Reference documentation for deal.II version GIT relicensing-662-g00096bcf61 2024-05-18 15:40:02+00:00
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Classes | Public Member Functions | Static Public Member Functions | Private Types | Private Member Functions | Private Attributes | Static Private Attributes | List of all members
VectorMemory< VectorType > Class Template Referenceabstract

#include <deal.II/lac/vector_memory.h>

Inheritance diagram for VectorMemory< VectorType >:
Inheritance graph


class  Pointer

Public Member Functions

virtual ~VectorMemory () override=default
virtual VectorType * alloc ()=0
virtual void free (const VectorType *const)=0
template<class Archive >
void serialize (Archive &ar, const unsigned int version)
Subscriptor functionality

Classes derived from Subscriptor provide a facility to subscribe to this object. This is mostly used by the SmartPointer class.

void subscribe (std::atomic< bool > *const validity, const std::string &identifier="") const
void unsubscribe (std::atomic< bool > *const validity, const std::string &identifier="") const
unsigned int n_subscriptions () const
template<typename StreamType >
void list_subscribers (StreamType &stream) const
void list_subscribers () const

Static Public Member Functions

static ::ExceptionBaseExcNotAllocatedHere ()
static ::ExceptionBaseExcInUse (int arg1, std::string arg2, std::string arg3)
static ::ExceptionBaseExcNoSubscriber (std::string arg1, std::string arg2)

Private Types

using map_value_type = decltype(counter_map)::value_type
using map_iterator = decltype(counter_map)::iterator

Private Member Functions

void check_no_subscribers () const noexcept

Private Attributes

std::atomic< unsigned intcounter
std::map< std::string, unsigned intcounter_map
std::vector< std::atomic< bool > * > validity_pointers
const std::type_info * object_info

Static Private Attributes

static std::mutex mutex

Detailed Description

template<typename VectorType = ::Vector<double>>
class VectorMemory< VectorType >

Memory management base class for vectors. This is an abstract base class used, among other places, by all iterative methods to allocate space for auxiliary vectors.

The purpose of this class is as follows: in iterative solvers and other places, one needs to allocate temporary storage for vectors, for example for auxiliary vectors. One could allocate and release them anew every time, but this may be expensive in some situations if it has to happen very frequently. A common case for this is when an iterative method is used to invert a matrix in each iteration of an outer solver, such as when inverting a matrix block for a Schur complement solver. (step-20 does this, for example, but instead just keeps a vector around permanently for temporary storage.)

In such situations, allocating and deallocating vectors anew in each call to the inner solver is expensive and leads to memory fragmentation. The present class allows to avoid this by offering an interface that other classes can use to allocate and deallocate vectors. Different derived classes then implement different strategies to provide temporary storage vectors to using classes.

For example, the PrimitiveVectorMemory class simply allocates and deallocates vectors via the operating system facilities (i.e., using new and delete) each time it is asked for a vector. It is an appropriate implementation to use for iterative solvers that are called only once, or very infrequently.

On the other hand, the GrowingVectorMemory class never returns memory space to the operating system memory management subsystem during its lifetime; it only marks them as unused and allows them to be reused next time a vector is requested.

Practical use

Classes derived from this base class return pointers to new vectors via the VectorMemory::alloc() function, and re-claim the vector when it is returned via VectorMemory::free(). These two functions therefore play a similar role as new and delete. This includes the usual drawbacks: It is simple to forget to call VectorMemory::free() at the end of a function that uses this facility, or to forget it in an if branch of the function where one has an early return from the function. In both cases, this results in a memory leak: a correct piece of code has to call VectorMemory::free() for all allocated vectors at all possible exit points. This includes places where a function is left because an exception is thrown further down in the call stack and not explicitly handled here.

In other words, vectors allocated via VectorMemory::alloc() have the same issue as raw pointers allocated via new: It is easy to write code that has memory leaks. In the case of raw pointers, the common solution is to use the std::unique_ptr class instead (see In the case of the current class, the VectorMemory::Pointer class is the solution: it is a class that for all practical purposes looks like a pointer, but upon destruction also returns the vector back to the VectorMemory object from which it got it. Since destruction of the VectorMemory::Pointer class happens whenever it goes out of scope (whether because the function explicitly returns, or because control flow leaves it due to an exception), a memory leak cannot happen: the vector the VectroMemory::Pointer object points to is always returned.

Definition at line 104 of file vector_memory.h.

Member Typedef Documentation

◆ map_value_type

using Subscriptor::map_value_type = decltype(counter_map)::value_type

The data type used in counter_map.

Definition at line 229 of file subscriptor.h.

◆ map_iterator

using Subscriptor::map_iterator = decltype(counter_map)::iterator

The iterator type used in counter_map.

Definition at line 234 of file subscriptor.h.

Constructor & Destructor Documentation

◆ ~VectorMemory()

template<typename VectorType = ::Vector<double>>
virtual VectorMemory< VectorType >::~VectorMemory ( )

Virtual destructor. This destructor is declared virtual to allow destroying objects of derived type through pointers to this base class.

Member Function Documentation

◆ alloc()

template<typename VectorType = ::Vector<double>>
virtual VectorType * VectorMemory< VectorType >::alloc ( )
pure virtual

Return a pointer to a new vector. The number of elements or their subdivision into blocks (if applicable) is unspecified and users of this function should reset vectors to their proper size. The same holds for the contents of vectors: they are unspecified. In other words, the place that calls this function will need to resize or reinitialize it appropriately.

