Torne (Richard Coles) | 5821806 | 2012-11-14 11:43:16 +0000 | [diff] [blame] | 1 | $$ This is a pump file for generating file templates. Pump is a python |
| 2 | $$ script that is part of the Google Test suite of utilities. Description |
| 3 | $$ can be found here: |
| 4 | $$ |
| 5 | $$ http://code.google.com/p/googletest/wiki/PumpManual |
| 6 | $$ |
| 7 | |
| 8 | $$ See comment for MAX_ARITY in base/bind.h.pump. |
| 9 | $var MAX_ARITY = 7 |
| 10 | |
| 11 | // Copyright (c) 2012 The Chromium Authors. All rights reserved. |
| 12 | // Use of this source code is governed by a BSD-style license that can be |
| 13 | // found in the LICENSE file. |
| 14 | |
| 15 | #ifndef BASE_CALLBACK_H_ |
| 16 | #define BASE_CALLBACK_H_ |
| 17 | |
| 18 | #include "base/callback_forward.h" |
| 19 | #include "base/callback_internal.h" |
| 20 | #include "base/template_util.h" |
| 21 | |
| 22 | // NOTE: Header files that do not require the full definition of Callback or |
| 23 | // Closure should #include "base/callback_forward.h" instead of this file. |
| 24 | |
| 25 | // ----------------------------------------------------------------------------- |
| 26 | // Introduction |
| 27 | // ----------------------------------------------------------------------------- |
| 28 | // |
| 29 | // The templated Callback class is a generalized function object. Together |
| 30 | // with the Bind() function in bind.h, they provide a type-safe method for |
Torne (Richard Coles) | 2a99a7e | 2013-03-28 15:31:22 +0000 | [diff] [blame] | 31 | // performing partial application of functions. |
Torne (Richard Coles) | 5821806 | 2012-11-14 11:43:16 +0000 | [diff] [blame] | 32 | // |
Torne (Richard Coles) | 2a99a7e | 2013-03-28 15:31:22 +0000 | [diff] [blame] | 33 | // Partial application (or "currying") is the process of binding a subset of |
| 34 | // a function's arguments to produce another function that takes fewer |
| 35 | // arguments. This can be used to pass around a unit of delayed execution, |
| 36 | // much like lexical closures are used in other languages. For example, it |
| 37 | // is used in Chromium code to schedule tasks on different MessageLoops. |
Torne (Richard Coles) | 5821806 | 2012-11-14 11:43:16 +0000 | [diff] [blame] | 38 | // |
Torne (Richard Coles) | 2a99a7e | 2013-03-28 15:31:22 +0000 | [diff] [blame] | 39 | // A callback with no unbound input parameters (base::Callback<void(void)>) |
| 40 | // is called a base::Closure. Note that this is NOT the same as what other |
| 41 | // languages refer to as a closure -- it does not retain a reference to its |
| 42 | // enclosing environment. |
Torne (Richard Coles) | 5821806 | 2012-11-14 11:43:16 +0000 | [diff] [blame] | 43 | // |
| 44 | // MEMORY MANAGEMENT AND PASSING |
| 45 | // |
| 46 | // The Callback objects themselves should be passed by const-reference, and |
| 47 | // stored by copy. They internally store their state via a refcounted class |
| 48 | // and thus do not need to be deleted. |
| 49 | // |
| 50 | // The reason to pass via a const-reference is to avoid unnecessary |
| 51 | // AddRef/Release pairs to the internal state. |
| 52 | // |
| 53 | // |
| 54 | // ----------------------------------------------------------------------------- |
| 55 | // Quick reference for basic stuff |
| 56 | // ----------------------------------------------------------------------------- |
| 57 | // |
| 58 | // BINDING A BARE FUNCTION |
| 59 | // |
| 60 | // int Return5() { return 5; } |
| 61 | // base::Callback<int(void)> func_cb = base::Bind(&Return5); |
| 62 | // LOG(INFO) << func_cb.Run(); // Prints 5. |
| 63 | // |
| 64 | // BINDING A CLASS METHOD |
| 65 | // |
