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/*=========================================================================
Program: Visualization Toolkit
Module: vtkSMPThreadLocalImpl.h
Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
All rights reserved.
See Copyright.txt or http://www.kitware.com/Copyright.htm for details.
This software is distributed WITHOUT ANY WARRANTY; without even
the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE. See the above copyright notice for more information.
=========================================================================*/
// Thread Specific Storage is implemented as a Hash Table, with the Thread Id
// as the key and a Pointer to the data as the value. The Hash Table implements
// Open Addressing with Linear Probing. A fixed-size array (HashTableArray) is
// used as the hash table. The size of this array is allocated to be large
// enough to store thread specific data for all the threads with a Load Factor
// of 0.5. In case the number of threads changes dynamically and the current
// array is not able to accommodate more entries, a new array is allocated that
// is twice the size of the current array. To avoid rehashing and blocking the
// threads, a rehash is not performed immediately. Instead, a linked list of
// hash table arrays is maintained with the current array at the root and older
// arrays along the list. All lookups are sequentially performed along the
// linked list. If the root array does not have an entry, it is created for
// faster lookup next time. The ThreadSpecific::GetStorage() function is thread
// safe and only blocks when a new array needs to be allocated, which should be
// rare.
#ifndef vtkSMPThreadLocalImpl_h
#define vtkSMPThreadLocalImpl_h
#include "vtkCommonCoreModule.h" // For export macro
#include "vtkAtomic.h"
#include "vtkConfigure.h"
#include "vtkSystemIncludes.h"
#include <omp.h>
namespace detail
{
typedef void* ThreadIdType;
typedef vtkTypeUInt32 HashType;
typedef void* StoragePointerType;
struct Slot
{
vtkAtomic<ThreadIdType> ThreadId;
omp_lock_t ModifyLock;
StoragePointerType Storage;
Slot();
~Slot();
private:
// not copyable
Slot(const Slot&);
void operator=(const Slot&);
};
struct HashTableArray
{
size_t Size, SizeLg;
vtkAtomic<size_t> NumberOfEntries;
Slot *Slots;
HashTableArray *Prev;
explicit HashTableArray(size_t sizeLg);
~HashTableArray();
private:
// disallow copying
HashTableArray(const HashTableArray&);
void operator=(const HashTableArray&);
};
class VTKCOMMONCORE_EXPORT ThreadSpecific
{
public:
explicit ThreadSpecific(unsigned numThreads);
~ThreadSpecific();
StoragePointerType& GetStorage();
size_t Size() const;
private:
vtkAtomic<HashTableArray*> Root;
vtkAtomic<size_t> Count;
friend class ThreadSpecificStorageIterator;
};
inline size_t ThreadSpecific::Size() const
{
return this->Count;
}
class ThreadSpecificStorageIterator
{
public:
ThreadSpecificStorageIterator()
: ThreadSpecificStorage(NULL), CurrentArray(NULL), CurrentSlot(0)
{
}
void SetThreadSpecificStorage(ThreadSpecific &threadSpecifc)
{
this->ThreadSpecificStorage = &threadSpecifc;
}
void SetToBegin()
{
this->CurrentArray = this->ThreadSpecificStorage->Root;
this->CurrentSlot = 0;
if (!this->CurrentArray->Slots->Storage)
{
this->Forward();
}
}
void SetToEnd()
{
this->CurrentArray = NULL;
this->CurrentSlot = 0;
}
bool GetInitialized() const
{
return this->ThreadSpecificStorage != NULL;
}
bool GetAtEnd() const
{
return this->CurrentArray == NULL;
}
void Forward()
{
for (;;)
{
if (++this->CurrentSlot >= this->CurrentArray->Size)
{
this->CurrentArray = this->CurrentArray->Prev;
this->CurrentSlot = 0;
if (!this->CurrentArray)
{
break;
}
}
Slot *slot = this->CurrentArray->Slots + this->CurrentSlot;
if (slot->Storage)
{
break;
}
}
}
StoragePointerType& GetStorage() const
{
Slot *slot = this->CurrentArray->Slots + this->CurrentSlot;
return slot->Storage;
}
bool operator==(const ThreadSpecificStorageIterator &it) const
{
return (this->ThreadSpecificStorage == it.ThreadSpecificStorage) &&
(this->CurrentArray == it.CurrentArray) &&
(this->CurrentSlot == it.CurrentSlot);
}
private:
ThreadSpecific *ThreadSpecificStorage;
HashTableArray *CurrentArray;
size_t CurrentSlot;
};
} // detail;
#endif
// VTK-HeaderTest-Exclude: vtkSMPThreadLocalImpl.h
|
