cefpython/src/include/base/cef_bind_helpers.h at cefpython51 · pythonthings/cefpython · GitHub

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// Redistribution and use in source and binary forms, with or without

// modification, are permitted provided that the following conditions are

// met:

// * Redistributions of source code must retain the above copyright

// notice, this list of conditions and the following disclaimer.

// * Redistributions in binary form must reproduce the above

// copyright notice, this list of conditions and the following disclaimer

// in the documentation and/or other materials provided with the

// distribution.

// * Neither the name of Google Inc. nor the name Chromium Embedded

// Framework nor the names of its contributors may be used to endorse

// or promote products derived from this software without specific prior

// written permission.

// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR

// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT

// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// This defines a set of argument wrappers and related factory methods that

// can be used specify the refcounting and reference semantics of arguments

// that are bound by the Bind() function in base/bind.h.

// It also defines a set of simple functions and utilities that people want

// when using Callback<> and Bind().

// ARGUMENT BINDING WRAPPERS

// The wrapper functions are base::Unretained(), base::Owned(), base::Passed(),

// base::ConstRef(), and base::IgnoreResult().

// Unretained() allows Bind() to bind a non-refcounted class, and to disable

// refcounting on arguments that are refcounted objects.

// Owned() transfers ownership of an object to the Callback resulting from

// bind; the object will be deleted when the Callback is deleted.

// Passed() is for transferring movable-but-not-copyable types (eg. scoped_ptr)

// through a Callback. Logically, this signifies a destructive transfer of

// the state of the argument into the target function. Invoking

// Callback::Run() twice on a Callback that was created with a Passed()

// argument will CHECK() because the first invocation would have already

// transferred ownership to the target function.

// ConstRef() allows binding a constant reference to an argument rather

// than a copy.

// IgnoreResult() is used to adapt a function or Callback with a return type to

// one with a void return. This is most useful if you have a function with,

// say, a pesky ignorable bool return that you want to use with PostTask or

// something else that expect a Callback with a void return.

// EXAMPLE OF Unretained():

// class Foo {

// public:

// void func() { cout << "Foo:f" << endl; }

// };

// // In some function somewhere.

// Foo foo;

// Closure foo_callback =

// Bind(&Foo::func, Unretained(&foo));

// foo_callback.Run(); // Prints "Foo:f".

// Without the Unretained() wrapper on |&foo|, the above call would fail

// to compile because Foo does not support the AddRef() and Release() methods.

// EXAMPLE OF Owned():

// void foo(int* arg) { cout << *arg << endl }

// int* pn = new int(1);

// Closure foo_callback = Bind(&foo, Owned(pn));

// foo_callback.Run(); // Prints "1"

// *n = 2;

// foo_callback.Run(); // Prints "2"

// foo_callback.Reset(); // |pn| is deleted. Also will happen when

// // |foo_callback| goes out of scope.

// Without Owned(), someone would have to know to delete |pn| when the last

// reference to the Callback is deleted.

// EXAMPLE OF ConstRef():

// void foo(int arg) { cout << arg << endl }

// int n = 1;

// Closure no_ref = Bind(&foo, n);

// Closure has_ref = Bind(&foo, ConstRef(n));

// no_ref.Run(); // Prints "1"

// has_ref.Run(); // Prints "1"

// n = 2;

// no_ref.Run(); // Prints "1"

// has_ref.Run(); // Prints "2"

// Note that because ConstRef() takes a reference on |n|, |n| must outlive all

// its bound callbacks.

// EXAMPLE OF IgnoreResult():

// int DoSomething(int arg) { cout << arg << endl; }

// // Assign to a Callback with a void return type.

// Callback<void(int)> cb = Bind(IgnoreResult(&DoSomething));

// cb->Run(1); // Prints "1".

// // Prints "1" on |ml|.

// ml->PostTask(FROM_HERE, Bind(IgnoreResult(&DoSomething), 1);

// EXAMPLE OF Passed():

// void TakesOwnership(scoped_ptr<Foo> arg) { }

// scoped_ptr<Foo> CreateFoo() { return scoped_ptr<Foo>(new Foo()); }

// scoped_ptr<Foo> f(new Foo());

// // |cb| is given ownership of Foo(). |f| is now NULL.

// // You can use f.Pass() in place of &f, but it's more verbose.

// Closure cb = Bind(&TakesOwnership, Passed(&f));

// // Run was never called so |cb| still owns Foo() and deletes

// // it on Reset().

// cb.Reset();

// // |cb| is given a new Foo created by CreateFoo().

// cb = Bind(&TakesOwnership, Passed(CreateFoo()));

// // |arg| in TakesOwnership() is given ownership of Foo(). |cb|

// // no longer owns Foo() and, if reset, would not delete Foo().

// cb.Run(); // Foo() is now transferred to |arg| and deleted.

