c++-gtk-utils
emitter.h
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1 /* Copyright (C) 2009 to 2014 Chris Vine
2 
3 The library comprised in this file or of which this file is part is
4 distributed by Chris Vine under the GNU Lesser General Public
5 License as follows:
6 
7  This library is free software; you can redistribute it and/or
8  modify it under the terms of the GNU Lesser General Public License
9  as published by the Free Software Foundation; either version 2.1 of
10  the License, or (at your option) any later version.
11 
12  This library is distributed in the hope that it will be useful, but
13  WITHOUT ANY WARRANTY; without even the implied warranty of
14  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15  Lesser General Public License, version 2.1, for more details.
16 
17  You should have received a copy of the GNU Lesser General Public
18  License, version 2.1, along with this library (see the file LGPL.TXT
19  which came with this source code package in the c++-gtk-utils
20  sub-directory); if not, write to the Free Software Foundation, Inc.,
21  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
22 
23 However, it is not intended that the object code of a program whose
24 source code instantiates a template from this file or uses macros or
25 inline functions (of any length) should by reason only of that
26 instantiation or use be subject to the restrictions of use in the GNU
27 Lesser General Public License. With that in mind, the words "and
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30 macros and small inline functions (ten lines or less in length)" in
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35 of the source code in this file).
36 
37 */
38 
39 #ifndef CGU_EMITTER_H
40 #define CGU_EMITTER_H
41 
42 /**
43  * @file emitter.h
44  * @brief This file provides a thread-safe signal/slot mechanism, with
45  * automatic disconnection.
46  *
47  * An EmitterArg object is a list of Callback::FunctorArg objects.
48  * Either callable objects (such as lambda expressions or the return
49  * value of std::bind) or Callback::FunctorArg objects may be
50  * "connected" to the EmitterArg object, and these will be executed
51  * when the operator()() or emit() member functions of the EmitterArg
52  * object concerned is called. They will be called in the order in
53  * which they were connected. Emitter is a typedef for
54  * EmitterArg<>. The generalised EmitterArg<T...> type contains
55  * Callback::FunctorArg<T...> objects or callable objects converted
56  * to Callback::FunctorArg<T...> objects (types T... being the
57  * unbound arguments the callback - see Cgu::Callback for further
58  * details, and "Usage" below for examples.) The Emitter type holds
59  * Callback::Functor (namely Callback::FunctorArg<>) objects.
60  *
61  * The main advantage of an emitter object as opposed to storing a
62  * functor object directly, apart from the fact that more than one
63  * functor can be dispatched by a single call to EmitterArg::emit() or
64  * EmitterArg::operator()(), is that it provides for automatic
65  * disconnection of a functor if the object whose member function it
66  * represents or calls into has ceased to exist.
67  *
68  * Where automatic disconnection is wanted, the object whose method is
69  * to be encapsulated by a functor must have a Releaser object as a
70  * public member. The Releaser object should be passed as the second
71  * argument of EmitterArg::connect(). As well as a Releaser object
72  * informing an emitter object when it has ceased to exist, an emitter
73  * object will do the same to the Releaser object if the emitter
74  * object happens to be destroyed before an object whose members it
75  * references or calls into (and therefore before the Releaser
76  * object). Automatic disconnection is mainly useful for non-static
77  * member functions, but it can be employed for static member
78  * functions or non-member functions if wanted (that will in effect
79  * bind the lifetime of the functor to that of the object to whose
80  * Releaser the functor has been attached.)
81  *
82  * It is safe for a connected function (i) to delete the EmitterArg
83  * object to which it is connected, even if there are other functors
84  * still to execute in the same emission (which will execute normally
85  * provided they do not try to call any of the emitter's functions),
86  * (ii) to call 'delete this' nothwithstanding that the connected
87  * functor is protected by a Releaser object (assuming all the other
88  * restraints on calling 'delete this' are met), provided that no
89  * other access would be made to the deleted object in a function call
90  * connected to the same emitter which is due to execute subsequently
91  * in the same emission, and (iii) to disconnect itself from the
92  * EmitterArg object. This design approach has a trade-off: if a
93  * connected functor tries to block, unblock or disconnect another
94  * functor connected to the same EmitterArg object which is due to
95  * execute subsequently in the same emission (or to block, unblock or
96  * disconnect itself when it is due to execute again subsequently in
97  * the same emission), the attempted block, unblock or disconnection
98  * will not have any effect on that emission (it will only have effect
99  * on a subsequent emission). In addition, a connected functor may
100  * not destroy an object which has a non-static method called by
101  * another functor connected to the same emitter and which would
102  * execute subsequently in the same emission, even if that object is
103  * protected by a Releaser object (the non-static method will
104  * unsuccessfully attempt to execute notwithstanding the destruction
105  * of the object it would be operating on).
106  *
107  * The SafeEmitterArg classes are the same as their EmitterArg
108  * counterparts except that they contain Callback::SafeFunctorArg
109  * objects, and their emit(), operator()(), connect(), disconnect(),
110  * block(), unblock() and destructor methods are protected by a mutex
111  * so that different threads can call these methods on the same
112  * emitter object, or create and delete the object.
113  *
114  * Note that the mutexes are released when the operator()()/emit()
115  * methods of the relevent Callback::SafeFunctorArg objects are
116  * called, as SafeEmitterArg objects have no idea what the referenced
117  * callbacks will do so if they were not released deadlocks could
118  * arise from recursive or out-of-order locking of the SafeEmitterArg
119  * mutex. It is therefore for users to provide additional
120  * synchronisation if the functions encapsulated by the relevant
121  * functors themselves need additional protection. Note also the
122  * subsidiary thread-safety points mentioned below.
123  *
124  * The Releaser class is intrinsically thread safe (the overhead of
125  * locking is so low that it is pointless having a separate
126  * unprotected class). This means that if a program is
127  * multi-threaded, you can use the plain EmitterArg classes provided
128  * that only the thread which creates a particular EmitterArg object
129  * calls connect(), block(), unblock((), emit() or operator()() on it,
130  * or deletes it, or calls disconnect() on it (either directly or
131  * through a Releaser object being destroyed). Where more than one
132  * thread might do that in relation to any one emitter object, use
133  * SafeEmitterArg.
134  *
135  * Alternatives
136  * ------------
137  *
138  * These classes are intended as a lightweight thread-safe signal/slot
139  * mechanism for GUI programming. For more demanding usage libsigc++
140  * is a good choice, except that it is not thread-safe. An
141  * alternative to libsigc++ is the boost::signal2 module, which is
142  * thread-safe.
143  *
144  * Subsidiary thread-safety points
145  * -------------------------------
146  *
147  * As mentioned, the SafeEmitterArg classes are thread safe, and their
148  * methods can be called in different threads without ill effect.
149  * However, there are some things that cannot be done. Users should
150  * observe two points.