| 66 | // The first argument to bind is the member function to call, the second is |
| 67 | // the object on which to call it. |
| 68 | // |
| 69 | // class Ref : public base::RefCountedThreadSafe<Ref> { |
| 70 | // public: |
| 71 | // int Foo() { return 3; } |
| 72 | // void PrintBye() { LOG(INFO) << "bye."; } |
| 73 | // }; |
| 74 | // scoped_refptr<Ref> ref = new Ref(); |
| 75 | // base::Callback<void(void)> ref_cb = base::Bind(&Ref::Foo, ref); |
| 76 | // LOG(INFO) << ref_cb.Run(); // Prints out 3. |
| 77 | // |
| 78 | // By default the object must support RefCounted or you will get a compiler |
| 79 | // error. If you're passing between threads, be sure it's |
| 80 | // RefCountedThreadSafe! See "Advanced binding of member functions" below if |
| 81 | // you don't want to use reference counting. |
| 82 | // |
| 83 | // RUNNING A CALLBACK |
| 84 | // |
| 85 | // Callbacks can be run with their "Run" method, which has the same |
| 86 | // signature as the template argument to the callback. |
| 87 | // |
| 88 | // void DoSomething(const base::Callback<void(int, std::string)>& callback) { |
| 89 | // callback.Run(5, "hello"); |
| 90 | // } |
| 91 | // |
| 92 | // Callbacks can be run more than once (they don't get deleted or marked when |
| 93 | // run). However, this precludes using base::Passed (see below). |
| 94 | // |
| 95 | // void DoSomething(const base::Callback<double(double)>& callback) { |
| 96 | // double myresult = callback.Run(3.14159); |
| 97 | // myresult += callback.Run(2.71828); |
| 98 | // } |
| 99 | // |
| 100 | // PASSING UNBOUND INPUT PARAMETERS |
| 101 | // |
| 102 | // Unbound parameters are specified at the time a callback is Run(). They are |
| 103 | // specified in the Callback template type: |
| 104 | // |
| 105 | // void MyFunc(int i, const std::string& str) {} |
| 106 | // base::Callback<void(int, const std::string&)> cb = base::Bind(&MyFunc); |
| 107 | // cb.Run(23, "hello, world"); |
| 108 | // |
| 109 | // PASSING BOUND INPUT PARAMETERS |
| 110 | // |
| 111 | // Bound parameters are specified when you create thee callback as arguments |
| 112 | // to Bind(). They will be passed to the function and the Run()ner of the |
| 113 | // callback doesn't see those values or even know that the function it's |
| 114 | // calling. |
| 115 | // |
| 116 | // void MyFunc(int i, const std::string& str) {} |
| 117 | // base::Callback<void(void)> cb = base::Bind(&MyFunc, 23, "hello world"); |
| 118 | // cb.Run(); |
| 119 | // |
| 120 | // A callback with no unbound input parameters (base::Callback<void(void)>) |
| 121 | // is called a base::Closure. So we could have also written: |
| 122 | // |
| 123 | // base::Closure cb = base::Bind(&MyFunc, 23, "hello world"); |
| 124 | // |
| 125 | // When calling member functions, bound parameters just go after the object |
| 126 | // pointer. |
| 127 | // |
| 128 | // base::Closure cb = base::Bind(&MyClass::MyFunc, this, 23, "hello world"); |
| 129 | // |
| 130 | // PARTIAL BINDING OF PARAMETERS |
| 131 | // |
| 132 | // You can specify some parameters when you create the callback, and specify |
| 133 | // the rest when you execute the callback. |
| 134 | // |
| 135 | // void MyFunc(int i, const std::string& str) {} |
| 136 | // base::Callback<void(const std::string&)> cb = base::Bind(&MyFunc, 23); |
| 137 | // cb.Run("hello world"); |
| 138 | // |
| 139 | // When calling a function bound parameters are first, followed by unbound |
| 140 | // parameters. |
| 141 | // |
| 142 | // |
| 143 | // ----------------------------------------------------------------------------- |
| 144 | // Quick reference for advanced binding |
