206 lines
8.3 KiB
C
206 lines
8.3 KiB
C
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// Copyright (c) 2012 Google Inc. All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Google Inc. nor the name Chromium Embedded
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// Framework nor the names of its contributors may be used to endorse
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// or promote products derived from this software without specific prior
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// written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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// Do not include this header file directly. Use base/cef_bind.h or
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// base/cef_callback.h instead.
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// This file contains utility functions and classes that help the
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// implementation, and management of the Callback objects.
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#ifndef CEF_INCLUDE_BASE_INTERNAL_CEF_CALLBACK_INTERNAL_H_
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#define CEF_INCLUDE_BASE_INTERNAL_CEF_CALLBACK_INTERNAL_H_
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#include <stddef.h>
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#include "include/base/cef_ref_counted.h"
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#include "include/base/cef_scoped_ptr.h"
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template <typename T>
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class ScopedVector;
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namespace base {
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namespace cef_internal {
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// BindStateBase is used to provide an opaque handle that the Callback
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// class can use to represent a function object with bound arguments. It
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// behaves as an existential type that is used by a corresponding
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// DoInvoke function to perform the function execution. This allows
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// us to shield the Callback class from the types of the bound argument via
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// "type erasure."
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class BindStateBase : public RefCountedThreadSafe<BindStateBase> {
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protected:
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friend class RefCountedThreadSafe<BindStateBase>;
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virtual ~BindStateBase() {}
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};
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// Holds the Callback methods that don't require specialization to reduce
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// template bloat.
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class CallbackBase {
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public:
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// Returns true if Callback is null (doesn't refer to anything).
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bool is_null() const { return bind_state_.get() == NULL; }
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// Returns the Callback into an uninitialized state.
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void Reset();
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protected:
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// In C++, it is safe to cast function pointers to function pointers of
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// another type. It is not okay to use void*. We create a InvokeFuncStorage
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// that that can store our function pointer, and then cast it back to
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// the original type on usage.
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typedef void(*InvokeFuncStorage)(void);
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// Returns true if this callback equals |other|. |other| may be null.
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bool Equals(const CallbackBase& other) const;
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// Allow initializing of |bind_state_| via the constructor to avoid default
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// initialization of the scoped_refptr. We do not also initialize
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// |polymorphic_invoke_| here because doing a normal assignment in the
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// derived Callback templates makes for much nicer compiler errors.
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explicit CallbackBase(BindStateBase* bind_state);
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// Force the destructor to be instantiated inside this translation unit so
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// that our subclasses will not get inlined versions. Avoids more template
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// bloat.
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~CallbackBase();
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scoped_refptr<BindStateBase> bind_state_;
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InvokeFuncStorage polymorphic_invoke_;
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};
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// A helper template to determine if given type is non-const move-only-type,
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// i.e. if a value of the given type should be passed via .Pass() in a
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// destructive way.
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template <typename T> struct IsMoveOnlyType {
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template <typename U>
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static YesType Test(const typename U::MoveOnlyTypeForCPP03*);
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template <typename U>
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static NoType Test(...);
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static const bool value = sizeof(Test<T>(0)) == sizeof(YesType) &&
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!is_const<T>::value;
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};
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// This is a typetraits object that's used to take an argument type, and
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// extract a suitable type for storing and forwarding arguments.
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//
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// In particular, it strips off references, and converts arrays to
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// pointers for storage; and it avoids accidentally trying to create a
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// "reference of a reference" if the argument is a reference type.
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//
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// This array type becomes an issue for storage because we are passing bound
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// parameters by const reference. In this case, we end up passing an actual
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// array type in the initializer list which C++ does not allow. This will
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// break passing of C-string literals.
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template <typename T, bool is_move_only = IsMoveOnlyType<T>::value>
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struct CallbackParamTraits {
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typedef const T& ForwardType;
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typedef T StorageType;
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};
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// The Storage should almost be impossible to trigger unless someone manually
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// specifies type of the bind parameters. However, in case they do,
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// this will guard against us accidentally storing a reference parameter.
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//
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// The ForwardType should only be used for unbound arguments.
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template <typename T>
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struct CallbackParamTraits<T&, false> {
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typedef T& ForwardType;
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typedef T StorageType;
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};
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// Note that for array types, we implicitly add a const in the conversion. This
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// means that it is not possible to bind array arguments to functions that take
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// a non-const pointer. Trying to specialize the template based on a "const
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// T[n]" does not seem to match correctly, so we are stuck with this
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// restriction.
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template <typename T, size_t n>
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struct CallbackParamTraits<T[n], false> {
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typedef const T* ForwardType;
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typedef const T* StorageType;
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};
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// See comment for CallbackParamTraits<T[n]>.
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template <typename T>
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struct CallbackParamTraits<T[], false> {
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typedef const T* ForwardType;
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typedef const T* StorageType;
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};
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// Parameter traits for movable-but-not-copyable scopers.
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//
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// Callback<>/Bind() understands movable-but-not-copyable semantics where
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// the type cannot be copied but can still have its state destructively
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// transferred (aka. moved) to another instance of the same type by calling a
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// helper function. When used with Bind(), this signifies transferal of the
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// object's state to the target function.
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//
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// For these types, the ForwardType must not be a const reference, or a
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// reference. A const reference is inappropriate, and would break const
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// correctness, because we are implementing a destructive move. A non-const
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// reference cannot be used with temporaries which means the result of a
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// function or a cast would not be usable with Callback<> or Bind().
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template <typename T>
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struct CallbackParamTraits<T, true> {
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typedef T ForwardType;
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typedef T StorageType;
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};
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// CallbackForward() is a very limited simulation of C++11's std::forward()
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// used by the Callback/Bind system for a set of movable-but-not-copyable
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// types. It is needed because forwarding a movable-but-not-copyable
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// argument to another function requires us to invoke the proper move
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// operator to create a rvalue version of the type. The supported types are
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// whitelisted below as overloads of the CallbackForward() function. The
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// default template compiles out to be a no-op.
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//
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// In C++11, std::forward would replace all uses of this function. However, it
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// is impossible to implement a general std::forward with C++11 due to a lack
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// of rvalue references.
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//
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// In addition to Callback/Bind, this is used by PostTaskAndReplyWithResult to
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// simulate std::forward() and forward the result of one Callback as a
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// parameter to another callback. This is to support Callbacks that return
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// the movable-but-not-copyable types whitelisted above.
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template <typename T>
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typename enable_if<!IsMoveOnlyType<T>::value, T>::type& CallbackForward(T& t) {
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return t;
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}
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template <typename T>
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typename enable_if<IsMoveOnlyType<T>::value, T>::type CallbackForward(T& t) {
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return t.Pass();
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}
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} // namespace cef_internal
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} // namespace base
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#endif // CEF_INCLUDE_BASE_INTERNAL_CEF_CALLBACK_INTERNAL_H_
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