151  *
152  * First, it has been mentioned that if a connected functor blocks,
153  * unblocks or disconnects another functor connected to the same
154  * emitter object and due to execute subsequently in the same
155  * emission, the blocking, unblocking or disconnection will not have
156  * effect in that emission, and that a connected functor may not
157  * delete an object whose non-static method is due to execute
158  * subsequently in the same emission. The same outcome would result
159  * if another thread tries to do any of these things while an emission
160  * is under way. Another thread should therefore leave alone objects
161  * connected to a SafeEmitterArg object from the time of operator()()
162  * or emit() beginning to the time of it ending, and not try to
163  * interfere.
164  *
165  * Secondly, when a Releaser object is passed as the second argument
166  * to the connect() method of a SafeEmitterArg object, the Releaser
167  * object must remain in existence until the connect() method returns
168  * or the emitter may be left in an inconsistent state.
169  *
170  * @anchor AssignmentAnchor
171  * Assignment
172  * ----------
173  *
174  * EmitterArg and SafeEmitterArg objects cannot be copied. Releaser
175  * objects can be (we do not want to make a class uncopiable just
176  * because it has the safety feature of having a Releaser object as a
177  * member).
178  *
179  * So how should assignment of a Releaser object and of a class which
180  * has a Releaser as a member be handled? An object which has a
181  * Releaser as a member and which is being assigned to (the assignee)
182  * could keep all its existing pre-assignment emitter connections - so
183  * far as the Releaser object is concerned, it will have to do so
184  * where the connections are not protected by the Releaser object, and
185  * we could do the same in relation to protected connections, in which
186  * case we would make operator=() of Releaser do nothing: that is,
187  * just return - a default assignment would always be wrong as it
188  * would take the assignor's Releaser state but inherit none of its
189  * connections, which the assignee cannot inherit as they depend on a
190  * remote emitter object or objects.
191  *
192  * However, the state of the assignee after assignment may not be such
193  * as to permit the inheriting of all the assignor's state except its
194  * connections. Accordingly, the default strategy adopted here is for
195  * the Releaser object to become a blank sheet on assignment. After
196  * assignment, an assignee which has a Releaser object as a member
197  * will no longer have any of the emitter connections which were,
198  * prior to assignment, protected by the Releaser object. If in a
199  * particular case the user does not want this behaviour, she should
200  * provide an assignment operator in the class which has Releaser as a
201  * member and leave Releaser alone in the assignment operator.
202  *
203  * Usage
204  * -----
205  *
206  * These are examples:
207  *
208  * @code
209  * using namespace Cgu;
210  *
211  * Emitter e1;
212  * e1.connect([] () {std::cout << "Hello world\n";});
213  * e1();
214  *
215  * SafeEmitter se1;
216  * se1.connect([] () {std::cout << "Hello world\n";});
217  * se1();
218  *
219  * int res;
220  * EmitterArg<int, int&> e2;
221  * e2.connect([] (int i, int& j) {j = 10 * i;});
222  * e2(2, res);
223  * std::cout << "10 times 2 is " << res << '\n';
224  *
225  * SafeEmitterArg<int, int&> se2;
226  * se2.connect([] (int i, int& j) {j = 10 * i;});
227  * se2(2, res);
228  * std::cout << "10 times 2 is " << res << '\n';
229  * @endcode
230  *
231  * Callback::FunctorArg and Callback::SafeFunctorArg objects may be
232  * connected to an emitter, and the connect() method may be directly
233  * initialized with the result of Callback::make(),
234  * Callback::make_ref() or Callback::lambda() and implicit conversion
235  * will take place. Here is an example using Callback::make_ref(),
236  * with a class object my_obj of type MyClass, with a method void
237  * MyClass::my_method(const Something&, int):
238  *
239  * @code
240  * using namespace Cgu;
241  *
242  * Something arg;
243  * SafeEmitterArg<int> se;
244  * se.connect(Callback::make_ref(my_obj, &MyClass::my_method, arg));
245  * se(5);
246  * @endcode
247  *
248  * EmitterArg classes do not provide for a return value. If a
249  * result is wanted, users should pass an unbound argument by
250  * reference or pointer (or pointer to pointer).
251  *
252  * Exception safety
253  * ----------------
254  *
255  * Apart from the emit()/operator()() and connect() methods, nothing
256  * done to an EmitterArg/SafeEmitterArg object should cause an
257  * exception to be thrown. This is because other methods only iterate
258  * through a std::list object using std::for_each(), std::find() or by
259  * hand, and the only things done by std::for_each() or after a
260  * std::find() or iteration is to remove a functor from the list
261  * (copying a functor and comparing functors never throw, nor does
262  * destroying a functor provided the destructors of any bound argument
263  * type do not throw). Thus, an EmitterArg/SafeEmitterArg and
264  * Releaser object should never get into an inconsistent state.
265  *
266  * The connect() method could throw a std::bad_alloc exception, either
267  * on creating new functors or on pushing the functors onto the list.
268  * However, were it to do so, the method has strong exception safety
269  * (assuming merely iterating over a list does not throw, as it should
270  * not).
271  *
272  * The emit()/operator()() methods could throw std::bad_alloc, and so
273  * far as that is concerned emission of all the connected functors
274  * will either all succeed or all fail. In addition, the functions
275  * represented by the functors held by the emitter might throw when
276  * executed. emit()/operator()() do not attempt to catch these
277  * exceptions as there is nothing they could do with them. This means
278  * that although a throwing connected functor will not leave the
279  * EmitterArg/SafeEmitterArg object in an inconsistent state, any
280  * other connected functors due to execute subsequently on that same
281  * emission will not execute. If that is important in any particular
282  * case, the user must incorporate logic in the connected functions to
283  * cater for an exception causing only part execution, or must connect
284  * only one functor to any one signal and "chain" emissions by hand so
285  * as to do the right thing.
286  */
287 
288 /*
289  Mutex locking heirarchy:
290 
291  Some out-of-order locking must take place because of the
292  relationship between the Releaser and SafeEmitterArg<> classes. The
293  mutex of Releaser is given the higher priority. This means that a
294  plain EmitterArg<> object will not take any hit from the fact that
295  Releaser is also useable with SafeEmitterArg<> objects.
296 
297  One consequence is that to avoid deadlocks, it is the
298  SafeEmitterArg<> functions which must yield when a deadlock would
299  otherwise arise. Yielding could occur in
300  SafeEmitterArg<>::~SafeEmitterArg() and
301  SafeEmitterArg<>::disconnect().
302 */
303 
304 #ifdef CGU_USE_SCHED_YIELD
305 #include <sched.h>
306 #else
307 #include <unistd.h>
308 #endif
309 
310 #include <list>
311 #include <unordered_set>
312 #include <algorithm>
313 #include <functional>
314 #include <utility> // for std::move
315 #include <type_traits> // for std::remove_reference, std::enable_if and std::is_convertible
316 
317 #include <c++-gtk-utils/callback.h>
318 #include <c++-gtk-utils/mutex.h>
320 
321 namespace Cgu {
322 
323 /* The four basic emitter types */
324 
325 template <class... FreeArgs> class EmitterArg;
326 template <class... FreeArgs> class SafeEmitterArg;
327 typedef EmitterArg<> Emitter;
329 
330 /**
331  * @class Releaser emitter.h c++-gtk-utils/emitter.h
332  * @brief A class used for tracking EmitterArg and SafeEmitterArg
333  * connections.