Just like using new and delete explicitly in code invites bugs where memory is leaked (either because the corresponding delete is forgotten altogether, or because of exception safety issues), using the alloc() and free() functions explicitly invites writing code that accidentally leaks memory. You should consider using the VectorMemory::Pointer class instead, which provides the same kind of service that std::unique provides for arbitrary memory allocated on the heap.

Implemented in PrimitiveVectorMemory< VectorType >, GrowingVectorMemory< VectorType >, GrowingVectorMemory< BlockVector< number > >, GrowingVectorMemory< Vector< double > >, and GrowingVectorMemory< VectorType >.

◆ free()

template<typename VectorType = ::Vector<double>>
virtual void VectorMemory< VectorType >::free ( const VectorType * const  )
pure virtual

Return a vector and indicate that it is not going to be used any further by the place that called alloc() to get a pointer to it.

Just like using new and delete explicitly in code invites bugs where memory is leaked (either because the corresponding delete is forgotten altogether, or because of exception safety issues), using the alloc() and free() functions explicitly invites writing code that accidentally leaks memory. You should consider using the VectorMemory::Pointer class instead, which provides the same kind of service that std::unique provides for arbitrary memory allocated on the heap.

Implemented in PrimitiveVectorMemory< VectorType >, GrowingVectorMemory< VectorType >, and GrowingVectorMemory< VectorType >.

◆ subscribe()

void Subscriptor::subscribe ( std::atomic< bool > *const  validity,
const std::string &  identifier = "" 
) const

Subscribes a user of the object by storing the pointer validity. The subscriber may be identified by text supplied as identifier.

Definition at line 135 of file

◆ unsubscribe()

void Subscriptor::unsubscribe ( std::atomic< bool > *const  validity,
const std::string &  identifier = "" 
) const

Unsubscribes a user from the object.

The identifier and the validity pointer must be the same as the one supplied to subscribe().

Definition at line 155 of file

◆ n_subscriptions()

unsigned int Subscriptor::n_subscriptions ( ) const

Return the present number of subscriptions to this object. This allows to use this class for reference counted lifetime determination where the last one to unsubscribe also deletes the object.

Definition at line 300 of file subscriptor.h.

◆ list_subscribers() [1/2]

template<typename StreamType >
void Subscriptor::list_subscribers ( StreamType &  stream) const

List the subscribers to the input stream.

Definition at line 317 of file subscriptor.h.

◆ list_subscribers() [2/2]

void Subscriptor::list_subscribers ( ) const

List the subscribers to deallog.

Definition at line 203 of file

◆ serialize()

template<class Archive >
void Subscriptor::serialize ( Archive &  ar,
const unsigned int  version 

Read or write the data of this object to or from a stream for the purpose of serialization using the BOOST serialization library.

This function does not actually serialize any of the member variables of this class. The reason is that what this class stores is only who subscribes to this object, but who does so at the time of storing the contents of this object does not necessarily have anything to do with who subscribes to the object when it is restored. Consequently, we do not want to overwrite the subscribers at the time of restoring, and then there is no reason to write the subscribers out in the first place.

Definition at line 309 of file subscriptor.h.

◆ check_no_subscribers()

void Subscriptor::check_no_subscribers ( ) const

Check that there are no objects subscribing to this object. If this check passes then it is safe to destroy the current object. It this check fails then this function will either abort or print an error message to deallog (by using the AssertNothrow mechanism), but will not throw an exception.

Since this function is just a consistency check it does nothing in release mode.
If this function is called when there is an uncaught exception then, rather than aborting, this function prints an error message to the standard error stream and returns.

Definition at line 52 of file

Member Data Documentation

◆ counter

std::atomic<unsigned int> Subscriptor::counter

Store the number of objects which subscribed to this object. Initially, this number is zero, and upon destruction it shall be zero again (i.e. all objects which subscribed should have unsubscribed again).

The creator (and owner) of an object is counted in the map below if HE manages to supply identification.

We use the mutable keyword in order to allow subscription to constant objects also.

This counter may be read from and written to concurrently in multithreaded code: hence we use the std::atomic class template.

Definition at line 218 of file subscriptor.h.

◆ counter_map

std::map<std::string, unsigned int> Subscriptor::counter_map

In this map, we count subscriptions for each different identification string supplied to subscribe().

Definition at line 224 of file subscriptor.h.

◆ validity_pointers

std::vector<std::atomic<bool> *> Subscriptor::validity_pointers

In this vector, we store pointers to the validity bool in the SmartPointer objects that subscribe to this class.

Definition at line 240 of file subscriptor.h.

◆ object_info

const std::type_info* Subscriptor::object_info

Pointer to the typeinfo object of this object, from which we can later deduce the class name. Since this information on the derived class is neither available in the destructor, nor in the constructor, we obtain it in between and store it here.

Definition at line 248 of file subscriptor.h.

◆ mutex

std::mutex Subscriptor::mutex

A mutex used to ensure data consistency when accessing the mutable members of this class. This lock is used in the subscribe() and unsubscribe() functions, as well as in list_subscribers().

Definition at line 271 of file subscriptor.h.

The documentation for this class was generated from the following file: