Create "Prebind" a wrapper to tr1::bind.

base/prebind.h

+// Copyright (c) 2009 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.
+
+#ifndef BASE_PREBIND_H
+#define BASE_PREBIND_H
+
+#include <tr1/functional>
+
+#include <base/ref_counted.h>
+#include <base/closure.h>  // For UnretainedWrapper
+#include <base/tracked.h>
+
+namespace base {
+
+class ThunkState : public RefCountedThreadSafe<ThunkState> {
+ public:
+  tracked_objects::Tracked tracked_;

[willchan no longer on Chromium, 2011/01/05 00:59:01]

Similar comment as I made on the ClosureState thing.  I think this is not
needed.  It should moved to Thunk and ThunkState should be removed.

[awong, 2011/01/05 03:17:42]

Okay, I whacked it for now.

+
+  // If we used a list here, we'd have really nice resource management.
+  ::std::tr1::function<void(void)> cleanup_;
+
+  template <typename T>
+  void RetainObject(T* obj) {
+    obj->AddRef();
+    cleanup_ = ::std::tr1::bind(&T::Release, obj);
+  }
+};
+
+template <typename O>
+struct RetainTraits;
+
+template <typename O>
+struct RetainTraits<O*> {
+  typedef O type;
+  static O* unwrap(O* o) { return o; }
+  static void RetainObject(ThunkState* state, O* o) {
+    state->RetainObject(o);
+  }
+};
+
+template <typename O>
+struct RetainTraits<UnretainedWrapper<O> > {
+  typedef O type;
+  static O* unwrap(const UnretainedWrapper<O>& o) { return o.get(); }
+  static void RetainObject(ThunkState* state, O* o) {}
+};
+
+template <typename Sig>
+class Thunk;

[willchan no longer on Chromium, 2011/01/05 00:59:01]

I'm not sure if thunk is as commonly used a term as callback.  If possible, I'd
like to see us use callback instead of thunk.

[awong, 2011/01/05 03:17:42]

I don't like Thunk either.  After we settle on a particular API type, we can fix
the names to something sane.

I just started using different names so people had something to refer to.