334  * @sa EmitterArg SafeEmitterArg
335  * @sa emitter.h
336  * @sa Callback namespace
337  *
338  * This class provides tracking of EmitterArg and SafeEmitterArg
339  * connections. It should be a public member of any target class
340  * which wants functors representing any of its methods to be
341  * disconnected automatically from an EmitterArg or SafeEmitterArg
342  * object when the target class object is destroyed, and is passed as
343  * one of the arguments to the connect() method of EmitterArg or
344  * SafeEmitterArg.
345  *
346  * All its methods are thread-safe.
347  *
348  * For further background, read this: emitter.h
349  */
350 
351 class Releaser {
352 
353  // from version 2.0.0-rc3 we use std::unordered_set rather than
354  // std::list in Releaser. We can't do that for
355  // EmitterArg/SafeEmitterArg objects, as they need to execute
356  // connected functors in the order in which they were connected.
357  std::unordered_set<Callback::SafeFunctor> disconnect_set;
358  Thread::Mutex mutex;
359 
360  // only an EmitterArg or SafeEmitterArg object can access add(), remove and try_remove()
361  void add(const Callback::SafeFunctor&);
362  void remove(const Callback::SafeFunctor&);
363  void try_remove(const Callback::SafeFunctor&, int*);
364 public:
365  template <class... T> friend class EmitterArg;
366  template <class... T> friend class SafeEmitterArg;
367 
368  // operator=() and the copy constructor should copy nothing from the
369  // assignor, because disconnect_set should be empty in the
370  // assignee, as any class containing us does not acquire as assignee
371  // any emitter functors representing any of its methods
372 
373 /**
374  * See notes on @ref AssignmentAnchor "assignment" to see how this
375  * operates. This does not throw provided that the destructors of any
376  * bound arguments of a functor managed by this Releaser object prior
377  * to assignment do not throw (as they should not do), and assuming
378  * that merely iterating through a list does not throw (as it would
379  * not on any sane implementation).
380  * @param r The assignee.
381  */
382  Releaser& operator=(const Releaser& r);
383 
384 /**
385  * This does not copy anything from the Releaser object passed as an
386  * argument - see the notes on @ref AssignmentAnchor "assignment" for
387  * an explanation of why. This does not throw.
388  * @param r A Releaser object.
389  * @exception std::bad_alloc This constructor might throw
390  * std::bad_alloc if memory is exhausted and the system throws in that
391  * case.
392  * @exception Thread::MutexError This constructor might throw
393  * Thread::MutexError if initialisation of the contained mutex fails.
394  * (It is often not worth checking for this, as it means either memory
395  * is exhausted or pthread has run out of other resources to create
396  * new mutexes.)
397  */
398  Releaser(const Releaser& r) {}
399 
400 /**
401  * @exception std::bad_alloc The default constructor might throw
402  * std::bad_alloc if memory is exhausted and the system throws in that
403  * case.
404  * @exception Thread::MutexError The default constructor might throw
405  * Thread::MutexError if initialisation of the contained mutex fails.
406  * (It is often not worth checking for this, as it means either memory
407  * is exhausted or pthread has run out of other resources to create
408  * new mutexes.)
409  */
410  Releaser() = default;
411 
412 /**
413  * The destructor does not throw provided that the destructors of any
414  * bound arguments of a functor managed by this Releaser object do not
415  * throw (as they should not do), and assuming that merely iterating
416  * through an unordered_set does not throw (as it would not on any
417  * sane implementation).
418  */
419  ~Releaser();
420 
421 /* Only has effect if --with-glib-memory-slices-compat or
422  * --with-glib-memory-slices-no-compat option picked */
424 };
425 
426 /* the emitter classes */
427 
428 /**
429  * @class EmitterArg emitter.h c++-gtk-utils/emitter.h
430  * @brief A class to execute callbacks connected to it, with provision
431  * for automatic disconnection.
432  * @sa SafeEmitterArg Releaser
433  * @sa emitter.h
434  * @sa Callback namespace
435  *
436  * Callable objects (such as lambda expressions or the return value of
437  * std::bind) or Callback::FunctorArg objects may be connected to
438  * Emitter classes, and will be executed when EmitterArg::emit() or
439  * EmitterArg::operator()() are called.
440  *
441  * One version of the connect() method takes a Releaser object as an
442  * argument. Such a Releaser object should be a public member of any
443  * target class which wants functors representing (or calling into)
444  * any of its methods to be disconnected automatically from the
445  * EmitterArg object when the target class object is destroyed.
446  *
447  * A connection may be explicitly disconnected by calling the
448  * disconnect() method, and may also be temporarily blocked and
449  * subsequently unblocked with the block() and unblock() methods.
450  *
451  * The template types are the types of the unbound arguments, if any.
452  * EmitterArg<> is typedef'ed to Emitter.
453  *
454  * @b Usage
455  *
456  * These are examples:
457  *
458  * @code
459  * using namespace Cgu;
460  *
461  * Emitter e1;
462  * e1.connect([] () {std::cout << "Hello world\n";});
463  * e1();
464  *
465  * int res;
466  * EmitterArg<int, int&> e2;
467  * e2.connect([] (int i, int& j) {j = 10 * i;});
468  * e2(2, res);
469  * std::cout << "10 times 2 is " << res << '\n';
470  * @endcode
471  *
472  * Callback::FunctorArg objects may be connected to an emitter, and
473  * the connect() method may be directly initialized with the result of
474  * Callback::make(), Callback::make_ref() or Callback::lambda() and
475  * implicit conversion will take place. Here is an example using
476  * Callback::make_ref(), with a class object my_obj of type MyClass,
477  * with a method void MyClass::my_method(const Something&, int):
478  *
479  * @code
480  * using namespace Cgu;
481  *
482  * Something arg;
483  * EmitterArg<int> e;
484  * e.connect(Callback::make_ref(my_obj, &MyClass::my_method, arg));
485  * e(5);
486  * @endcode
487  *
488  * For further background, including about thread-safety and exception
489  * safety and other matters, read this: emitter.h, or for more
490  * information about bound and unbound arguments, read this:
491  * Cgu::Callback.
