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// Copyright (c) 2011 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 file contains utility functions and classes that help the
// implementation, and management of the Callback objects.
#ifndef BASE_CALLBACK_HELPERS_H_
#define BASE_CALLBACK_HELPERS_H_
#pragma once
#include "base/ref_counted.h"
namespace base {
namespace internal {
// InvokerStorageBase is used to provide an opaque handle that the Callback
// class can use to represent a function object with bound arguments. It
// behaves as an existential type that is used by a corresponding
// DoInvoke function to perform the function execution. This allows
// us to shield the Callback class from the types of the bound argument via
// "type erasure."
class InvokerStorageBase : public RefCountedThreadSafe<InvokerStorageBase> {
protected:
friend class RefCountedThreadSafe<InvokerStorageBase>;
virtual ~InvokerStorageBase() {}
};
// This structure exists purely to pass the returned |invoker_storage_| from
// Bind() to Callback while avoiding an extra AddRef/Release() pair.
//
// To do this, the constructor of Callback<> must take a const-ref. The
// reference must be to a const object otherwise the compiler will emit a
// warning about taking a reference to a temporary.
//
// Unfortunately, this means that the internal |invoker_storage_| field must
// be made mutable.
template <typename T>
struct InvokerStorageHolder {
explicit InvokerStorageHolder(T* invoker_storage)
: invoker_storage_(invoker_storage) {
}
mutable scoped_refptr<InvokerStorageBase> invoker_storage_;
};
template <typename T>
InvokerStorageHolder<T> MakeInvokerStorageHolder(T* o) {
return InvokerStorageHolder<T>(o);
}
} // namespace internal
} // namespace base
#endif // BASE_CALLBACK_HELPERS_H_
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