases the Closure without calling.
+  OnceClosure Release() WARN_UNUSED_RESULT;
+
+ private:
+  OnceClosure closure_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedClosureRunner);
+};
+
+}  // namespace base
+
+#endif  // BASE_CALLBACK_HELPERS_H_