+
+template <typename R>
+class Thunk<R(void)> {
+ public:
+  typedef ::std::tr1::function<R(void)> ThunkType;
+  ThunkType f_;
+  scoped_refptr<ThunkState> state_;
+
+  explicit Thunk(ThunkType f) : f_(f), state_(new ThunkState()) {}
+
+  R operator()(void) {
+    return f_();
+  }
+};
+
+template <typename R, typename A0>
+class Thunk<R(A0)> {
+ public:
+  typedef ::std::tr1::function<R(A0)> ThunkType;
+  ThunkType f_;
+  scoped_refptr<ThunkState> state_;
+
+  explicit Thunk(ThunkType f) : f_(f), state_(new ThunkState()) {}
+
+  R operator()(A0& a0) {
+    return f_(a0);
+  }
+};
+
+template <typename R, typename A0, typename A1>
+class Thunk<R(A0, A1)> {
+ public:
+  typedef ::std::tr1::function<R(A0,A1)> ThunkType;
+  ThunkType f_;
+  ::std::tr1::function<void(void)> cleanup_;
+  scoped_refptr<ThunkState> state_;
+
+  explicit Thunk(ThunkType f) : f_(f), state_(new ThunkState()) {}
+
+  R operator()(const A0& a0, const A1& a1) {
+    return f_(a0, a1);
+  }
+};
+
+// Note that when declaring these template parameters, the types used in the
+// function signature MUST not be shared with the types used in the arguments.
+// If they are shared, then automatic conversions break. For example, this
+// should work:
+//
+//   void foo(double d);
+//   function<void(void)> f = Prebind(&foo, 2);
+//
+// However, if you declare the template for prebind as follows:
+//
+//   template <typename R, typename P0>
+//   function<R(void)> Prebind(R(*)(P0), P0 p0);
+//
+// Then the line invoking Prebind will fail because 2 is an integer, and P0 is
+// locked to be a double.  If instead, you declare the template to not tie the
+// function signature directly to the parameters, the compiler will have the
+// flexibility to do the right conversion.  Thus, the correct declaration will
+// look like this:
+//
+//   template <typename R, typename X0, typename P0>
+//   function<R(void)> Prebind(R(*)(X0), P0 p0);
+//
+// The signature uses the type X0, and the argument uses the type P0.  There is
+// no directly relationship enforced by the template declaration. Instead, we
+// rely on the compiler to output in an error of P0 is not converatble to X0.
+//
+
+
+// 1 -> 0
+template <typename R, typename X0, typename P0>
+Thunk<R(void)>
+Prebind(R(*f)(P0), P0 p0) {
+  return Thunk<R(void)>(::std::tr1::bind(f, p0));
+}
+
+// 2 -> 0
+template <typename R, typename X0, typename X1, typename P0, typename P1>
+Thunk<R(void)>
+Prebind(R(*f)(X0, X1), P0 p0, P1 p1) {
+  return Thunk<R(void)>(::std::tr1::bind(f, p0, p1));
+}
+
+// 2 -> 1
+template <typename R, typename X0, typename P0, typename A0>
+Thunk<R(A0)>
+Prebind(R(*f)(X0, A0), P0 p0) {
+  return Thunk<R(A0)>(::std::tr1::bind(f, p0, ::std::tr1::placeholders::_1));
+}
+
+// (curry) 1 -> 0
+template <typename R, typename X0, typename P0>
+Thunk<R(void)>
+Prebind(Thunk<R(X0)> f, P0 p0) {
+  return Thunk<R(void)>(::std::tr1::bind(f, p0));
+}
+
+// (curry) 2 -> 0
+template <typename R, typename X0, typename X1, typename P0, typename P1>
+Thunk<R(void)>
+Prebind(Thunk<R(X0, X1)> f, P0 p0, P1 p1) {
+  return Thunk<R(void)>(::std::tr1::bind(f, p0, p1));
+}
+
+// (curry) 2 -> 1
+template <typename R, typename X0, typename P0, typename A0>
+Thunk<R(A0)>
+Prebind(Thunk<R(X0, A0)> f, P0 p0) {
+  return Thunk<R(A0)>(::std::tr1::bind(f, p0, ::std::tr1::placeholders::_1));
+}
+
+// Method 0 -> 0
+template <typename R, typename O, typename T>
+Thunk<R(void)>
+Prebind(R(O::*f)(), T t) {
+  typename RetainTraits<T>::type* object_(RetainTraits<T>::unwrap(t));
+  Thunk<R(void)> thunk(::std::tr1::bind(f, object_));
+  RetainTraits<T>::RetainObject(thunk.state_.get(), object_);
+  return thunk;
+}
+
+// Method 1 -> 0
+template <typename R, typename O, typename T, typename X0, typename P0>
+Thunk<R(void)>
+Prebind(R(O::*f)(X0), T t, P0 p0) {
+  typename RetainTraits<T>::type* object_(RetainTraits<T>::unwrap(t));
+  Thunk<R(void)> thunk(::std::tr1::bind(f, object_, p0));
+  RetainTraits<T>::RetainObject(thunk.state_.get(), object_);
+  return thunk;
+}
+
+// Method 1 -> 1
+template <typename R, typename O, typename T, typename A0>
+Thunk<R(A0)>
