OpenVDB  5.2.0
Classes | Public Types | Public Member Functions | Static Public Member Functions | Friends | List of all members
PagedArray< ValueT, Log2PageSize, TableT > Class Template Reference

Concurrent, page-based, dynamically-sized linear data structure with O(1) random access and STL-compliant iterators. It is primarily intended for applications that concurrently insert (a possibly unkown number of) elements into a dynamically growing linear array, and fast random access to said elements. More...

#include <PagedArray.h>

Classes

class  ConstIterator
 
class  Iterator
 
class  Page
 
class  ValueBuffer
 

Public Types

using ValueType = ValueT
 

Public Member Functions

 PagedArray ()=default
 Default constructor. More...
 
 ~PagedArray ()
 Destructor removed all allocated pages. More...
 
 PagedArray (const PagedArray &)=delete
 
PagedArrayoperator= (const PagedArray &)=delete
 
size_t push_back (const ValueType &value)
 Thread safe insertion, adds a new element at the end and increases the container size by one and returns the linear offset for the inserted element. More...
 
size_t push_back_unsafe (const ValueType &value)
 Slightly faster than the thread-safe push_back above. More...
 
void shrink_to_fit ()
 Reduce the page table to fix the current size. More...
 
ValueTypeoperator[] (size_t i)
 Return a reference to the value at the specified offset. More...
 
const ValueTypeoperator[] (size_t i) const
 Return a const-reference to the value at the specified offset. More...
 
void fill (const ValueType &v)
 Set all elements in the page table to the specified value. More...
 
bool copy (ValueType *p, size_t count) const
 Copy the first count values in this PageArray into a raw c-style array, assuming it to be at least count elements long. More...
 
void copy (ValueType *p) const
 
void resize (size_t size)
 Resize this array to the specified size. More...
 
void resize (size_t size, const ValueType &v)
 Resize this array to the specified size and initialize all values to v. More...
 
size_t size () const
 Return the number of elements in this array. More...
 
size_t capacity () const
 Return the maximum number of elements that this array can contain without allocating more memory pages. More...
 
size_t freeCount () const
 Return the number of additional elements that can be added to this array without allocating more memory pages. More...
 
size_t pageCount () const
 Return the number of allocated memory pages. More...
 
size_t memUsage () const
 Return the memory footprint of this array in bytes. More...
 
bool isEmpty () const
 Return true if the container contains no elements. More...
 
bool isPartiallyFull () const
 Return true if the page table is partially full, i.e. the last non-empty page contains less than pageSize() elements. More...
 
void clear ()
 Removes all elements from the array and delete all pages. More...
 
Iterator begin ()
 Return a non-const iterator pointing to the first element. More...
 
Iterator end ()
 Return a non-const iterator pointing to the past-the-last element. More...
 
void sort ()
 Parallel sort of all the elements in ascending order. More...
 
void invSort ()
 Parallel sort of all the elements in descending order. More...
 
void merge (PagedArray &other)
 Transfer all the elements (and pages) from the other array to this array. More...
 
void print (std::ostream &os=std::cout) const
 Print information for debugging. More...
 
ConstIterator cbegin () const
 Return a const iterator pointing to the first element. More...
 
ConstIterator begin () const
 Return a const iterator pointing to the first element. More...
 
ConstIterator cend () const
 Return a const iterator pointing to the past-the-last element. More...
 
ConstIterator end () const
 Return a const iterator pointing to the past-the-last element. More...
 
template<typename Functor >
void sort (Functor func)
 Parallel sort of all the elements based on a custom functor with the api: More...
 

Static Public Member Functions

static size_t pageSize ()
 Return the number of elements per memory page. More...
 
static size_t log2PageSize ()
 Return log2 of the number of elements per memory page. More...
 

Friends

class ValueBuffer
 

Detailed Description

template<typename ValueT, size_t Log2PageSize = 10UL, template< typename... > class TableT = std::vector>
class openvdb::v5_2::util::PagedArray< ValueT, Log2PageSize, TableT >

Concurrent, page-based, dynamically-sized linear data structure with O(1) random access and STL-compliant iterators. It is primarily intended for applications that concurrently insert (a possibly unkown number of) elements into a dynamically growing linear array, and fast random access to said elements.

Note
Multiple threads can grow the page-table and push_back new elements concurrently. A ValueBuffer provides accelerated and threadsafe push_back at the cost of potentially re-ordering elements (when multiple instances are used).

This data structure employes contiguous pages of elements (like a std::deque) which avoids moving data when the capacity is out-grown and new pages are allocated. The size of the pages can be controlled with the Log2PageSize template parameter (defaults to 1024 elements of type ValueT). The TableT template parameter is used to define the data structure for the page table. The default, std::vector, offers fast random access in exchange for slower push_back, whereas std:deque offers faster push_back but slower random access.