492  */
493 
494 template <class... FreeArgs>
495 class EmitterArg {
496 
497 #ifndef DOXYGEN_PARSING
498  // f1 is the functor we execute when we emit()
499  // f2 is the functor we execute in our destructor if we are destroyed
500  // before the remote object is
501  struct ListItem {
502  Callback::FunctorArg<FreeArgs...> f1;
504  bool blocked;
505  ListItem(Callback::FunctorArg<FreeArgs...> f1_, Callback::Functor f2_):
506  f1(f1_), f2(f2_), blocked(false) {}
507  };
508 #endif
509 
510  std::list<ListItem> emission_list;
511 
512  // only Releaser objects can access this
513  void tracking_disconnect(const Callback::FunctorArg<FreeArgs...>&);
514 
515 public:
516  friend class Releaser;
517 
518 /**
519  * This will execute the connected functors.
520  * @param args The unbound arguments to be passed to the referenced
521  * function or class method, if any.
522  * @exception std::bad_alloc The method might throw std::bad_alloc if
523  * memory is exhausted and the system throws in that case. In
524  * addition, it will throw if the functions or class methods
525  * referenced by the functors throw (or if the copy constructor of a
526  * free or bound argument throws and it is not a reference argument).
527  */
528  void operator()(typename Cgu::Param<FreeArgs>::ParamType... args) const {emit(args...);}
529 
530 /**
531  * This will execute the connected functors.
532  * @param args The unbound arguments to be passed to the referenced
533  * function or class method, if any.
534  * @exception std::bad_alloc The method might throw std::bad_alloc if
535  * memory is exhausted and the system throws in that case. In
536  * addition, it will throw if the functions or class methods
537  * referenced by the functors throw (or if the copy constructor of a
538  * free or bound argument throws and it is not a reference argument).
539  */
540  void emit(typename Cgu::Param<FreeArgs>::ParamType... args) const;
541 
542 /**
543  * This will execute the connected functors, but it also reports
544  * whether in fact there were any connected functors to execute. (It
545  * is not necessary to use this function just because it is not known
546  * whether a functor is connected - if the standard emit() function is
547  * called when no functor is connected, nothing will happen. The
548  * feature of this method is that it will report the outcome.)
549  * @param args The unbound arguments to be passed to the connected
550  * functions or class methods, if any.
551  * @return Returns false if there were no functors to execute, or true
552  * if functors have been executed.
553  * @exception std::bad_alloc The method might throw std::bad_alloc if
554  * memory is exhausted and the system throws in that case. In
555  * addition, it will throw if the functions or class methods
556  * referenced by the functors throw (or if the copy constructor of a
557  * free or bound argument throws and it is not a reference argument).
558  */
559  bool test_emit(typename Cgu::Param<FreeArgs>::ParamType... args) const;
560 
561 /**
562  * Connects a Callback::FunctorArg object.
563  * @param f The Callback::FunctorArg object to connect.
564  * @return The Callback::FunctorArg object connected.
565  * @exception std::bad_alloc The method might throw std::bad_alloc if
566  * memory is exhausted and the system throws in that case.
567  */
569 
570 /**
571  * Connects a Callback::FunctorArg object.
572  * @param f The Callback::FunctorArg object to connect.
573  * @param r A Releaser object for automatic disconnection of the
574  * Callback::FunctorArg object if the object whose method it
575  * represents is destroyed.
576  * @return The Callback::FunctorArg object connected.
577  * @exception std::bad_alloc The method might throw std::bad_alloc if
578  * memory is exhausted and the system throws in that case.
579  */
581 
582 /**
583  * Connects a callable object, such as formed by a lambda expression
584  * or the result of std::bind.
585  * @param f The callable object to connect. If must have the same
586  * unbound argument types as the EmitterArg object concerned.
587  * @return A Callback::FunctorArg object which can be passed to
588  * disconnect(), block() or unblock().
589  * @exception std::bad_alloc The method might throw std::bad_alloc if
590  * memory is exhausted and the system throws in that case. If might
591  * also throw if the copy or move constructor of the callable object
592  * throws.
593  *
594  * Since 2.1.0
595  */
596 // we need to use enable_if so that where this function is passed a
597 // Callback::SafeFunctorArg object or a pointer to a
598 // Callback::Callback object or some other convertible object, this
599 // templated overload is dropped from the overload set, in order to
600 // support the deprecated overloads of this function.. This overload
601 // calls into the version of this function taking a
602 // Callback::Functor object in order to perform type erasure.
603  template <class F,
604  class = typename std::enable_if<!std::is_convertible<typename std::remove_reference<F>::type,
605  const Callback::FunctorArg<FreeArgs...>>::value>::type>
606  Callback::FunctorArg<FreeArgs...> connect(F&& f) {
607  return connect(Callback::lambda<FreeArgs...>(std::forward<F>(f)));
608  }
609 
610 /**
611  * Connects a callable object, such as formed by a lambda expression
612  * or the result of std::bind.
613  * @param f The callable object to connect. If must have the same
614  * unbound argument types as the EmitterArg object concerned.
615  * @param r A Releaser object for automatic disconnection of the
616  * callable object if an object whose method it represents or calls
617  * into is destroyed.
618  * @return A Callback::FunctorArg object which can be passed to
619  * disconnect(), block() or unblock().
620  * @exception std::bad_alloc The method might throw std::bad_alloc if
621  * memory is exhausted and the system throws in that case. If might
622  * also throw if the copy or move constructor of the callable object
623  * throws.
624  *
625  * Since 2.1.0
626  */
627 // we need to use enable_if so that where this function is passed a
628 // Callback::SafeFunctorArg object or a pointer to a
629 // Callback::Callback object or some other convertible object, this
630 // templated overload is dropped from the overload set, in order to
631 // support the deprecated overloads of this function.. This overload
632 // calls into the version of this function taking a
633 // Callback::Functor object in order to perform type erasure.
634  template <class F,
635  class = typename std::enable_if<!std::is_convertible<typename std::remove_reference<F>::type,
636  const Callback::FunctorArg<FreeArgs...>>::value>::type>
637  Callback::FunctorArg<FreeArgs...> connect(F&& f, Releaser& r) {
638  return connect(Callback::lambda<FreeArgs...>(std::forward<F>(f)), r);
639  }
640 
641 /**
642  * Disconnects a functor previously connected. This does not throw
643  * provided that the destructors of any bound arguments do not throw
644  * (as they should not do), and assuming that merely iterating through
645  * a list does not throw (as it would not on any sane implementation).
646  * @param f The functor to disconnect.
647  * @note If the same functor has been connected more than once to the
648  * same EmitterArg object, this call will disconnect all of them.
649  */
651 
652 /**
653  * Blocks a connected functor from executing when emit() or
654  * operator()() is called until unblock() is called. This method does
655  * not throw (assuming that merely iterating through a list does not
656  * throw, as it would not on any sane implementation).
657  * @param f The functor to block.
658  * @note If the same functor has been connected more than once to the
659  * same EmitterArg object, this call will block all of them.
660  */
662 
663 /**
664  * Unblocks a previously blocked functor. This method does not throw
665  * (assuming that merely iterating through a list does not throw, as
666  * it would not on any sane implementation).