| 145 | // ----------------------------------------------------------------------------- |
| 146 | // |
| 147 | // BINDING A CLASS METHOD WITH WEAK POINTERS |
| 148 | // |
| 149 | // base::Bind(&MyClass::Foo, GetWeakPtr()); |
| 150 | // |
| 151 | // The callback will not be issued if the object is destroyed at the time |
| 152 | // it's issued. DANGER: weak pointers are not threadsafe, so don't use this |
| 153 | // when passing between threads! |
| 154 | // |
| 155 | // BINDING A CLASS METHOD WITH MANUAL LIFETIME MANAGEMENT |
| 156 | // |
| 157 | // base::Bind(&MyClass::Foo, base::Unretained(this)); |
| 158 | // |
| 159 | // This disables all lifetime management on the object. You're responsible |
| 160 | // for making sure the object is alive at the time of the call. You break it, |
| 161 | // you own it! |
| 162 | // |
| 163 | // BINDING A CLASS METHOD AND HAVING THE CALLBACK OWN THE CLASS |
| 164 | // |
| 165 | // MyClass* myclass = new MyClass; |
| 166 | // base::Bind(&MyClass::Foo, base::Owned(myclass)); |
| 167 | // |
| 168 | // The object will be deleted when the callback is destroyed, even if it's |
| 169 | // not run (like if you post a task during shutdown). Potentially useful for |
| 170 | // "fire and forget" cases. |
| 171 | // |
| 172 | // IGNORING RETURN VALUES |
| 173 | // |
| 174 | // Sometimes you want to call a function that returns a value in a callback |
| 175 | // that doesn't expect a return value. |
| 176 | // |
| 177 | // int DoSomething(int arg) { cout << arg << endl; } |
| 178 | // base::Callback<void<int>) cb = |
| 179 | // base::Bind(base::IgnoreResult(&DoSomething)); |
| 180 | // |
| 181 | // |
| 182 | // ----------------------------------------------------------------------------- |
| 183 | // Quick reference for binding parameters to Bind() |
| 184 | // ----------------------------------------------------------------------------- |
| 185 | // |
| 186 | // Bound parameters are specified as arguments to Bind() and are passed to the |
| 187 | // function. A callback with no parameters or no unbound parameters is called a |
| 188 | // Closure (base::Callback<void(void)> and base::Closure are the same thing). |
| 189 | // |
| 190 | // PASSING PARAMETERS OWNED BY THE CALLBACK |
| 191 | // |
| 192 | // void Foo(int* arg) { cout << *arg << endl; } |
| 193 | // int* pn = new int(1); |
| 194 | // base::Closure foo_callback = base::Bind(&foo, base::Owned(pn)); |
| 195 | // |
| 196 | // The parameter will be deleted when the callback is destroyed, even if it's |
| 197 | // not run (like if you post a task during shutdown). |
| 198 | // |
| 199 | // PASSING PARAMETERS AS A scoped_ptr |
| 200 | // |
| 201 | // void TakesOwnership(scoped_ptr<Foo> arg) {} |
| 202 | // scoped_ptr<Foo> f(new Foo); |
| 203 | // // f becomes null during the following call. |
| 204 | // base::Closure cb = base::Bind(&TakesOwnership, base::Passed(&f)); |
| 205 | // |
| 206 | // Ownership of the parameter will be with the callback until the it is run, |
| 207 | // when ownership is passed to the callback function. This means the callback |
| 208 | // can only be run once. If the callback is never run, it will delete the |
| 209 | // object when it's destroyed. |
| 210 | // |
| 211 | // PASSING PARAMETERS AS A scoped_refptr |
| 212 | // |
| 213 | // void TakesOneRef(scoped_refptr<Foo> arg) {} |
| 214 | // scoped_refptr<Foo> f(new Foo) |
| 215 | // base::Closure cb = base::Bind(&TakesOneRef, f); |
| 216 | // |
| 217 | // This should "just work." The closure will take a reference as long as it |
| 218 | // is alive, and another reference will be taken for the called function. |
| 219 | // |
