1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/security/sandbox/chromium/base/callback_internal.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,184 @@
1.4 +// Copyright (c) 2012 The Chromium Authors. All rights reserved.
1.5 +// Use of this source code is governed by a BSD-style license that can be
1.6 +// found in the LICENSE file.
1.7 +
1.8 +// This file contains utility functions and classes that help the
1.9 +// implementation, and management of the Callback objects.
1.10 +
1.11 +#ifndef BASE_CALLBACK_INTERNAL_H_
1.12 +#define BASE_CALLBACK_INTERNAL_H_
1.13 +
1.14 +#include <stddef.h>
1.15 +
1.16 +#include "base/base_export.h"
1.17 +#include "base/memory/ref_counted.h"
1.18 +#include "base/memory/scoped_ptr.h"
1.19 +
1.20 +template <typename T>
1.21 +class ScopedVector;
1.22 +
1.23 +namespace base {
1.24 +namespace internal {
1.25 +
1.26 +// BindStateBase is used to provide an opaque handle that the Callback
1.27 +// class can use to represent a function object with bound arguments. It
1.28 +// behaves as an existential type that is used by a corresponding
1.29 +// DoInvoke function to perform the function execution. This allows
1.30 +// us to shield the Callback class from the types of the bound argument via
1.31 +// "type erasure."
1.32 +class BindStateBase : public RefCountedThreadSafe<BindStateBase> {
1.33 + protected:
1.34 + friend class RefCountedThreadSafe<BindStateBase>;
1.35 + virtual ~BindStateBase() {}
1.36 +};
1.37 +
1.38 +// Holds the Callback methods that don't require specialization to reduce
1.39 +// template bloat.
1.40 +class BASE_EXPORT CallbackBase {
1.41 + public:
1.42 + // Returns true if Callback is null (doesn't refer to anything).
1.43 + bool is_null() const;
1.44 +
1.45 + // Returns the Callback into an uninitialized state.
1.46 + void Reset();
1.47 +
1.48 + protected:
1.49 + // In C++, it is safe to cast function pointers to function pointers of
1.50 + // another type. It is not okay to use void*. We create a InvokeFuncStorage
1.51 + // that that can store our function pointer, and then cast it back to
1.52 + // the original type on usage.
1.53 + typedef void(*InvokeFuncStorage)(void);
1.54 +
1.55 + // Returns true if this callback equals |other|. |other| may be null.
1.56 + bool Equals(const CallbackBase& other) const;
1.57 +
1.58 + // Allow initializing of |bind_state_| via the constructor to avoid default
1.59 + // initialization of the scoped_refptr. We do not also initialize
1.60 + // |polymorphic_invoke_| here because doing a normal assignment in the
1.61 + // derived Callback templates makes for much nicer compiler errors.
1.62 + explicit CallbackBase(BindStateBase* bind_state);
1.63 +
1.64 + // Force the destructor to be instantiated inside this translation unit so
1.65 + // that our subclasses will not get inlined versions. Avoids more template
1.66 + // bloat.
1.67 + ~CallbackBase();
1.68 +
1.69 + scoped_refptr<BindStateBase> bind_state_;
1.70 + InvokeFuncStorage polymorphic_invoke_;
1.71 +};
1.72 +
1.73 +// This is a typetraits object that's used to take an argument type, and
1.74 +// extract a suitable type for storing and forwarding arguments.
1.75 +//
1.76 +// In particular, it strips off references, and converts arrays to
1.77 +// pointers for storage; and it avoids accidentally trying to create a
1.78 +// "reference of a reference" if the argument is a reference type.
1.79 +//
1.80 +// This array type becomes an issue for storage because we are passing bound
1.81 +// parameters by const reference. In this case, we end up passing an actual
1.82 +// array type in the initializer list which C++ does not allow. This will
1.83 +// break passing of C-string literals.
1.84 +template <typename T>
1.85 +struct CallbackParamTraits {
1.86 + typedef const T& ForwardType;
1.87 + typedef T StorageType;
1.88 +};
1.89 +
1.90 +// The Storage should almost be impossible to trigger unless someone manually
1.91 +// specifies type of the bind parameters. However, in case they do,
1.92 +// this will guard against us accidentally storing a reference parameter.
1.93 +//
1.94 +// The ForwardType should only be used for unbound arguments.
