1 /* Copyright (c) 2015-2019. The SimGrid Team.
2 * All rights reserved. */
4 /* This program is free software; you can redistribute it and/or modify it
5 * under the terms of the license (GNU LGPL) which comes with this package. */
7 #ifndef SIMGRID_XBT_LIB_HPP
8 #define SIMGRID_XBT_LIB_HPP
17 template<class T, class U> class Extension;
18 template<class T> class Extendable;
20 template<class T, class U>
22 static const std::size_t INVALID_ID = std::numeric_limits<std::size_t>::max();
24 friend class Extendable<T>;
25 explicit constexpr Extension(std::size_t id) : id_(id) {}
27 explicit constexpr Extension() : id_(INVALID_ID) {}
28 std::size_t id() const { return id_; }
29 bool valid() const { return id_ != INVALID_ID; }
32 /** An Extendable is an object that you can extend with external elements.
34 * An Extension is one dimension of such extension. They are similar to the concept of mixins, that is, a set of behavior that is injected into a class without derivation.
36 * Imagine that you want to write a plugin dealing with the energy in SimGrid.
37 * You will have to store some information about each and every host.
39 * You could modify the Host class directly (but your code will soon become messy).
40 * You could create a class EnergyHost deriving Host, but it is not easily combinable
41 * with a notion of Host extended with another concept (such as mobility).
42 * You could completely externalize these data with an associative map Host->EnergyHost.
43 * It would work, provided that you implement this classical feature correctly (and it would induce a little performance penalty).
44 * Instead, you should add a new extension to the Host class, that happens to be Extendable.
50 static std::vector<void(*)(void*)> deleters_;
51 std::vector<void*> extensions_;
53 static size_t extension_create(void (*deleter)(void*))
55 deleters_.push_back(deleter);
56 return deleters_.size() - 1;
59 static Extension<T,U> extension_create(void (*deleter)(void*))
61 return Extension<T,U>(extension_create(deleter));
63 template<class U> static
64 Extension<T,U> extension_create()
66 return Extension<T, U>(extension_create([](void* p) { delete static_cast<U*>(p); }));
68 Extendable() : extensions_(deleters_.size(), nullptr) {}
69 Extendable(const Extendable&) = delete;
70 Extendable& operator=(const Extendable&) = delete;
73 /* Call destructors in reverse order of their registrations
75 * The rationale for this, is that if an extension B as been added after
76 * an extension A, the subsystem of B might depend on the subsystem on A and
77 * an extension of B might need to have the extension of A around when executing
78 * its cleanup function/destructor. */
79 for (std::size_t i = extensions_.size(); i > 0; --i)
80 if (extensions_[i - 1] != nullptr && deleters_[i - 1] != nullptr)
81 deleters_[i - 1](extensions_[i - 1]);
84 // Type-unsafe versions of the facet access methods:
85 void* extension(std::size_t rank) const
87 return rank < extensions_.size() ? extensions_[rank] : nullptr;
89 void extension_set(std::size_t rank, void* value, bool use_dtor = true)
91 if (rank >= extensions_.size())
92 extensions_.resize(rank + 1, nullptr);
93 void* old_value = this->extension(rank);
94 extensions_[rank] = value;
95 if (use_dtor && old_value != nullptr && deleters_[rank])
96 deleters_[rank](old_value);
99 // Type safe versions of the facet access methods:
100 template <class U> U* extension(Extension<T, U> rank) const { return static_cast<U*>(extension(rank.id())); }
102 void extension_set(Extension<T,U> rank, U* value, bool use_dtor = true)
104 extension_set(rank.id(), value, use_dtor);
107 // Convenience extension access when the type has a associated EXTENSION ID:
108 template <class U> U* extension() const { return extension<U>(U::EXTENSION_ID); }
109 template<class U> void extension_set(U* p) { extension_set<U>(U::EXTENSION_ID, p); }
112 template <class T> std::vector<void (*)(void*)> Extendable<T>::deleters_;