| 220 | // PASSING PARAMETERS BY REFERENCE |
| 221 | // |
| 222 | // void foo(int arg) { cout << arg << endl } |
| 223 | // int n = 1; |
| 224 | // base::Closure has_ref = base::Bind(&foo, base::ConstRef(n)); |
| 225 | // n = 2; |
| 226 | // has_ref.Run(); // Prints "2" |
| 227 | // |
| 228 | // Normally parameters are copied in the closure. DANGER: ConstRef stores a |
| 229 | // const reference instead, referencing the original parameter. This means |
| 230 | // that you must ensure the object outlives the callback! |
| 231 | // |
| 232 | // |
| 233 | // ----------------------------------------------------------------------------- |
| 234 | // Implementation notes |
| 235 | // ----------------------------------------------------------------------------- |
| 236 | // |
| 237 | // WHERE IS THIS DESIGN FROM: |
| 238 | // |
| 239 | // The design Callback and Bind is heavily influenced by C++'s |
| 240 | // tr1::function/tr1::bind, and by the "Google Callback" system used inside |
| 241 | // Google. |
| 242 | // |
| 243 | // |
| 244 | // HOW THE IMPLEMENTATION WORKS: |
| 245 | // |
| 246 | // There are three main components to the system: |
| 247 | // 1) The Callback classes. |
| 248 | // 2) The Bind() functions. |
| 249 | // 3) The arguments wrappers (e.g., Unretained() and ConstRef()). |
| 250 | // |
| 251 | // The Callback classes represent a generic function pointer. Internally, |
| 252 | // it stores a refcounted piece of state that represents the target function |
| 253 | // and all its bound parameters. Each Callback specialization has a templated |
| 254 | // constructor that takes an BindState<>*. In the context of the constructor, |
| 255 | // the static type of this BindState<> pointer uniquely identifies the |
| 256 | // function it is representing, all its bound parameters, and a Run() method |
| 257 | // that is capable of invoking the target. |
| 258 | // |
| 259 | // Callback's constructor takes the BindState<>* that has the full static type |
| 260 | // and erases the target function type as well as the types of the bound |
| 261 | // parameters. It does this by storing a pointer to the specific Run() |
| 262 | // function, and upcasting the state of BindState<>* to a |
| 263 | // BindStateBase*. This is safe as long as this BindStateBase pointer |
| 264 | // is only used with the stored Run() pointer. |
| 265 | // |
| 266 | // To BindState<> objects are created inside the Bind() functions. |
| 267 | // These functions, along with a set of internal templates, are responsible for |
| 268 | // |
| 269 | // - Unwrapping the function signature into return type, and parameters |
| 270 | // - Determining the number of parameters that are bound |
| 271 | // - Creating the BindState storing the bound parameters |
| 272 | // - Performing compile-time asserts to avoid error-prone behavior |
| 273 | // - Returning an Callback<> with an arity matching the number of unbound |
| 274 | // parameters and that knows the correct refcounting semantics for the |
| 275 | // target object if we are binding a method. |
| 276 | // |
| 277 | // The Bind functions do the above using type-inference, and template |
| 278 | // specializations. |
| 279 | // |
| 280 | // By default Bind() will store copies of all bound parameters, and attempt |
| 281 | // to refcount a target object if the function being bound is a class method. |
Torne (Richard Coles) | 2a99a7e | 2013-03-28 15:31:22 +0000 | [diff] [blame] | 282 | // These copies are created even if the function takes parameters as const |
| 283 | // references. (Binding to non-const references is forbidden, see bind.h.) |
