ARWLock Class Reference

#include <arwlock.h>

Detailed Description

The ARWLock class implements an asymmetric read write lock. It's a mutex that allows access of multiple readers or one exclusive writer. The readers are preferred and the writes are slower. The read to write ratio should at least be 10 : 1, with more writes its only marginally faster or even slower than a RWSpinlock.

In contrast to RWSpinlock this scales when multiple readers are locking and performance does not degrade. This comes at the cost of a slightly higher overhead and more memory (about 128 to 256 bytes are used for the ARWLock, depending on the number of threads).

THREADSAFE.

Public Member Functions

 ARWLock ()
 
 ~ARWLock ()
 
void ReadLock ()
 
void ReadUnlock ()
 
void WriteLock ()
 
void WriteUnlock ()
 
MAXON_WARN_UNUSED Bool AttemptWriteLock ()
 

Private Member Functions

 MAXON_DISALLOW_COPY_AND_ASSIGN (ARWLock)
 

Private Attributes

ARWArray * _reader
 
Int16 _readerIndex
 
Int16 _readerOffset
 
UChar _readerSetMask
 
UChar _readerClearMask
 
Spinlock_writer
 

Constructor & Destructor Documentation

◆ ARWLock()

ARWLock ( )

◆ ~ARWLock()

~ARWLock ( )

Member Function Documentation

◆ MAXON_DISALLOW_COPY_AND_ASSIGN()

MAXON_DISALLOW_COPY_AND_ASSIGN ( ARWLock  )
private

◆ ReadLock()

void ReadLock ( )

Read locks a user level spin lock. Does not trash other thread's cache lines or force synchronization. If a write is pending an exponential backoff pause loop is used to wait. Creates a memory barrier. THREADSAFE.

◆ ReadUnlock()

void ReadUnlock ( )

Balances a preceding ReadLock() when the reading thread has finished. Creates a memory barrier. THREADSAFE.

◆ WriteLock()

void WriteLock ( )

Write locks a user level spin lock. As long as there are pending readers an exponential backoff pause loop is used to wait. Creates a memory barrier. THREADSAFE.

◆ WriteUnlock()

void WriteUnlock ( )

Balances a preceding WriteLock() when the writing thread has finished. Creates a memory barrier. THREADSAFE.

◆ AttemptWriteLock()

MAXON_WARN_UNUSED Bool AttemptWriteLock ( )

Tries to write lock. Creates a memory barrier if the lock can be taken. Immediately returns with false if there are pending reads or writes.

Returns
True if successful. THREADSAFE.

Member Data Documentation

◆ _reader

ARWArray* _reader
private

◆ _readerIndex

Int16 _readerIndex
private

◆ _readerOffset

Int16 _readerOffset
private

◆ _readerSetMask

UChar _readerSetMask
private

◆ _readerClearMask

UChar _readerClearMask
private

◆ _writer

Spinlock* _writer
private