667  * @param f The functor to unblock.
668  * @note If the same functor has been connected more than once to the
669  * same EmitterArg object, this call will unblock all of them.
670  */
672 
673 /**
674  * @exception std::bad_alloc The constructor might throw
675  * std::bad_alloc if memory is exhausted and the system throws in that
676  * case.
677  */
678  EmitterArg() = default;
679 
680 /**
681  * This class cannot be copied. The copy constructor is deleted.
682  */
683  EmitterArg(const EmitterArg&) = delete;
684 
685 /**
686  * This class cannot be copied. The assignment operator is deleted.
687  */
688  EmitterArg& operator=(const EmitterArg&) = delete;
689 
690 /**
691  * The destructor does not throw provided that the destructors of any
692  * bound arguments do not throw (as they should not do), and assuming
693  * that merely iterating through a list does not throw (as it would
694  * not on any sane implementation).
695  */
696  ~EmitterArg();
697 
698 /* Only has effect if --with-glib-memory-slices-compat or
699  * --with-glib-memory-slices-no-compat option picked */
701 };
702 
703 template <class... FreeArgs>
705  for(const auto& l: emission_list) {l.f2();}
706 }
707 
708 template <class... FreeArgs>
710 
711  // create a local copy of emission_list, to enable a connected
712  // function (i) to delete the EmitterArg<> object to which it is
713  // connected, even if there are other functors still to execute in
714  // the same emission (which will execute normally provided they do
715  // not try to call any of the emitter's functions), (ii) to call
716  // 'delete this' nothwithstanding that the connected function is
717  // protected by a Releaser object (assuming all the other restraints
718  // on calling 'delete this' are met), provided that no other access
719  // would be made to the deleted object in a function call connected
720  // to the same emitter which is due to execute subsequently in the
721  // same emission, and (iii) to disconnect itself from the
722  // EmitterArg object. This design approach has a trade-off: if a
723  // connected function tries to block, unblock or disconnect another
724  // function connected to the same EmitterArg<> object which is due
725  // to execute subsequently in the same emission (or to block,
726  // unblock or disconnect itself when it is due to execute again
727  // subsequently in the same emission), the attempted block, unblock
728  // or disconnection will not have any effect on that emission (it
729  // will only have effect on a subsequent emission). In addition, a
730  // connected function may not destroy an object whose non-static
731  // method is connected to the same emitter and which would execute
732  // subsequently in the same emission, even if that object is
733  // protected by a Releaser object (the non-static method will
734  // unsuccessfully attempt to execute notwithstanding the destruction
735  // of the object it would be operating on).
736 
737  // we can't use uniform initialisation here as it would be
738  // construed as invoking an initialiser list with a list item,
739  // rather than passing an already formed list
740  std::list<ListItem> local_list = emission_list;
741 
742  for (const auto& l: local_list) {
743  if (!l.blocked) l.f1(args...);
744  }
745 }
746 
747 template <class... FreeArgs>
749  if (emission_list.empty()) return false;
750  emit(args...);
751  return true;
752 }
753 
754 template <class... FreeArgs>
756  emission_list.emplace_back(f1, Callback::Functor());
757  return f1;
758 }
759 
760 template <class... FreeArgs>
762  // In this method:
763  // f1 is the functor we execute when we emit()
764  // f2 is the functor we execute in our destructor if we are destroyed before the
765  // remote object is
766  // f3 is the functor the remote object executes in its Releaser if it is destroyed
767  // before we are, or if Releaser::operator=() is called
768 
770  Callback::Functor f2{Callback::make_ref(r, &Releaser::remove, f3)};
771  r.add(f3);
772  try {
773  emission_list.emplace_back(f1, f2);
774  }
775  catch (...) {
776  r.remove(f3);
777  throw;
778  }
779  return f1;
780 }
781 
782 template <class... FreeArgs>
784  // in theory, we could have connected the same functor object
785  // more than once, so cater for that
786  auto iter = emission_list.begin();
787  for (;;) {
788  iter = std::find_if(iter, emission_list.end(),
789  [&arg](const ListItem& p) -> bool {return p.f1 == arg;});
790  if (iter != emission_list.end()) {
791  // remove ourselves from the remote Releaser object
792  (iter->f2)();
793 
794  // remove this item from emission_list
795  iter = emission_list.erase(iter);
796  }
797  else break;
798  }
799 }
800 
801 // tracking disconnect() is the same as disconnect(), except that we do not
802 // execute f2 as the remote Releaser object will destroy its own functors
803 // in that case
804 template <class... FreeArgs>
806  auto iter = emission_list.begin();
807  for (;;) {
808  iter = std::find_if(iter, emission_list.end(),
809  [&arg](const ListItem& p) -> bool {return p.f1 == arg;});
810  if (iter != emission_list.end()) {
811  // remove this item from emission_list
812  iter = emission_list.erase(iter);
813  }
814  else break;
815  }
816 }
817 
818 template <class... FreeArgs>
820  // in theory, we could have connected the same functor object
821  // more than once, so cater for that
822  auto iter = emission_list.begin();
823  for (;;) {
824  iter = std::find_if(iter, emission_list.end(),
825  [&arg](const ListItem& p) -> bool {return p.f1 == arg;});
826  if (iter != emission_list.end()) {
827  iter->blocked = true;
828  ++iter;
829  }
830  else break;
831  }
832 }
833 
834 template <class... FreeArgs>
836  // in theory, we could have connected the same functor object
837  // more than once, so cater for that
838  auto iter = emission_list.begin();
839  for (;;) {
840  iter = std::find_if(iter, emission_list.end(),
841  [&arg](const ListItem& p) -> bool {return p.f1 == arg;});
842  if (iter != emission_list.end()) {
843  iter->blocked = false;
844  ++iter;
845  }
846  else break;
847  }
848 }
849 
850 /**
851  * @class SafeEmitterArg emitter.h c++-gtk-utils/emitter.h
852  * @brief A thread-safe class to execute callbacks connected to it,
853  * with provision for automatic disconnection.
854  * @sa EmitterArg Releaser
855  * @sa emitter.h
856  * @sa Callback namespace
857  *
858  * This is a thread-safe version of the EmitterArg class. Callable
859  * objects (such as lambda expressions or the return value of
860  * std::bind) or Callback::SafeFunctorArg objects may be connected to
861  * SafeEmitter classes (referred to be below as "connected
862  * callables"), and will be executed when SafeEmitterArg::emit() or
863  * SafeEmitterArg::operator()() are called.
864  *
865  * One version of the connect() method takes a Releaser object as an
866  * argument. Such a Releaser object should be a public member of any
867  * target class which wants connected callables representing (or
868  * calling into) any of its methods to be disconnected automatically
869  * from the SafeEmitterArg object when the target class object is
870  * destroyed.
