1 /* Copyright (c) 2015-2020. 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 constexpr std::size_t INVALID_ID = std::numeric_limits<std::size_t>::max();
23 std::size_t id_ = INVALID_ID;
24 friend class Extendable<T>;
25 explicit constexpr Extension(std::size_t id) : id_(id) {}
27 explicit constexpr Extension() = default;
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_{std::max<decltype(deleters_.size())>(1, deleters_.size()), nullptr};
54 static size_t extension_create(void (*deleter)(void*))
56 if (deleters_.empty()) { // Save space for void* user data
57 deleters_.push_back(nullptr);
59 deleters_.push_back(deleter);
60 return deleters_.size() - 1;
63 static Extension<T,U> extension_create(void (*deleter)(void*))
65 return Extension<T,U>(extension_create(deleter));
67 template<class U> static
68 Extension<T,U> extension_create()
70 return Extension<T, U>(extension_create([](void* p) { delete static_cast<U*>(p); }));
72 Extendable() = default;
73 Extendable(const Extendable&) = delete;
74 Extendable& operator=(const Extendable&) = delete;
77 /* Call destructors in reverse order of their registrations
79 * The rationale for this, is that if an extension B as been added after
80 * an extension A, the subsystem of B might depend on the subsystem on A and
81 * an extension of B might need to have the extension of A around when executing
82 * its cleanup function/destructor. */
83 for (std::size_t i = extensions_.size(); i > 1; --i) // rank=0 is the spot of user's void*
84 if (extensions_[i - 1] != nullptr && deleters_[i - 1] != nullptr)
85 deleters_[i - 1](extensions_[i - 1]);
88 // Type-unsafe versions of the facet access methods:
89 void* extension(std::size_t rank) const
91 return rank < extensions_.size() ? extensions_[rank] : nullptr;
93 void extension_set(std::size_t rank, void* value, bool use_dtor = true)
95 if (rank >= extensions_.size())
96 extensions_.resize(rank + 1, nullptr);
97 void* old_value = this->extension(rank);
98 extensions_[rank] = value;
99 if (use_dtor && old_value != nullptr && deleters_[rank])
100 deleters_[rank](old_value);
103 // Type safe versions of the facet access methods:
104 template <class U> U* extension(Extension<T, U> rank) const { return static_cast<U*>(extension(rank.id())); }
106 void extension_set(Extension<T,U> rank, U* value, bool use_dtor = true)
108 extension_set(rank.id(), value, use_dtor);
110 // void* version, for C users and nostalgics
111 void set_data(void* data){
114 void* get_data() const { return extensions_[0]; }
115 // Convenience extension access when the type has a associated EXTENSION ID:
116 template <class U> U* extension() const { return extension<U>(U::EXTENSION_ID); }
117 template<class U> void extension_set(U* p) { extension_set<U>(U::EXTENSION_ID, p); }
120 template <class T> std::vector<void (*)(void*)> Extendable<T>::deleters_;