// cb.Run(); // This CHECK()s since Foo() already been used once.

// Passed() is particularly useful with PostTask() when you are transferring

// ownership of an argument into a task, but don't necessarily know if the

// task will always be executed. This can happen if the task is cancellable

// or if it is posted to a MessageLoopProxy.

// SIMPLE FUNCTIONS AND UTILITIES.

// DoNothing() - Useful for creating a Closure that does nothing when called.

// DeletePointer<T>() - Useful for creating a Closure that will delete a

// pointer when invoked. Only use this when necessary.

// In most cases MessageLoop::DeleteSoon() is a better

// fit.

#ifndef CEF_INCLUDE_BASE_CEF_BIND_HELPERS_H_

#define CEF_INCLUDE_BASE_CEF_BIND_HELPERS_H_

#pragma once

#if defined(BASE_BIND_HELPERS_H_)

// Do nothing if the Chromium header has already been included.

// This can happen in cases where Chromium code is used directly by the

// client application. When using Chromium code directly always include

// the Chromium header first to avoid type conflicts.

#elif defined(USING_CHROMIUM_INCLUDES)

// When building CEF include the Chromium header directly.

#include "base/bind_helpers.h"

#else // !USING_CHROMIUM_INCLUDES

// The following is substantially similar to the Chromium implementation.

// If the Chromium implementation diverges the below implementation should be

// updated to match.

#include "include/base/cef_basictypes.h"

#include "include/base/cef_callback.h"

#include "include/base/cef_template_util.h"

#include "include/base/cef_weak_ptr.h"

namespace base {

namespace cef_internal {

// Use the Substitution Failure Is Not An Error (SFINAE) trick to inspect T

// for the existence of AddRef() and Release() functions of the correct

// signature.

// http://en.wikipedia.org/wiki/Substitution_failure_is_not_an_error

// http://stackoverflow.com/questions/257288/is-it-possible-to-write-a-c-template-to-check-for-a-functions-existence

// http://stackoverflow.com/questions/4358584/sfinae-approach-comparison

// http://stackoverflow.com/questions/1966362/sfinae-to-check-for-inherited-member-functions

// The last link in particular show the method used below.

// For SFINAE to work with inherited methods, we need to pull some extra tricks

// with multiple inheritance. In the more standard formulation, the overloads

// of Check would be:

// template <typename C>

// Yes NotTheCheckWeWant(Helper<&C::TargetFunc>*);

// template <typename C>

// No NotTheCheckWeWant(...);

// static const bool value = sizeof(NotTheCheckWeWant<T>(0)) == sizeof(Yes);

// The problem here is that template resolution will not match

// C::TargetFunc if TargetFunc does not exist directly in C. That is, if

// TargetFunc in inherited from an ancestor, &C::TargetFunc will not match,

// |value| will be false. This formulation only checks for whether or

// not TargetFunc exist directly in the class being introspected.

// To get around this, we play a dirty trick with multiple inheritance.

// First, We create a class BaseMixin that declares each function that we

// want to probe for. Then we create a class Base that inherits from both T

// (the class we wish to probe) and BaseMixin. Note that the function

// signature in BaseMixin does not need to match the signature of the function

// we are probing for; thus it's easiest to just use void(void).

// Now, if TargetFunc exists somewhere in T, then &Base::TargetFunc has an

// ambiguous resolution between BaseMixin and T. This lets us write the

// following:

// template <typename C>

// No GoodCheck(Helper<&C::TargetFunc>*);

// template <typename C>

// Yes GoodCheck(...);

// static const bool value = sizeof(GoodCheck<Base>(0)) == sizeof(Yes);

// Notice here that the variadic version of GoodCheck() returns Yes here

// instead of No like the previous one. Also notice that we calculate |value|

// by specializing GoodCheck() on Base instead of T.

// We've reversed the roles of the variadic, and Helper overloads.

// GoodCheck(Helper<&C::TargetFunc>*), when C = Base, fails to be a valid

// substitution if T::TargetFunc exists. Thus GoodCheck<Base>(0) will resolve

// to the variadic version if T has TargetFunc. If T::TargetFunc does not

// exist, then &C::TargetFunc is not ambiguous, and the overload resolution

// will prefer GoodCheck(Helper<&C::TargetFunc>*).

// This method of SFINAE will correctly probe for inherited names, but it cannot

// typecheck those names. It's still a good enough sanity check though.

// Works on gcc-4.2, gcc-4.4, and Visual Studio 2008.

// TODO(ajwong): Move to ref_counted.h or template_util.h when we've vetted

// this works well.

// TODO(ajwong): Make this check for Release() as well.

