/usr/include/xbt/Extendable.hpp is in libsimgrid-dev 3.18+dfsg-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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* All rights reserved. */
/* This program is free software; you can redistribute it and/or modify it
* under the terms of the license (GNU LGPL) which comes with this package. */
#ifndef SIMGRID_XBT_LIB_HPP
#define SIMGRID_XBT_LIB_HPP
#include <cstddef>
#include <limits>
#include <vector>
namespace simgrid {
namespace xbt {
template<class T, class U> class Extension;
template<class T> class Extendable;
template<class T, class U>
class Extension {
static const std::size_t INVALID_ID = std::numeric_limits<std::size_t>::max();
std::size_t id_;
friend class Extendable<T>;
explicit constexpr Extension(std::size_t id) : id_(id) {}
public:
explicit constexpr Extension() : id_(INVALID_ID) {}
std::size_t id() const { return id_; }
bool valid() { return id_ != INVALID_ID; }
};
/** An Extendable is an object that you can extend with external elements.
*
* 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.
*
* Imagine that you want to write a plugin dealing with the energy in SimGrid.
* You will have to store some information about each and every host.
*
* You could modify the Host class directly (but your code will soon become messy).
* You could create a class EnergyHost deriving Host, but it is not easily combinable
* with a notion of Host extended with another concept (such as mobility).
* You could completely externalize these data with an associative map Host->EnergyHost.
* It would work, provided that you implement this classical feature correctly (and it would induce a little performance penalty).
* Instead, you should add a new extension to the Host class, that happens to be Extendable.
*
*/
template<class T>
class Extendable {
private:
static std::vector<void(*)(void*)> deleters_;
std::vector<void*> extensions_;
public:
static size_t extension_create(void (*deleter)(void*))
{
std::size_t res = deleters_.size();
deleters_.push_back(deleter);
return res;
}
template<class U>
static Extension<T,U> extension_create(void (*deleter)(void*))
{
return Extension<T,U>(extension_create(deleter));
}
template<class U> static
Extension<T,U> extension_create()
{
return Extension<T, U>(extension_create([](void* p) { delete static_cast<U*>(p); }));
}
Extendable() : extensions_(deleters_.size(), nullptr) {}
~Extendable()
{
/* Call destructors in reverse order of their registrations
*
* The rationale for this, is that if an extension B as been added after
* an extension A, the subsystem of B might depend on the subsystem on A and
* an extension of B might need to have the extension of A around when executing
* its cleanup function/destructor. */
for (std::size_t i = extensions_.size(); i > 0; --i)
if (extensions_[i - 1] != nullptr && deleters_[i - 1] != nullptr)
deleters_[i - 1](extensions_[i - 1]);
}
// Type-unsafe versions of the facet access methods:
void* extension(std::size_t rank)
{
if (rank >= extensions_.size())
return nullptr;
else
return extensions_.at(rank);
}
void extension_set(std::size_t rank, void* value, bool use_dtor = true)
{
if (rank >= extensions_.size())
extensions_.resize(rank + 1, nullptr);
void* old_value = this->extension(rank);
extensions_.at(rank) = value;
if (use_dtor && old_value != nullptr && deleters_[rank])
deleters_[rank](old_value);
}
// Type safe versions of the facet access methods:
template<class U>
U* extension(Extension<T,U> rank)
{
return static_cast<U*>(extension(rank.id()));
}
template<class U>
void extension_set(Extension<T,U> rank, U* value, bool use_dtor = true)
{
extension_set(rank.id(), value, use_dtor);
}
// Convenience extension access when the type has a associated EXTENSION ID:
template<class U> U* extension() { return extension<U>(U::EXTENSION_ID); }
template<class U> void extension_set(U* p) { extension_set<U>(U::EXTENSION_ID, p); }
};
template<class T>
std::vector<void(*)(void*)> Extendable<T>::deleters_ = {};
}
}
#endif
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