1.95 +template <typename T>
1.96 +struct CallbackParamTraits<T&> {
1.97 + typedef T& ForwardType;
1.98 + typedef T StorageType;
1.99 +};
1.100 +
1.101 +// Note that for array types, we implicitly add a const in the conversion. This
1.102 +// means that it is not possible to bind array arguments to functions that take
1.103 +// a non-const pointer. Trying to specialize the template based on a "const
1.104 +// T[n]" does not seem to match correctly, so we are stuck with this
1.105 +// restriction.
1.106 +template <typename T, size_t n>
1.107 +struct CallbackParamTraits<T[n]> {
1.108 + typedef const T* ForwardType;
1.109 + typedef const T* StorageType;
1.110 +};
1.111 +
1.112 +// See comment for CallbackParamTraits<T[n]>.
1.113 +template <typename T>
1.114 +struct CallbackParamTraits<T[]> {
1.115 + typedef const T* ForwardType;
1.116 + typedef const T* StorageType;
1.117 +};
1.118 +
1.119 +// Parameter traits for movable-but-not-copyable scopers.
1.120 +//
1.121 +// Callback<>/Bind() understands movable-but-not-copyable semantics where
1.122 +// the type cannot be copied but can still have its state destructively
1.123 +// transferred (aka. moved) to another instance of the same type by calling a
1.124 +// helper function. When used with Bind(), this signifies transferal of the
1.125 +// object's state to the target function.
1.126 +//
1.127 +// For these types, the ForwardType must not be a const reference, or a
1.128 +// reference. A const reference is inappropriate, and would break const
1.129 +// correctness, because we are implementing a destructive move. A non-const
1.130 +// reference cannot be used with temporaries which means the result of a
1.131 +// function or a cast would not be usable with Callback<> or Bind().
1.132 +//
1.133 +// TODO(ajwong): We might be able to use SFINAE to search for the existence of
1.134 +// a Pass() function in the type and avoid the whitelist in CallbackParamTraits
1.135 +// and CallbackForward.
1.136 +template <typename T, typename D>
1.137 +struct CallbackParamTraits<scoped_ptr<T, D> > {
1.138 + typedef scoped_ptr<T, D> ForwardType;
1.139 + typedef scoped_ptr<T, D> StorageType;
1.140 +};
1.141 +
1.142 +template <typename T, typename R>
1.143 +struct CallbackParamTraits<scoped_ptr_malloc<T, R> > {
1.144 + typedef scoped_ptr_malloc<T, R> ForwardType;
1.145 + typedef scoped_ptr_malloc<T, R> StorageType;
1.146 +};
1.147 +
1.148 +template <typename T>
1.149 +struct CallbackParamTraits<ScopedVector<T> > {
1.150 + typedef ScopedVector<T> ForwardType;
1.151 + typedef ScopedVector<T> StorageType;
1.152 +};
1.153 +
1.154 +// CallbackForward() is a very limited simulation of C++11's std::forward()
1.155 +// used by the Callback/Bind system for a set of movable-but-not-copyable
1.156 +// types. It is needed because forwarding a movable-but-not-copyable
1.157 +// argument to another function requires us to invoke the proper move
1.158 +// operator to create a rvalue version of the type. The supported types are
1.159 +// whitelisted below as overloads of the CallbackForward() function. The
1.160 +// default template compiles out to be a no-op.
1.161 +//
1.162 +// In C++11, std::forward would replace all uses of this function. However, it
1.163 +// is impossible to implement a general std::forward with C++11 due to a lack
1.164 +// of rvalue references.
1.165 +//
1.166 +// In addition to Callback/Bind, this is used by PostTaskAndReplyWithResult to
1.167 +// simulate std::forward() and forward the result of one Callback as a
1.168 +// parameter to another callback. This is to support Callbacks that return
1.169 +// the movable-but-not-copyable types whitelisted above.
1.170 +template <typename T>
1.171 +T& CallbackForward(T& t) { return t; }
1.172 +
1.173 +template <typename T, typename D>
1.174 +scoped_ptr<T, D> CallbackForward(scoped_ptr<T, D>& p) { return p.Pass(); }
1.175 +
1.176 +template <typename T, typename R>
1.177 +scoped_ptr_malloc<T, R> CallbackForward(scoped_ptr_malloc<T, R>& p) {
1.178 + return p.Pass();
1.179 +}
1.180 +
1.181 +template <typename T>
1.182 +ScopedVector<T> CallbackForward(ScopedVector<T>& p) { return p.Pass(); }
1.183 +
1.184 +} // namespace internal
1.185 +} // namespace base
1.186 +
1.187 +#endif // BASE_CALLBACK_INTERNAL_H_