There are three fundamentally different ways to insert elements to this container - each with different advanteges and disadvanteges.

The simplest way to insert elements is to use PagedArray::push_back e.g.

PagedArray<size_t> array;
for (size_t i=0; i<100000; ++i) array.push_back(i);

or with TBB task-based multi-threading

PagedArray<size_t> array;
tbb::parallel_for(
tbb::blocked_range<size_t>(0, 10000, array.pageSize()),
[&array](const tbb::blocked_range<size_t>& range) {
for (size_t i=range.begin(); i!=range.end(); ++i) array.push_back(i);
}
);

PagedArray::push_back has the advantage that it's thread-safe and preserves the ordering of the inserted elements. In fact it returns the linear offset to the added element which can then be used for fast O(1) random access. The disadvantage is it's the slowest of the three different ways of inserting elements.

The fastest way (by far) to insert elements by means of a PagedArray::ValueBuffer, e.g.

PagedArray<size_t> array;
for (size_t i=0; i<100000; ++i) buffer.push_back(i);
buffer.flush();

or

PagedArray<size_t> array;
{
//local scope of a single thread
for (size_t i=0; i<100000; ++i) buffer.push_back(i);
}

or with TBB task-based multi-threading

PagedArray<size_t> array;
tbb::parallel_for(
tbb::blocked_range<size_t>(0, 10000, array.pageSize()),
[&array](const tbb::blocked_range<size_t>& range) {
for (size_t i=range.begin(); i!=range.end(); ++i) buffer.push_back(i);
}
);

or with TBB thread-local storage for even better performance (due to fewer concurrent instantiations of partially full ValueBuffers)

PagedArray<size_t> array;
PagedArray<size_t>::ValueBuffer exemplar(array);//dummy used for initialization
tbb::enumerable_thread_specific<PagedArray<size_t>::ValueBuffer>
pool(exemplar);//thread local storage pool of ValueBuffers
tbb::parallel_for(
tbb::blocked_range<size_t>(0, 10000, array.pageSize()),
[&pool](const tbb::blocked_range<size_t>& range) {
PagedArray<size_t>::ValueBuffer &buffer = pool.local();
for (size_t i=range.begin(); i!=range.end(); ++i) buffer.push_back(i);
}
);
for (auto i=pool.begin(); i!=pool.end(); ++i) i->flush();

This technique generally outperforms PagedArray::push_back, std::vector::push_back, std::deque::push_back and even tbb::concurrent_vector::push_back. Additionally it is thread-safe as long as each thread has it's own instance of a PagedArray::ValueBuffer. The only disadvantage is the ordering of the elements is undefined if multiple instance of a PagedArray::ValueBuffer are employed. This is typically the case in the context of multi-threading, where the ordering of inserts are undefined anyway. Note that a local scope can be used to guarentee that the ValueBuffer has inserted all its elements by the time the scope ends. Alternatively the ValueBuffer can be explicitly flushed by calling ValueBuffer::flush.

The third way to insert elements is to resize the container and use random access, e.g.

PagedArray<int> array;
array.resize(100000);
for (int i=0; i<100000; ++i) array[i] = i;

or in terms of the random access iterator

PagedArray<int> array;
array.resize(100000);
for (auto i=array.begin(); i!=array.end(); ++i) *i = i.pos();

While this approach is both fast and thread-safe it suffers from the major disadvantage that the problem size, i.e. number of elements, needs to be known in advance. If that's the case you might as well consider using std::vector or a raw c-style array! In other words the PagedArray is most useful in the context of applications that involve multi-threading of dynamically growing linear arrays that require fast random access.

Member Typedef Documentation

using ValueType = ValueT

Constructor & Destructor Documentation

PagedArray ( )
default

Default constructor.

~PagedArray ( )
inline

Destructor removed all allocated pages.

PagedArray ( const PagedArray< ValueT, Log2PageSize, TableT > &  )
delete

Member Function Documentation

Iterator begin ( )
inline

Return a non-const iterator pointing to the first element.

ConstIterator begin ( ) const
inline

Return a const iterator pointing to the first element.

size_t capacity ( ) const
inline

Return the maximum number of elements that this array can contain without allocating more memory pages.

ConstIterator cbegin ( ) const
inline

Return a const iterator pointing to the first element.

ConstIterator cend ( ) const
inline

Return a const iterator pointing to the past-the-last element.

Warning
Iterator does not point to a valid element and should not be dereferenced!
void clear ( )
inline

Removes all elements from the array and delete all pages.

