1 /* Copyright (c) 2015. 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 constexpr Extension(std::size_t id) : id_(id) {}
27 constexpr Extension() : id_(INVALID_ID) {}
28 std::size_t id() const { return id_; }
29 bool valid() { 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_;
52 std::vector<void*> extensions_;
54 static size_t extension_create(void (*deleter)(void*))
56 std::size_t res = deleters_.size();
57 deleters_.push_back(deleter);
61 static Extension<T,U> extension_create(void (*deleter)(void*))
63 return Extension<T,U>(extension_create(deleter));
65 template<class U> static
66 Extension<T,U> extension_create()
68 return extension_create([](void* p){ delete static_cast<U*>(p); });
70 Extendable() : extensions_(deleters_.size(), nullptr) {}
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)
81 deleters_[i - 1](extensions_[i - 1]);
84 // Type-unsafe versions of the facet access methods:
85 void* extension(std::size_t rank)
87 if (rank >= extensions_.size())
90 return extensions_.at(rank);
92 void extension_set(std::size_t rank, void* value, bool use_dtor = true)
94 if (rank >= extensions_.size())
95 extensions_.resize(rank + 1, nullptr);
96 void* old_value = this->extension(rank);
97 extensions_.at(rank) = value;
98 if (use_dtor && old_value != nullptr && deleters_[rank])
99 deleters_[rank](old_value);
102 // Type safe versions of the facet access methods:
104 U* extension(Extension<T,U> rank)
106 return static_cast<U*>(extension(rank.id()));
109 void extension_set(Extension<T,U> rank, U* value, bool use_dtor = true)
111 extension_set(rank.id(), value, use_dtor);
114 // Convenience extension access when the type has a associated EXTENSION ID:
115 template<class U> U* extension() { return extension<U>(U::EXTENSION_ID); }
116 template<class U> void extension_set(U* p) { extension_set<U>(U::EXTENSION_ID, p); }
120 std::vector<void(*)(void*)> Extendable<T>::deleters_ = {};