Introduce base::IgnoreReuse() to wrap OnceCallback into RepeatingCallback

base/callback_helpers.h

 // 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.
 //
 // ResetAndReturn(&cb) is like cb.Reset() but allows executing a callback (via a
 // move or copy) after the original callback is Reset().  This can be handy if
 // Run() reads/writes the variable holding the Callback.
 
 #ifndef BASE_CALLBACK_HELPERS_H_
 #define BASE_CALLBACK_HELPERS_H_
 
+#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 {
 
 template <typename Signature,
           internal::CopyMode copy_mode,
           internal::RepeatMode repeat_mode>
-base::Callback<Signature, copy_mode, repeat_mode> ResetAndReturn(
-    base::Callback<Signature, copy_mode, repeat_mode>* cb) {
-  base::Callback<Signature, copy_mode, repeat_mode> ret(std::move(*cb));
+Callback<Signature, copy_mode, repeat_mode> ResetAndReturn(
+    Callback<Signature, copy_mode, repeat_mode>* cb) {
+  Callback<Signature, copy_mode, repeat_mode> ret(std::move(*cb));
   DCHECK(!*cb);
   return ret;
 }
 
+namespace internal {
+
+template <typename... Args>
+class IgnoreReuseHelper final {
+ public:
+  explicit IgnoreReuseHelper(OnceCallback<void(Args...)> callback)
+      : callback_(std::move(callback)) {
+    DCHECK(callback_);
+  }
+
+  void Run(Args... args) {
+    if (!subtle::NoBarrier_AtomicExchange(&is_first_, 0))

[dcheng, 2017/04/18 06:45:39]

Nit: maybe naming would be slightly clearer by calling this has_run_ (and
flipping the meaning of 1 and 0)

[tzik, 2017/04/20 06:06:05]

Done.

+      return;
+    DCHECK(callback_);
+    std::move(callback_).Run(std::forward<Args>(args)...);
+  }
+
+ private:
+  volatile subtle::Atomic32 is_first_ = 1;
+  base::OnceCallback<void(Args...)> callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(IgnoreReuseHelper);
+};
+
+}  // 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.
+template <typename... Args>
+RepeatingCallback<void(Args...)> IgnoreReuse(
+    OnceCallback<void(Args...)> callback) {
+  using Helper = internal::IgnoreReuseHelper<Args...>;
+  return base::BindRepeating(&Helper::Run,
+                             base::MakeUnique<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.
 class BASE_EXPORT ScopedClosureRunner {
  public:
   ScopedClosureRunner();
   explicit ScopedClosureRunner(const Closure& closure);
   ~ScopedClosureRunner();
 
   ScopedClosureRunner(ScopedClosureRunner&& other);
 
@@ skipping 12 matching lines @@
 
  private:
   Closure closure_;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedClosureRunner);
 };
 
 }  // namespace base
 
 #endif  // BASE_CALLBACK_HELPERS_H_