Warning
Not thread-safe!
bool copy ( ValueType p,
size_t  count 
) const
inline

Copy the first count values in this PageArray into a raw c-style array, assuming it to be at least count elements long.

Parameters
ppointer to an array that will used as the destination of the copy.
countnumber of elements to be copied.
void copy ( ValueType p) const
inline
Iterator end ( )
inline

Return a non-const iterator pointing to the past-the-last element.

Warning
Iterator does not point to a valid element and should not be dereferenced!
ConstIterator end ( ) const
inline

Return a const iterator pointing to the past-the-last element.

Warning
Iterator does not point to a valid element and should not be dereferenced!
void fill ( const ValueType v)
inline

Set all elements in the page table to the specified value.

Parameters
vvalue to be filled in all the existing pages of this PagedArray.
Note
Multi-threaded
size_t freeCount ( ) const
inline

Return the number of additional elements that can be added to this array without allocating more memory pages.

void invSort ( )
inline

Parallel sort of all the elements in descending order.

bool isEmpty ( ) const
inline

Return true if the container contains no elements.

bool isPartiallyFull ( ) const
inline

Return true if the page table is partially full, i.e. the last non-empty page contains less than pageSize() elements.

When the page table is partially full calling merge() or using a ValueBuffer will rearrange the ordering of existing elements.

static size_t log2PageSize ( )
inlinestatic

Return log2 of the number of elements per memory page.

size_t memUsage ( ) const
inline

Return the memory footprint of this array in bytes.

void merge ( PagedArray< ValueT, Log2PageSize, TableT > &  other)

Transfer all the elements (and pages) from the other array to this array.

Parameters
othernon-const reference to the PagedArray that will be merged into this PagedArray.
Note
The other PagedArray is empty on return.
Warning
The ordering of elements is undefined if this page table is partially full!
PagedArray& operator= ( const PagedArray< ValueT, Log2PageSize, TableT > &  )
delete
ValueType& operator[] ( size_t  i)
inline

Return a reference to the value at the specified offset.

Parameters
ilinear offset of the value to be accessed.
Note
This random access has constant time complexity.
Warning
It is assumed that the i'th element is already allocated!
const ValueType& operator[] ( size_t  i) const
inline

Return a const-reference to the value at the specified offset.

Parameters
ilinear offset of the value to be accessed.
Note
This random access has constant time complexity.
Warning
It is assumed that the i'th element is already allocated!
size_t pageCount ( ) const
inline

Return the number of allocated memory pages.

static size_t pageSize ( )
inlinestatic

Return the number of elements per memory page.

void print ( std::ostream &  os = std::cout) const
inline

Print information for debugging.

size_t push_back ( const ValueType value)
inline

Thread safe insertion, adds a new element at the end and increases the container size by one and returns the linear offset for the inserted element.

Parameters
valuevalue to be added to this PagedArray

Constant time complexity. May allocate a new page.

size_t push_back_unsafe ( const ValueType value)
inline

Slightly faster than the thread-safe push_back above.

Parameters
valuevalue to be added to this PagedArray
Note
For best performance consider using the ValueBuffer!
Warning
Not thread-safe!
void resize ( size_t  size)
inline

Resize this array to the specified size.

Parameters
sizenumber of elements that this PageArray will contain.

Will grow or shrink the page table to contain the specified number of elements. It will affect the size(), iteration will go over all those elements, push_back will insert after them and operator[] can be used directly access them.

Note
No reserve method is implemented due to efficiency concerns (especially for the ValueBuffer) from having to deal with empty pages.
Warning
Not thread-safe!
void resize ( size_t  size,
const ValueType v 
)
inline

Resize this array to the specified size and initialize all values to v.

Parameters
sizenumber of elements that this PageArray will contain.
vvalue of all the size values.

Will grow or shrink the page table to contain the specified number of elements. It will affect the size(), iteration will go over all those elements, push_back will insert after them and operator[] can be used directly access them.

Note
No reserve method is implemented due to efficiency concerns (especially for the ValueBuffer) from having to deal with empty pages.
Warning
Not thread-safe!
void shrink_to_fit ( )

Reduce the page table to fix the current size.

Warning
Not thread-safe!
size_t size ( ) const
inline

Return the number of elements in this array.

void sort ( )
inline

Parallel sort of all the elements in ascending order.

void sort ( Functor  func)
inline

Parallel sort of all the elements based on a custom functor with the api:

bool operator()(const ValueT& a, const ValueT& b)

which returns true if a comes before b.

Friends And Related Function Documentation

friend class ValueBuffer
friend

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