871  *
872  * A connection may be explicitly disconnected by calling the
873  * disconnect() method, and may also be temporarily blocked and
874  * subsequently unblocked with the block() and unblock() methods.
875  *
876  * The template types are the types of the unbound arguments, if any.
877  * SafeEmitterArg<> is typedef'ed to SafeEmitter.
878  *
879  * @b Usage
880  *
881  * These are examples:
882  *
883  * @code
884  * using namespace Cgu;
885  *
886  * SafeEmitter se1;
887  * se1.connect([] () {std::cout << "Hello world\n";});
888  * se1();
889  *
890  * int res;
891  * SafeEmitterArg<int, int&> se2;
892  * se2.connect([] (int i, int& j) {j = 10 * i;});
893  * se2(2, res);
894  * std::cout << "10 times 2 is " << res << '\n';
895  * @endcode
896  *
897  * Callback::SafeFunctorArg objects may be connected to an emitter,
898  * and the connect() method may be directly initialized with the
899  * result of Callback::make(), Callback::make_ref() or
900  * Callback::lambda() and implicit conversion will take place. Here
901  * is an example using Callback::make_ref(), with a class object
902  * my_obj of type MyClass, with a method void MyClass::my_method(const
903  * Something&, int):
904  *
905  * @code
906  * using namespace Cgu;
907  *
908  * Something arg;
909  * SafeEmitterArg<int> se;
910  * se.connect(Callback::make_ref(my_obj, &MyClass::my_method, arg));
911  * se(5);
912  * @endcode
913  *
914  * For further background, including about thread-safety and exception
915  * safety and other matters, read this: emitter.h, or for more
916  * information about bound and unbound arguments, read this:
917  * Cgu::Callback.
918  */
919 
920 template <class... FreeArgs>
921 class SafeEmitterArg {
922 
923 #ifndef DOXYGEN_PARSING
924  // f1 is the functor we execute when we emit()
925  // f2 is the functor we execute in our destructor if we are destroyed
926  // before the remote object is
927  struct ListItem {
928  Callback::SafeFunctorArg<FreeArgs...> f1;
930  bool blocked;
932  f1(f1_), f2(f2_), blocked(false) {}
933  };
934 #endif
935 
936  std::list<ListItem> emission_list;
937  mutable Thread::Mutex mutex; // make this mutable so we can lock/unlock in const methods
938 
939  // only Releaser objects can access this
940  void tracking_disconnect(const Callback::SafeFunctorArg<FreeArgs...>&);
941 
942 public:
943  friend class Releaser;
944 
945 /**
946  * This will execute the connected functors. It is thread safe if the
947  * functions or class methods referenced by the connected functors are
948  * thread safe.
949  * @param args The unbound arguments to be passed to the referenced
950  * function or class method, if any.
951  * @exception std::bad_alloc The method might throw std::bad_alloc if
952  * memory is exhausted and the system throws in that case. In
953  * addition, it will throw if the functions or class methods
954  * referenced by the functors throw (or if the copy constructor of a
955  * free or bound argument throws and it is not a reference argument).
956  */
957  void operator()(typename Cgu::Param<FreeArgs>::ParamType... args) const {emit(args...);}
958 
959 /**
960  * This will execute the connected functors. It is thread safe if the
961  * functions or class methods referenced by the connected functors are
962  * thread safe.
963  * @param args The unbound arguments to be passed to the referenced
964  * function or class method, if any.
965  * @exception std::bad_alloc The method might throw std::bad_alloc if
966  * memory is exhausted and the system throws in that case. In
967  * addition, it will throw if the functions or class methods
968  * referenced by the functors throw (or if the copy constructor of a
969  * free or bound argument throws and it is not a reference argument).
970  */
971  void emit(typename Cgu::Param<FreeArgs>::ParamType... args) const;
972 
973 /**
974  * This will execute the connected functors, but it also reports
975  * whether in fact there were any connected functors to execute. It
976  * is thread safe if the functions or class methods referenced by the
977  * connected functors are thread safe. (It is not necessary to use
978  * this function just because it is not known whether a functor is
979  * connected - if the standard emit() function is called when no
980  * functor is connected, nothing will happen. The feature of this
981  * method is that it will report the outcome.)
982  * @param args The unbound arguments to be passed to the referenced
983  * function or class method, if any.
984  * @return Returns false if there were no functors to execute, or true
985  * if functors have been executed.
986  * @exception std::bad_alloc The method might throw std::bad_alloc if
987  * memory is exhausted and the system throws in that case. In
988  * addition, it will throw if the functions or class methods
989  * referenced by the functors throw (or if the copy constructor of a
990  * free or bound argument throws and it is not a reference argument).
991  */
992  bool test_emit(typename Cgu::Param<FreeArgs>::ParamType... args) const;
993 
994 /**
995  * Connects a Callback::SafeFunctorArg object.
996  * @param f The Callback::SafeFunctorArg object to connect.
997  * @return The Callback::SafeFunctorArg object connected.
998  * @exception std::bad_alloc The method might throw std::bad_alloc if
999  * memory is exhausted and the system throws in that case.
1000  */
1002 
1003 /**
1004  * Connects a Callback::SafeFunctorArg object.
1005  * @param f The Callback::SafeFunctorArg object to connect.
1006  * @param r A Releaser object for automatic disconnection of the
1007  * Callback::SafeFunctorArg object if the object whose method it
1008  * represents is destroyed.
1009  * @return The Callback::SafeFunctorArg object connected.
1010  * @exception std::bad_alloc The method might throw std::bad_alloc if
1011  * memory is exhausted and the system throws in that case.
1012  */
1014 
1015 /**
1016  * Connects a callable object, such as formed by a lambda expression
1017  * or the result of std::bind.
1018  * @param f The callable object to connect. If must have the same
1019  * unbound argument types as the SafeEmitterArg object concerned.
1020  * @return A Callback::SafeFunctorArg object which can be passed to
1021  * disconnect(), block() or unblock().
1022  * @exception std::bad_alloc The method might throw std::bad_alloc if
1023  * memory is exhausted and the system throws in that case. If might
1024  * also throw if the copy or move constructor of the callable object
1025  * throws.
1026  *
1027  * Since 2.1.0
1028  */
1029 // we need to use enable_if so that where this function is passed a
1030 // Callback::SafeFunctorArg object or a pointer to a
1031 // Callback::Callback object or some other convertible object, this
1032 // templated overload is dropped from the overload set, in order to
1033 // support the Callback::SafeFunctorArg overloads of this function.
1034 // This overload calls into the version of this function taking a
1035 // Callback::SafeFunctor object in order to perform type erasure.
1036  template <class F,
1037  class = typename std::enable_if<!std::is_convertible<typename std::remove_reference<F>::type,
1038  const Callback::SafeFunctorArg<FreeArgs...>>::value>::type>
1039  Callback::SafeFunctorArg<FreeArgs...> connect(F&& f) {
1040  return connect(Callback::lambda<FreeArgs...>(std::forward<F>(f)));
1041  }
1042 
1043 /**
1044  * Connects a callable object, such as formed by a lambda expression
1045  * or the result of std::bind.