Torne (Richard Coles) | 5821806 | 2012-11-14 11:43:16 +0000 | [diff] [blame] | 284 | // |
| 285 | // To change this behavior, we introduce a set of argument wrappers |
| 286 | // (e.g., Unretained(), and ConstRef()). These are simple container templates |
| 287 | // that are passed by value, and wrap a pointer to argument. See the |
| 288 | // file-level comment in base/bind_helpers.h for more info. |
| 289 | // |
| 290 | // These types are passed to the Unwrap() functions, and the MaybeRefcount() |
| 291 | // functions respectively to modify the behavior of Bind(). The Unwrap() |
| 292 | // and MaybeRefcount() functions change behavior by doing partial |
| 293 | // specialization based on whether or not a parameter is a wrapper type. |
| 294 | // |
| 295 | // ConstRef() is similar to tr1::cref. Unretained() is specific to Chromium. |
| 296 | // |
| 297 | // |
| 298 | // WHY NOT TR1 FUNCTION/BIND? |
| 299 | // |
| 300 | // Direct use of tr1::function and tr1::bind was considered, but ultimately |
| 301 | // rejected because of the number of copy constructors invocations involved |
| 302 | // in the binding of arguments during construction, and the forwarding of |
| 303 | // arguments during invocation. These copies will no longer be an issue in |
| 304 | // C++0x because C++0x will support rvalue reference allowing for the compiler |
| 305 | // to avoid these copies. However, waiting for C++0x is not an option. |
| 306 | // |
| 307 | // Measured with valgrind on gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5), the |
| 308 | // tr1::bind call itself will invoke a non-trivial copy constructor three times |
| 309 | // for each bound parameter. Also, each when passing a tr1::function, each |
| 310 | // bound argument will be copied again. |
| 311 | // |
| 312 | // In addition to the copies taken at binding and invocation, copying a |
| 313 | // tr1::function causes a copy to be made of all the bound parameters and |
| 314 | // state. |
| 315 | // |
| 316 | // Furthermore, in Chromium, it is desirable for the Callback to take a |
| 317 | // reference on a target object when representing a class method call. This |
| 318 | // is not supported by tr1. |
| 319 | // |
| 320 | // Lastly, tr1::function and tr1::bind has a more general and flexible API. |
| 321 | // This includes things like argument reordering by use of |
| 322 | // tr1::bind::placeholder, support for non-const reference parameters, and some |
| 323 | // limited amount of subtyping of the tr1::function object (e.g., |
| 324 | // tr1::function<int(int)> is convertible to tr1::function<void(int)>). |
| 325 | // |
| 326 | // These are not features that are required in Chromium. Some of them, such as |
| 327 | // allowing for reference parameters, and subtyping of functions, may actually |
| 328 | // become a source of errors. Removing support for these features actually |
| 329 | // allows for a simpler implementation, and a terser Currying API. |
| 330 | // |
| 331 | // |
| 332 | // WHY NOT GOOGLE CALLBACKS? |
| 333 | // |
| 334 | // The Google callback system also does not support refcounting. Furthermore, |
| 335 | // its implementation has a number of strange edge cases with respect to type |
| 336 | // conversion of its arguments. In particular, the argument's constness must |
| 337 | // at times match exactly the function signature, or the type-inference might |
| 338 | // break. Given the above, writing a custom solution was easier. |
| 339 | // |
| 340 | // |
| 341 | // MISSING FUNCTIONALITY |
| 342 | // - Invoking the return of Bind. Bind(&foo).Run() does not work; |
| 343 | // - Binding arrays to functions that take a non-const pointer. |