// See http://crbug.com/82038.

template <typename T>

class SupportsAddRefAndRelease {

typedef char Yes[1];

typedef char No[2];

struct BaseMixin {

void AddRef();

};

// MSVC warns when you try to use Base if T has a private destructor, the

// common pattern for refcounted types. It does this even though no attempt to

// instantiate Base is made. We disable the warning for this definition.

#if defined(OS_WIN)

#pragma warning(push)

#pragma warning(disable:4624)

#endif

struct Base : public T, public BaseMixin {

};

#if defined(OS_WIN)

#pragma warning(pop)

#endif

template <void(BaseMixin::*)(void)> struct Helper {};

template <typename C>

static No& Check(Helper<&C::AddRef>*);

template <typename >

static Yes& Check(...);

public:

static const bool value = sizeof(Check<Base>(0)) == sizeof(Yes);

};

// Helpers to assert that arguments of a recounted type are bound with a

// scoped_refptr.

template <bool IsClasstype, typename T>

struct UnsafeBindtoRefCountedArgHelper : false_type {

};

template <typename T>

struct UnsafeBindtoRefCountedArgHelper<true, T>

: integral_constant<bool, SupportsAddRefAndRelease<T>::value> {

};

template <typename T>

struct UnsafeBindtoRefCountedArg : false_type {

};

template <typename T>

struct UnsafeBindtoRefCountedArg<T*>

: UnsafeBindtoRefCountedArgHelper<is_class<T>::value, T> {

};

template <typename T>

class HasIsMethodTag {

typedef char Yes[1];

typedef char No[2];

template <typename U>

static Yes& Check(typename U::IsMethod*);

template <typename U>

static No& Check(...);

public:

static const bool value = sizeof(Check<T>(0)) == sizeof(Yes);

};

template <typename T>

class UnretainedWrapper {

public:

explicit UnretainedWrapper(T* o) : ptr_(o) {}

T* get() const { return ptr_; }

private:

T* ptr_;

};

template <typename T>

class ConstRefWrapper {

public:

explicit ConstRefWrapper(const T& o) : ptr_(&o) {}

const T& get() const { return *ptr_; }

private:

const T* ptr_;

};

template <typename T>

struct IgnoreResultHelper {

explicit IgnoreResultHelper(T functor) : functor_(functor) {}

T functor_;

};

template <typename T>

struct IgnoreResultHelper<Callback<T> > {

explicit IgnoreResultHelper(const Callback<T>& functor) : functor_(functor) {}

const Callback<T>& functor_;

};

// An alternate implementation is to avoid the destructive copy, and instead

// specialize ParamTraits<> for OwnedWrapper<> to change the StorageType to

// a class that is essentially a scoped_ptr<>.

// The current implementation has the benefit though of leaving ParamTraits<>

// fully in callback_internal.h as well as avoiding type conversions during

// storage.

template <typename T>

class OwnedWrapper {

public:

explicit OwnedWrapper(T* o) : ptr_(o) {}

~OwnedWrapper() { delete ptr_; }

T* get() const { return ptr_; }

OwnedWrapper(const OwnedWrapper& other) {

ptr_ = other.ptr_;

other.ptr_ = NULL;

}

private:

mutable T* ptr_;

};

// PassedWrapper is a copyable adapter for a scoper that ignores const.

// It is needed to get around the fact that Bind() takes a const reference to

// all its arguments. Because Bind() takes a const reference to avoid

// unnecessary copies, it is incompatible with movable-but-not-copyable

// types; doing a destructive "move" of the type into Bind() would violate

// the const correctness.

// This conundrum cannot be solved without either C++11 rvalue references or

// a O(2^n) blowup of Bind() templates to handle each combination of regular

// types and movable-but-not-copyable types. Thus we introduce a wrapper type

// that is copyable to transmit the correct type information down into

// BindState<>. Ignoring const in this type makes sense because it is only

// created when we are explicitly trying to do a destructive move.

// Two notes:

// 1) PassedWrapper supports any type that has a "Pass()" function.

// This is intentional. The whitelisting of which specific types we

// support is maintained by CallbackParamTraits<>.

// 2) is_valid_ is distinct from NULL because it is valid to bind a "NULL"

// scoper to a Callback and allow the Callback to execute once.

template <typename T>

class PassedWrapper {

public:

explicit PassedWrapper(T scoper) : is_valid_(true), scoper_(scoper.Pass()) {}

PassedWrapper(const PassedWrapper& other)

: is_valid_(other.is_valid_), scoper_(other.scoper_.Pass()) {

}

T Pass() const {

CHECK(is_valid_);

is_valid_ = false;

return scoper_.Pass();

}

private:

mutable bool is_valid_;

mutable T scoper_;

};

// Unwrap the stored parameters for the wrappers above.

template <typename T>

struct UnwrapTraits {

typedef const T& ForwardType;

static ForwardType Unwrap(const T& o) { return o; }

};

template <typename T>

struct UnwrapTraits<UnretainedWrapper<T> > {

typedef T* ForwardType;

static ForwardType Unwrap(UnretainedWrapper<T> unretained) {

return unretained.get();

