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 FacetLevel;
18 template<class T> class Facetable;
20 template<class T, class U>
22 static const std::size_t INVALID_ID = std::numeric_limits<std::size_t>::max();
24 friend class Facetable<T>;
25 constexpr FacetLevel(std::size_t id) : id_(id) {}
27 constexpr FacetLevel() : id_(INVALID_ID) {}
28 std::size_t id() const { return id_; }
29 bool valid() { return id_ != INVALID_ID; }
32 /** A Facetable is an object that you can extend with external facets.
34 * Facets 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 facet to the Host class, that happens to be Facetable.
50 static std::vector<void(*)(void*)> deleters_;
52 std::vector<void*> facets_;
54 static size_t add_level(void (*deleter)(void*))
56 std::size_t res = deleters_.size();
57 deleters_.push_back(deleter);
61 static FacetLevel<T,U> add_level(void (*deleter)(void*))
63 return FacetLevel<T,U>(add_level(deleter));
65 template<class U> static
66 FacetLevel<T,U> add_level()
68 return add_level([](void* p){ delete static_cast<U*>(p); });
70 Facetable() : facets_(deleters_.size(), nullptr) {}
73 /* Call destructors in reverse order of their registrations
75 * The rationale for this, is that if a level B as been added after a
76 * facet A, the subsystem of B might depend on the subsystem on A and a
77 * facet of B might need to have the facet of A around when executing
78 * its cleanup function/destructor. */
79 for (std::size_t i = facets_.size(); i > 0; --i)
80 if (facets_[i - 1] != nullptr)
81 deleters_[i - 1](facets_[i - 1]);
84 // Type-unsafe versions of the facet access methods:
85 void* facet(std::size_t level)
87 if (level >= facets_.size())
90 return facets_.at(level);
92 void set_facet(std::size_t level, void* value, bool use_dtor = true)
94 if (level >= facets_.size())
95 facets_.resize(level + 1, nullptr);
96 void* old_value = this->facet(level);
97 facets_.at(level) = value;
98 if (use_dtor && old_value != nullptr && deleters_[level])
99 deleters_[level](old_value);
102 // Type safe versions of the facet access methods:
104 U* facet(FacetLevel<T,U> level)
106 return static_cast<U*>(facet(level.id()));
109 void set_facet(FacetLevel<T,U> level, U* value, bool use_dtor = true)
111 set_facet(level.id(), value, use_dtor);
114 // Convnience facet access when the type has a associated LEVEL:
115 template<class U> U* facet() { return facet<U>(U::LEVEL); }
116 template<class U> void set_facet(U* p) { set_facet<U>(U::LEVEL, p); }
120 std::vector<void(*)(void*)> Facetable<T>::deleters_ = {};