| 344 | // Example: |
| 345 | // void Foo(const char* ptr); |
| 346 | // void Bar(char* ptr); |
| 347 | // Bind(&Foo, "test"); |
| 348 | // Bind(&Bar, "test"); // This fails because ptr is not const. |
| 349 | |
| 350 | namespace base { |
| 351 | |
| 352 | // First, we forward declare the Callback class template. This informs the |
| 353 | // compiler that the template only has 1 type parameter which is the function |
| 354 | // signature that the Callback is representing. |
| 355 | // |
| 356 | // After this, create template specializations for 0-$(MAX_ARITY) parameters. Note that |
| 357 | // even though the template typelist grows, the specialization still |
| 358 | // only has one type: the function signature. |
| 359 | // |
| 360 | // If you are thinking of forward declaring Callback in your own header file, |
| 361 | // please include "base/callback_forward.h" instead. |
| 362 | template <typename Sig> |
| 363 | class Callback; |
| 364 | |
| 365 | namespace internal { |
| 366 | template <typename Runnable, typename RunType, typename BoundArgsType> |
| 367 | struct BindState; |
| 368 | } // namespace internal |
| 369 | |
| 370 | |
| 371 | $range ARITY 0..MAX_ARITY |
| 372 | $for ARITY [[ |
| 373 | $range ARG 1..ARITY |
| 374 | |
| 375 | $if ARITY == 0 [[ |
| 376 | template <typename R> |
| 377 | class Callback<R(void)> : public internal::CallbackBase { |
| 378 | ]] $else [[ |
| 379 | template <typename R, $for ARG , [[typename A$(ARG)]]> |
| 380 | class Callback<R($for ARG , [[A$(ARG)]])> : public internal::CallbackBase { |
| 381 | ]] |
| 382 | |
| 383 | public: |
| 384 | typedef R(RunType)($for ARG , [[A$(ARG)]]); |
| 385 | |
| 386 | Callback() : CallbackBase(NULL) { } |
| 387 | |
| 388 | // Note that this constructor CANNOT be explicit, and that Bind() CANNOT |
| 389 | // return the exact Callback<> type. See base/bind.h for details. |
| 390 | template <typename Runnable, typename BindRunType, typename BoundArgsType> |
| 391 | Callback(internal::BindState<Runnable, BindRunType, |
| 392 | BoundArgsType>* bind_state) |
| 393 | : CallbackBase(bind_state) { |
| 394 | |
| 395 | // Force the assignment to a local variable of PolymorphicInvoke |
| 396 | // so the compiler will typecheck that the passed in Run() method has |
| 397 | // the correct type. |
| 398 | PolymorphicInvoke invoke_func = |
| 399 | &internal::BindState<Runnable, BindRunType, BoundArgsType> |
| 400 | ::InvokerType::Run; |
| 401 | polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func); |
| 402 | } |
| 403 | |
| 404 | bool Equals(const Callback& other) const { |
| 405 | return CallbackBase::Equals(other); |
| 406 | } |
| 407 | |
| 408 | R Run($for ARG , |
| 409 | [[typename internal::CallbackParamTraits<A$(ARG)>::ForwardType a$(ARG)]]) const { |
| 410 | PolymorphicInvoke f = |
| 411 | reinterpret_cast<PolymorphicInvoke>(polymorphic_invoke_); |
| 412 | |
| 413 | return f(bind_state_.get()[[]] |
| 414 | $if ARITY != 0 [[, ]] |
| 415 | $for ARG , |
| 416 | [[internal::CallbackForward(a$(ARG))]]); |
| 417 | } |
| 418 | |
| 419 | private: |
| 420 | typedef R(*PolymorphicInvoke)( |
| 421 | internal::BindStateBase*[[]] |
| 422 | $if ARITY != 0 [[, ]] |
| 423 | $for ARG , [[typename internal::CallbackParamTraits<A$(ARG)>::ForwardType]]); |
| 424 | |
| 425 | }; |
| 426 | |
| 427 | |
| 428 | ]] $$ for ARITY |
| 429 | |
| 430 | // Syntactic sugar to make Callbacks<void(void)> easier to declare since it |
| 431 | // will be used in a lot of APIs with delayed execution. |
| 432 | typedef Callback<void(void)> Closure; |
| 433 | |
| 434 | } // namespace base |
| 435 | |
| 436 | #endif // BASE_CALLBACK_H |