+Prebind(R(O::*f)(A0), T t) {
+  typename RetainTraits<T>::type* object_(RetainTraits<T>::unwrap(t));
+  Thunk<R(A0)> thunk(::std::tr1::bind(f, object_));
+  RetainTraits<T>::RetainObject(thunk.state_.get(), object_);
+  return thunk;
+}
+
+// Method 2 -> 0
+template <typename R, typename O, typename T, typename X0, typename X1, typename P0, typename P1>
+Thunk<R(void)>
+Prebind(R(O::*f)(X0, X1), T t, P0 p0, P1 p1) {
+  typename RetainTraits<T>::type* object_(RetainTraits<T>::unwrap(t));
+  Thunk<R(void)> thunk(::std::tr1::bind(f, object_, p0, p1));
+  RetainTraits<T>::RetainObject(thunk.state_.get(), object_);
+  return thunk;
+}
+
+// Method 2 -> 1
+template <typename R, typename O, typename T, typename X0, typename P0, typename A0>
+Thunk<R(A0)>
+Prebind(R(O::*f)(X0, A0), T t, P0 p0) {
+  typename RetainTraits<T>::type* object_(RetainTraits<T>::unwrap(t));
+  Thunk<R(A0)> thunk(::std::tr1::bind(f, object_, p0, ::std::tr1::placeholders::_1));
+  RetainTraits<T>::RetainObject(thunk.state_.get(), object_);
+  return thunk;
+}
+
+// Method 2 -> 2
+template <typename R, typename O, typename T, typename A0, typename A1>
+Thunk<R(A0, A1)>
+Prebind(R(O::*f)(A0, A1), T t) {
+  typename RetainTraits<T>::type* object_(RetainTraits<T>::unwrap(t));
+  Thunk<R(A0,A1)> thunk(::std::tr1::bind(f, object_,
+                                         ::std::tr1::placeholders::_1,
+                                         ::std::tr1::placeholders::_2));
+  RetainTraits<T>::RetainObject(thunk.state_.get(), object_);
+  return thunk;
+}
+
+// Method 5 -> 2  ...yeah, I skipped a few...got bored of typing it.
+template <typename R, typename O, typename T,
+         typename X0, typename X1, typename X2,
+         typename P0, typename P1, typename P2,
+         typename A0, typename A1>
+Thunk<R(A0, A1)>
+Prebind(R(O::*f)(X0, X1, X2, A0, A1), T t, P0 p0, P1 p1, P2 p2) {
+  O* object_(RetainTraits<T>::unwrap(t));
+  Thunk<R(A0,A1)> thunk(::std::tr1::bind(f, object_, p0, p1, p2,
+                                         ::std::tr1::placeholders::_1,
+                                         ::std::tr1::placeholders::_2));
+  RetainTraits<T>::RetainObject(thunk.state_.get(), object_);
+  return thunk;
+}
+
+// Wraps a Thunk to automatically cancel a task when the ThunkCanceller is
+// deleted.  This allows a caller to "nop" all outstanding callbacks registered
+// with the ThunkCanceller.
+//
+// Note that if you're also looking at the Closure code, this is nearly
+// identical to ClosureCanceller.  In fact, it can be used interchangeably, but
+// I put a forked version here just for completeness.
+class ThunkCanceller {
+ public:
+  ThunkCanceller() : cancel_state_(new CancelState()) {}
+
+  ~ThunkCanceller() {
+    cancel_state_->is_canceled = true;
+  }
+
+  template <typename T>
+  Thunk<void(void)> Wrap(T c) {
+    using ::std::tr1::bind;
+    return base::Thunk<void(void)>(Prebind(&ThunkCanceller::Run<T>, cancel_state_, c));
+  }
+
+  bool empty() const {
+    // The ThunkCanceller has the only reference, no tasks are outstanding.
+    return cancel_state_->HasOneRef();
+  }
+
+  void RevokeAll() {
+    // Cancel all outstanding, then create a new cancel state so this object may
+    // be reused.
+    cancel_state_->is_canceled = true;
+    cancel_state_ = new CancelState();
+  }
+
+ private:
+  // The ScopedRunnableMethodFactory uses a WeakPtr.  This is because it is
+  // actually reimplementing the storage for the task object, so a pointer is
+  // necessary and thus WeakPtr can be overloaded to serve as a flag.
+  //
+  // In this design, it seems overkill to use WeakPtr instead of a simple flag
+  // class (which WeakPtr eventually devolves into anyways).
+  class CancelState : public RefCounted<CancelState> {
+   public:
+    CancelState() : is_canceled(false) {}
+
+    bool is_canceled;
+  };
+
+  template <typename T>
+  static void Run(scoped_refptr<CancelState> cancel_state, T c) {
+    if (!cancel_state->is_canceled) {
+      c();
+    }
+  }
+
+  scoped_refptr<CancelState> cancel_state_;
+};
+
+}  // namespace base
+
+#endif  // BASE_PREBIND_H