The Tor Browser: security/sandbox/chromium/base/callback

security/sandbox/chromium/base/callback_internal.h@925c144e1f1f (annotated)

security/sandbox/chromium/base/callback_internal.h

Fri, 16 Jan 2015 18:13:44 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Fri, 16 Jan 2015 18:13:44 +0100
branch: TOR_BUG_9701
changeset 14: 925c144e1f1f
permissions: -rw-r--r--

Integrate suggestion from review to improve consistency with existing code.

 // 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 file contains utility functions and classes that help the
 // implementation, and management of the Callback objects.
 #ifndef BASE_CALLBACK_INTERNAL_H_
 #define BASE_CALLBACK_INTERNAL_H_
 #include <stddef.h>
 #include "base/base_export.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 template <typename T>
 class ScopedVector;
 namespace base {
 namespace internal {
 // BindStateBase 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 BindStateBase : public RefCountedThreadSafe<BindStateBase> {
  protected:
   friend class RefCountedThreadSafe<BindStateBase>;
   virtual ~BindStateBase() {}
 };
 // Holds the Callback methods that don't require specialization to reduce
 // template bloat.
 class BASE_EXPORT CallbackBase {
  public:
   // Returns true if Callback is null (doesn't refer to anything).
   bool is_null() const;
   // Returns the Callback into an uninitialized state.
   void Reset();
  protected:
   // In C++, it is safe to cast function pointers to function pointers of
   // another type. It is not okay to use void*. We create a InvokeFuncStorage
   // that that can store our function pointer, and then cast it back to
   // the original type on usage.
   typedef void(*InvokeFuncStorage)(void);
   // Returns true if this callback equals |other|. |other| may be null.
   bool Equals(const CallbackBase& other) const;
   // Allow initializing of |bind_state_| via the constructor to avoid default
   // initialization of the scoped_refptr.  We do not also initialize
   // |polymorphic_invoke_| here because doing a normal assignment in the
   // derived Callback templates makes for much nicer compiler errors.
   explicit CallbackBase(BindStateBase* bind_state);
   // Force the destructor to be instantiated inside this translation unit so
   // that our subclasses will not get inlined versions.  Avoids more template
   // bloat.
   ~CallbackBase();
   scoped_refptr<BindStateBase> bind_state_;
   InvokeFuncStorage polymorphic_invoke_;
 };
 // This is a typetraits object that's used to take an argument type, and
 // extract a suitable type for storing and forwarding arguments.
 //
 // In particular, it strips off references, and converts arrays to
 // pointers for storage; and it avoids accidentally trying to create a
 // "reference of a reference" if the argument is a reference type.
 //
 // This array type becomes an issue for storage because we are passing bound
 // parameters by const reference. In this case, we end up passing an actual
 // array type in the initializer list which C++ does not allow.  This will
 // break passing of C-string literals.
 template <typename T>
 struct CallbackParamTraits {
   typedef const T& ForwardType;
   typedef T StorageType;
 };
 // The Storage should almost be impossible to trigger unless someone manually
 // specifies type of the bind parameters.  However, in case they do,
 // this will guard against us accidentally storing a reference parameter.
 //
 // The ForwardType should only be used for unbound arguments.
 template <typename T>
 struct CallbackParamTraits<T&> {
   typedef T& ForwardType;
   typedef T StorageType;
 };
 // Note that for array types, we implicitly add a const in the conversion. This
 // means that it is not possible to bind array arguments to functions that take
 // a non-const pointer. Trying to specialize the template based on a "const
 // T[n]" does not seem to match correctly, so we are stuck with this
 // restriction.
 template <typename T, size_t n>
 struct CallbackParamTraits<T[n]> {
   typedef const T* ForwardType;
   typedef const T* StorageType;
 };
 // See comment for CallbackParamTraits<T[n]>.
 template <typename T>
 struct CallbackParamTraits<T[]> {
   typedef const T* ForwardType;
   typedef const T* StorageType;
 };
 // Parameter traits for movable-but-not-copyable scopers.
 //
 // Callback<>/Bind() understands movable-but-not-copyable semantics where
 // the type cannot be copied but can still have its state destructively
 // transferred (aka. moved) to another instance of the same type by calling a
 // helper function.  When used with Bind(), this signifies transferal of the
 // object's state to the target function.
 //
 // For these types, the ForwardType must not be a const reference, or a
 // reference.  A const reference is inappropriate, and would break const
 // correctness, because we are implementing a destructive move.  A non-const
 // reference cannot be used with temporaries which means the result of a
 // function or a cast would not be usable with Callback<> or Bind().
 //
 // TODO(ajwong): We might be able to use SFINAE to search for the existence of
 // a Pass() function in the type and avoid the whitelist in CallbackParamTraits
 // and CallbackForward.
 template <typename T, typename D>
 struct CallbackParamTraits<scoped_ptr<T, D> > {
   typedef scoped_ptr<T, D> ForwardType;
   typedef scoped_ptr<T, D> StorageType;
 };
 template <typename T, typename R>
 struct CallbackParamTraits<scoped_ptr_malloc<T, R> > {
   typedef scoped_ptr_malloc<T, R> ForwardType;
   typedef scoped_ptr_malloc<T, R> StorageType;
 };
 template <typename T>
 struct CallbackParamTraits<ScopedVector<T> > {
   typedef ScopedVector<T> ForwardType;
   typedef ScopedVector<T> StorageType;
 };
 // CallbackForward() is a very limited simulation of C++11's std::forward()
 // used by the Callback/Bind system for a set of movable-but-not-copyable
 // types.  It is needed because forwarding a movable-but-not-copyable
 // argument to another function requires us to invoke the proper move
 // operator to create a rvalue version of the type.  The supported types are
 // whitelisted below as overloads of the CallbackForward() function. The
 // default template compiles out to be a no-op.
 //
 // In C++11, std::forward would replace all uses of this function.  However, it
 // is impossible to implement a general std::forward with C++11 due to a lack
 // of rvalue references.
 //
 // In addition to Callback/Bind, this is used by PostTaskAndReplyWithResult to
 // simulate std::forward() and forward the result of one Callback as a
 // parameter to another callback. This is to support Callbacks that return
 // the movable-but-not-copyable types whitelisted above.
 template <typename T>
 T& CallbackForward(T& t) { return t; }
 template <typename T, typename D>
 scoped_ptr<T, D> CallbackForward(scoped_ptr<T, D>& p) { return p.Pass(); }
 template <typename T, typename R>
 scoped_ptr_malloc<T, R> CallbackForward(scoped_ptr_malloc<T, R>& p) {
   return p.Pass();
 }
 template <typename T>
 ScopedVector<T> CallbackForward(ScopedVector<T>& p) { return p.Pass(); }
 }  // namespace internal
 }  // namespace base
 #endif  // BASE_CALLBACK_INTERNAL_H_

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security/sandbox/chromium/base/callback_internal.h@925c144e1f1f (annotated)

security/sandbox/chromium/base/callback_internal.h