ArenaPoolSTLAllocator.h File Reference

STL-style allocator wrapper for ArenaPoolAllocator. More...

#include "AthAllocators/ArenaPoolAllocator.h"
#include "CxxUtils/concepts.h"
#include "CxxUtils/checker_macros.h"
#include <string>
#include <type_traits>
#include "AthAllocators/ArenaPoolSTLAllocator.icc"

Include dependency graph for ArenaPoolSTLAllocator.h:

Go to the source code of this file.

Classes
class	SG::ArenaPoolSTLAllocator_initParams< T >
	Initializer for pool allocator parameters. More...
class	SG::ArenaPoolSTLAllocator< T, VETO >
	STL-style allocator wrapper for ArenaPoolAllocator. More...
struct	SG::ArenaPoolSTLAllocator< T, VETO >::rebind< U >
	Standard STL allocator rebinder. More...
class	SG::ArenaPoolSTLAllocator< T *, VETO >
	STL-style allocator wrapper for ArenaPoolAllocator. More...
struct	SG::ArenaPoolSTLAllocator< T *, VETO >::rebind< U >
	Standard STL allocator rebinder. More...
class	SG::ArenaNonConstPoolSTLAllocator< T >
	Forward declaration. More...
class	SG::ArenaPoolSTLAllocator< T, typename std::enable_if<!std::is_pointer_v< T >, T >::type >
	STL-style allocator wrapper for ArenaPoolAllocator. More...
struct	SG::ArenaPoolSTLAllocator< T, typename std::enable_if<!std::is_pointer_v< T >, T >::type >::rebind< U >
	Standard STL allocator rebinder. More...
class	SG::ArenaNonConstPoolSTLAllocator< T >
	Forward declaration. More...

Namespaces
	SG
	Forward declaration.

Functions
template<class T , class VETO >
void	SG::maybeUnprotect (ArenaPoolSTLAllocator< T, VETO > &a)
	Hook for unprotecting an arena. More...

Detailed Description

STL-style allocator wrapper for ArenaPoolAllocator.

Author

scott snyder

Date

Jul 2008 This class defines a STL-style allocator for types T with the following special properties.

• For non-pointer T's, we use an ArenaPoolAllocator. For pointer T's, we use the standard STL allocator. STL pair<> types will also use the standard STL allocator. Further comments below apply to the first case.
• The memory is owned directly by the allocator object.
• Only one object at a time may be allocated.
• Deallocate doesn't do anything. The only way to release the memory is to delete the allocator.

So, this allocator is suitable for an STL container which allocates lots of fixed-size objects, where the usage pattern is to fill the container up, use it for a while, then delete the container. (The particular scenario that inspired this was the map for NavigationToken.)

Much of the complexity here is due to the fact that the allocator type that gets passed to the container is an allocator for the container's value_type, but that allocator is not actually used to allocate memory. Instead, an allocator for the internal node type is used. This makes it awkward if you want to have allocators that store state. We also need to support hash tables, which make two types of allocation. Nodes are fixed-size and are allocated individually, while the hash table is variable-sized and is of pointer type.

Further, to avoid creating a pool for the allocator for the container's value_type (when the container doesn't actually use that for allocation), this template has a second argument. This defaults to the first argument, but is passed through by rebind. If the first and second argument are the same, then we don't create a pool.

The effect of all this is that you can give an allocator type like ArenaPoolSTLAllocator<Mytype> to a STL container. Allocators for Mytype and Mytype* won't use a pool, but an allocator for node<Mytype> will use the pool.

Definition in file ArenaPoolSTLAllocator.h.