}

};

template <typename T>

struct UnwrapTraits<ConstRefWrapper<T> > {

typedef const T& ForwardType;

static ForwardType Unwrap(ConstRefWrapper<T> const_ref) {

return const_ref.get();

}

};

template <typename T>

struct UnwrapTraits<scoped_refptr<T> > {

typedef T* ForwardType;

static ForwardType Unwrap(const scoped_refptr<T>& o) { return o.get(); }

};

template <typename T>

struct UnwrapTraits<WeakPtr<T> > {

typedef const WeakPtr<T>& ForwardType;

static ForwardType Unwrap(const WeakPtr<T>& o) { return o; }

};

template <typename T>

struct UnwrapTraits<OwnedWrapper<T> > {

typedef T* ForwardType;

static ForwardType Unwrap(const OwnedWrapper<T>& o) {

return o.get();

}

};

template <typename T>

struct UnwrapTraits<PassedWrapper<T> > {

typedef T ForwardType;

static T Unwrap(PassedWrapper<T>& o) {

return o.Pass();

}

};

// Utility for handling different refcounting semantics in the Bind()

// function.

template <bool is_method, typename T>

struct MaybeRefcount;

template <typename T>

struct MaybeRefcount<false, T> {

static void AddRef(const T&) {}

static void Release(const T&) {}

};

template <typename T, size_t n>

struct MaybeRefcount<false, T[n]> {

static void AddRef(const T*) {}

static void Release(const T*) {}

};

template <typename T>

struct MaybeRefcount<true, T> {

static void AddRef(const T&) {}

static void Release(const T&) {}

};

template <typename T>

struct MaybeRefcount<true, T*> {

static void AddRef(T* o) { o->AddRef(); }

static void Release(T* o) { o->Release(); }

};

// No need to additionally AddRef() and Release() since we are storing a

// scoped_refptr<> inside the storage object already.

template <typename T>

struct MaybeRefcount<true, scoped_refptr<T> > {

static void AddRef(const scoped_refptr<T>& o) {}

static void Release(const scoped_refptr<T>& o) {}

};

template <typename T>

struct MaybeRefcount<true, const T*> {

static void AddRef(const T* o) { o->AddRef(); }

static void Release(const T* o) { o->Release(); }

};

// IsWeakMethod is a helper that determine if we are binding a WeakPtr<> to a

// method. It is used internally by Bind() to select the correct

// InvokeHelper that will no-op itself in the event the WeakPtr<> for

// the target object is invalidated.

// P1 should be the type of the object that will be received of the method.

template <bool IsMethod, typename P1>

struct IsWeakMethod : public false_type {};

template <typename T>

struct IsWeakMethod<true, WeakPtr<T> > : public true_type {};

template <typename T>

struct IsWeakMethod<true, ConstRefWrapper<WeakPtr<T> > > : public true_type {};

} // namespace cef_internal

template <typename T>

static inline cef_internal::UnretainedWrapper<T> Unretained(T* o) {

return cef_internal::UnretainedWrapper<T>(o);

}

template <typename T>

static inline cef_internal::ConstRefWrapper<T> ConstRef(const T& o) {

return cef_internal::ConstRefWrapper<T>(o);

}

template <typename T>

static inline cef_internal::OwnedWrapper<T> Owned(T* o) {

return cef_internal::OwnedWrapper<T>(o);

}

// We offer 2 syntaxes for calling Passed(). The first takes a temporary and

// is best suited for use with the return value of a function. The second

// takes a pointer to the scoper and is just syntactic sugar to avoid having

// to write Passed(scoper.Pass()).

template <typename T>

static inline cef_internal::PassedWrapper<T> Passed(T scoper) {

return cef_internal::PassedWrapper<T>(scoper.Pass());

}

template <typename T>

static inline cef_internal::PassedWrapper<T> Passed(T* scoper) {

return cef_internal::PassedWrapper<T>(scoper->Pass());

}

template <typename T>

static inline cef_internal::IgnoreResultHelper<T> IgnoreResult(T data) {

return cef_internal::IgnoreResultHelper<T>(data);

}

template <typename T>

static inline cef_internal::IgnoreResultHelper<Callback<T> >

IgnoreResult(const Callback<T>& data) {

return cef_internal::IgnoreResultHelper<Callback<T> >(data);

}

void DoNothing();

template<typename T>

void DeletePointer(T* obj) {

delete obj;

}

} // namespace base

#endif // !USING_CHROMIUM_INCLUDES

#endif // CEF_INCLUDE_BASE_CEF_BIND_HELPERS_H_

cefpython/src/include/base/cef_bind_helpers.h at cefpython51 · pythonthings/cefpython · GitHub

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