1046  * @param f The callable object to connect. If must have the same
1047  * unbound argument types as the SafeEmitterArg object concerned.
1048  * @param r A Releaser object for automatic disconnection of the
1049  * callable object if an object whose method it represents or calls
1050  * into is destroyed.
1051  * @return A Callback::SafeFunctorArg object which can be passed to
1052  * disconnect(), block() or unblock().
1053  * @exception std::bad_alloc The method might throw std::bad_alloc if
1054  * memory is exhausted and the system throws in that case. If might
1055  * also throw if the copy or move constructor of the callable object
1056  * throws.
1057  *
1058  * Since 2.1.0
1059  */
1060 // we need to use enable_if so that where this function is passed a
1061 // Callback::SafeFunctorArg object or a pointer to a
1062 // Callback::Callback object or some other convertible object, this
1063 // templated overload is dropped from the overload set, in order to
1064 // support the Callback::SafeFunctorArg overloads of this function.
1065 // This overload calls into the version of this function taking a
1066 // Callback::SafeFunctor object in order to perform type erasure.
1067  template <class F,
1068  class = typename std::enable_if<!std::is_convertible<typename std::remove_reference<F>::type,
1069  const Callback::SafeFunctorArg<FreeArgs...>>::value>::type>
1070  Callback::SafeFunctorArg<FreeArgs...> connect(F&& f, Releaser& r) {
1071  return connect(Callback::lambda<FreeArgs...>(std::forward<F>(f)), r);
1072  }
1073 
1074 /**
1075  * Disconnects a functor previously connected. This does not throw
1076  * provided that the destructors of any bound arguments do not throw
1077  * (as they should not do), and assuming that merely iterating through
1078  * a list does not throw (as it would not on any sane implementation).
1079  * It is thread safe.
1080  * @param f The functor to disconnect.
1081  * @note If the same functor has been connected more than once to the
1082  * same SafeEmitterArg object, this call will disconnect all of them.
1083  */
1085 
1086 /**
1087  * Blocks a connected functor from executing when emit() or
1088  * operator()() is called until unblock() is called. This method does
1089  * not throw (assuming that merely iterating through a list does not
1090  * throw, as it would not on any sane implementation). It is thread
1091  * safe.
1092  * @param f The functor to block.
1093  * @note If the same functor has been connected more than once to the
1094  * same SafeEmitterArg object, this call will block all of them.
1095  */
1097 
1098 /**
1099  * Unblocks a previously blocked functor. This method does not throw
1100  * (assuming that merely iterating through a list does not throw, as
1101  * it would not on any sane implementation). It is thread safe.
1102  * @param f The functor to unblock.
1103  * @note If the same functor has been connected more than once to the
1104  * same SafeEmitterArg object, this call will unblock all of them.
1105  */
1107 
1108 /**
1109  * @exception std::bad_alloc The constructor might throw
1110  * std::bad_alloc if memory is exhausted and the system throws in that
1111  * case.
1112  * @exception Thread::MutexError The constructor might throw
1113  * Thread::MutexError if initialisation of the contained mutex fails.
1114  * (It is often not worth checking for this, as it means either memory
1115  * is exhausted or pthread has run out of other resources to create
1116  * new mutexes.)
1117  */
1118  SafeEmitterArg() = default;
1119 
1120 /**
1121  * This class cannot be copied. The copy constructor is deleted.
1122  */
1123  SafeEmitterArg(const SafeEmitterArg&) = delete;
1124 
1125 /**
1126  * This class cannot be copied. The assignment operator is deleted.
1127  */
1128  SafeEmitterArg& operator=(const SafeEmitterArg&) = delete;
1129 
1130 /**
1131  * The destructor does not throw provided that the destructors of any
1132  * bound arguments do not throw (as they should not do), and assuming
1133  * that merely iterating through a list does not throw (as it would
1134  * not on any sane implementation). It is thread-safe as regards the
1135  * dropping of any connected functors and of any relevant Releaser
1136  * objects.
1137  */
1138  ~SafeEmitterArg();
1139 
1140 /* Only has effect if --with-glib-memory-slices-compat or
1141  * --with-glib-memory-slices-no-compat option picked */
1143 };
1144 
1145 template <class... FreeArgs>
1147 
1148  // go through emission_list() item by item, popping off the front and erasing
1149  // as we go in case Releaser::try_remove() fails to acquire the lock on one
1150  // of the iterations
1151  Thread::Mutex::Lock lock{mutex};
1152  while (!emission_list.empty()) {
1153  auto iter = emission_list.begin();
1154  int result = 0; // f2 might be a no-op
1155  // remove ourselves from the remote Releaser object
1156  (iter->f2)(&result);
1157  if (!result) { // we got the Releaser mutex lock or no-op
1158  // now remove this item from emission_list
1159  emission_list.erase(iter);
1160  }
1161  else {
1162  mutex.unlock();
1163  // spin nicely
1164 #ifdef CGU_USE_SCHED_YIELD
1165  sched_yield();
1166 #else
1167  usleep(10);
1168 #endif
1169  mutex.lock();
1170  }
1171  }
1172 }
1173 
1174 template <class... FreeArgs>
1176 
1177  // create a local copy of emission_list, to enable a connected
1178  // function (i) to delete the EmitterArg<> object to which it is
1179  // connected, even if there are other functors still to execute in
1180  // the same emission (which will execute normally provided they do
1181  // not try to call any of the emitter's functions), (ii) to call
1182  // 'delete this' nothwithstanding that the connected function is
1183  // protected by a Releaser object (assuming all the other restraints
1184  // on calling 'delete this' are met), provided that no other access
1185  // would be made to the deleted object in a function call connected
1186  // to the same emitter which is due to execute subsequently in the
1187  // same emission, and (iii) to disconnect itself from the
1188  // EmitterArg<> object. This design approach has a trade-off: if a
1189  // connected function tries to block, unblock or disconnect another
1190  // function connected to the same EmitterArg<> object which is due
1191  // to execute subsequently in the same emission (or to block,
1192  // unblock or disconnect itself when it is due to execute again
1193  // subsequently in the same emission), the attempted block, unblock
1194  // or disconnection will not have any effect on that emission (it
1195  // will only have effect on a subsequent emission). In addition, a
1196  // connected function may not destroy an object whose non-static
1197  // method is connected to the same emitter and which would execute
1198  // subsequently in the same emission, even if that object is
1199  // protected by a Releaser object (the non-static method will
1200  // unsuccessfully attempt to execute notwithstanding the destruction
1201  // of the object it would be operating on).
1202 
1203  // SafeFunctorArg usage has the additional point that while an
1204  // emission is in course, another thread should not try to do any of
1205  // those things, or the same outcome will result. Another thread
1206  // should leave alone objects connected to a SafeEmitterArg<> object
1207  // from the time of operator()() or emit() beginning to the time of
1208  // it ending, and not try to interfere.
1209 
1210  // a side effect of having a local list is that, as required, we
1211  // will not be holding our mutex when executing the functors it
1212  // contains. It is OK having the functors in two different lists
1213  // which are potentially (when our mutex is released) in two
1214  // different threads, because the functors hold their
1215  // Callback::Callback objects by SharedLockPtr so their reference
1216  // count is protected (they are SafeFunctorArg<> functors).
1217 
1218  // we could reduce contention on the mutex by allocating local_list
1219  // outside the mutex, eg by taking the size of emission_list within
1220  // the mutex, then allocating the nodes of local_list outside the
1221  // mutex with that size, and then copying items across within the
1222  // mutex (checking the end iterators of both containers when
1223  // iterating because the size of emitter_list could have changed
1224  // while allocating local_list) and, if the size of emission list
1225  // did change by another thread disconnecting a functor in the
1226  // interval when local_list was allocated, resizing local_list
1227  // downwards with std::list::resize(). However this is mostly
1228  // pointless, because although this arrangement would be as equally
1229  // thread-safe as the implementation below and lessen contention,
1230  // since you don't know exactly what functors will be executed
1231  // anyway if functors are added or removed by one thread while
1232  // another is emitting, such concurrent emitting is not a practice
1233  // to make special provision for. Accordingly, we go the simpler,
1234  // more naive route below.
1235 
1236  std::list<ListItem> local_list;
1237  { // scope block for mutex lock
1238  Thread::Mutex::Lock lock{mutex};
1239  local_list = emission_list;
1240  }
1241 
1242  for (const auto& l: local_list) {
1243  if (!l.blocked) l.f1(args...);
1244  }
1245 }
1246 
1247 template <class... FreeArgs>
1249 
1250  std::list<ListItem> local_list;
1251  { // scope block for mutex lock
1252  Thread::Mutex::Lock lock{mutex};
1253  if (emission_list.empty()) return false;
1254  local_list = emission_list;
1255  }
1256 
1257  for (const auto& l: local_list) {
1258  if (!l.blocked) l.f1(args...);
1259  }
1260  return true;
1261 }
1262 
1263 template <class... FreeArgs>
1265  // construct the new node outside the mutex to reduce contention and
1266  // then splice it at the end
1267  std::list<ListItem> tmp{ListItem{f1, Callback::SafeFunctorArg<int*>()}};
1268  Thread::Mutex::Lock lock{mutex};
1269  emission_list.splice(emission_list.end(), std::move(tmp));
1270  return f1;
1271 }
1272 
1273 template <class... FreeArgs>
1275  // In this method:
1276  // f1 is the functor we execute when we emit()
1277  // f2 is the functor we execute in our destructor if we are destroyed before the
1278  // remote object is
1279  // f3 is the functor the remote object executes in its Releaser if it is destroyed
1280  // before we are, or if Releaser::operator=() is called
1281 
1283  Callback::SafeFunctorArg<int*> f2{Callback::make_ref(r, &Releaser::try_remove, f3)};
1284  // we can't call Releaser::add() when holding our mutex or we will
1285  // get out of order locking, as Releaser's mutex is acquired in that
1286  // method, and we don't need to do so
1287  r.add(f3);
1288  try {
1289  // construct the new node outside the mutex to reduce contention
1290  // and then splice it at the end
1291  std::list<ListItem> tmp{ListItem{f1, f2}};
1292  Thread::Mutex::Lock lock{mutex};
1293  emission_list.splice(emission_list.end(), std::move(tmp));
1294  }
1295  catch (...) {
1296  r.remove(f3);
1297  throw;
1298  }
1299  return f1;
1300 }
1301 
1302 template <class... FreeArgs>
1304  // in theory, we could have connected the same functor object more than
1305  // once, so cater for that as well as Releaser::try_remove() failing
1306  Thread::Mutex::Lock lock{mutex};
1307  auto iter = emission_list.begin();
1308  for(;;) {
1309  // gcc-4.4 doesn't support lambdas:
1310  iter = std::find_if(iter, emission_list.end(),
1311  [&arg](const ListItem& p) -> bool {return p.f1 == arg;});
1312  if (iter != emission_list.end()) {
1313  int result = 0; // f2 might be a no-op
1314  // remove ourselves from the remote Releaser object
1315  (iter->f2)(&result);
1316  if (!result) { // we got the Releaser mutex lock or no-op
1317  // now remove this item from emission_list
1318  iter = emission_list.erase(iter);
1319  }
1320  else {
1321  mutex.unlock();
1322  // spin nicely
1323 #ifdef CGU_USE_SCHED_YIELD
1324  sched_yield();
1325 #else
1326  usleep(10);
1327 #endif
1328  mutex.lock();
1329  // start again at the beginning - we have released the mutex
1330  // so our iterator may have become invalid
1331  iter = emission_list.begin();
1332  }
1333  }
1334  else break;
1335  }
1336 }
1337 
1338 // tracking disconnect() is the same as disconnect(), except that we do not
1339 // execute f2 as the remote Releaser object will destroy its own functors
1340 // in that case
1341 template <class... FreeArgs>
1343  Thread::Mutex::Lock lock{mutex};
1344  auto iter = emission_list.begin();
1345  for (;;) {
1346  iter = std::find_if(iter, emission_list.end(),
1347  [&arg](const ListItem& p) -> bool {return p.f1 == arg;});
1348  if (iter != emission_list.end()) {
1349  // remove this item from emission_list
1350  iter = emission_list.erase(iter);
1351  }
1352  else break;
1353  }
1354 }
1355 
1356 template <class... FreeArgs>
1358  // in theory, we could have connected the same functor object
1359  // more than once, so cater for that
1360  Thread::Mutex::Lock lock{mutex};
1361  auto iter = emission_list.begin();
1362  for (;;) {
1363  iter = std::find_if(iter, emission_list.end(),
1364  [&arg](const ListItem& p) -> bool {return p.f1 == arg;});
1365  if (iter != emission_list.end()) {
1366  iter->blocked = true;
1367  ++iter;
1368  }
1369  else break;
1370  }
1371 }
1372 
1373 template <class... FreeArgs>
1375  // in theory, we could have connected the same functor object
1376  // more than once, so cater for that
1377  Thread::Mutex::Lock lock{mutex};
1378  auto iter = emission_list.begin();
1379  for (;;) {
1380  iter = std::find_if(iter, emission_list.end(),
1381  [&arg](const ListItem& p) -> bool {return p.f1 == arg;});
1382  if (iter != emission_list.end()) {
1383  iter->blocked = false;
1384  ++iter;
1385  }
1386  else break;
1387  }
1388 }
1389 
1390 } // namespace Cgu
1391 
1392 #endif // EMITTER_H