mcs_rwlock Class Reference

Shore read-write lock:: many-reader/one-writer spin lock. More...

#include <latches.h>

Inheritance diagram for mcs_rwlock:

Public Types
enum	rwmode_t { NONE = 0, WRITER = 0x1, READER = 0x2 }

Public Member Functions
	mcs_rwlock ()
	~mcs_rwlock ()
rwmode_t	mode () const
	Return the mode in which this lock is held by anyone. More...
bool	is_locked () const
	True if locked in any mode. More...
int	num_holders () const
	1 if held in write mode, else it's the number of readers More...
bool	has_reader () const
	True iff has one or more readers. More...
bool	has_writer () const
	True iff has a writer (never more than 1) More...
bool	attempt_read ()
	True if success. More...
void	acquire_read ()
	Wait (spin) until acquired. More...
void	release_read ()
	This thread had better hold the lock in read mode. More...
bool	attempt_write ()
	True if success. More...
void	acquire_write ()
	Wait (spin) until acquired. More...
void	release_write ()
	This thread had better hold the lock in write mode. More...
bool	attempt_upgrade ()
	Try to upgrade from READ to WRITE mode. Fail if any other threads are waiting. More...
void	downgrade ()
	Atomically downgrade the lock from WRITE to READ mode. More...

Private Types
typedef queue_based_lock_t	parent_lock

Private Member Functions
int	_spin_on_writer ()
void	_spin_on_readers ()
bool	_attempt_write (unsigned int expected)
void	_add_when_writer_leaves (int delta)

Private Attributes
unsigned int volatile	_holders

Additional Inherited Members
Protected Member Functions inherited from mcs_lock
	mcs_lock ()
void	spin_on_waiting (qnode *me)
bool	attempt (ext_qnode *me)
bool	attempt (qnode *me)
void *	acquire (ext_qnode *me)
void *	acquire (qnode *me)
qnode *	__unsafe_begin_acquire (qnode *me)
void *	__unsafe_end_acquire (qnode *me, qnode *pred)
qnode *	spin_on_next (qnode *me)
void	release (ext_qnode *me)
void	release (ext_qnode &me)
void	release (qnode &me)
void	release (qnode *me)
bool	is_mine (ext_qnode *me)
Protected Attributes inherited from mcs_lock
qnode *	_tail

Detailed Description

Shore read-write lock:: many-reader/one-writer spin lock.

This read-write lock is implemented around a queue-based lock. It is the basis for latches in the storage manager.

Use this to protect data structures that get constantly hammered by short reads, and less frequently (but still often) by short writes.

"Short" is the key word here, since this is spin-based.

Member Typedef Documentation

parent_lock

typedef queue_based_lock_t mcs_rwlock::parent_lock

private

Member Enumeration Documentation

rwmode_t

enum mcs_rwlock::rwmode_t

Enumerator
NONE
WRITER
READER

Constructor & Destructor Documentation

mcs_rwlock()

mcs_rwlock::mcs_rwlock ( )

inline

~mcs_rwlock()

mcs_rwlock::~mcs_rwlock ( )

inline

Member Function Documentation

_add_when_writer_leaves()

void mcs_rwlock::_add_when_writer_leaves ( int  delta )

private

_attempt_write()

bool mcs_rwlock::_attempt_write ( unsigned int  expected )

private

_spin_on_readers()

void mcs_rwlock::_spin_on_readers ( )

private

_spin_on_writer()

int mcs_rwlock::_spin_on_writer ( )

private

acquire_read()

void mcs_rwlock::acquire_read

(

)

Wait (spin) until acquired.

acquire_write()

void mcs_rwlock::acquire_write

(

)

Wait (spin) until acquired.

attempt_read()

bool mcs_rwlock::attempt_read

(

)

True if success.

attempt_upgrade()

bool mcs_rwlock::attempt_upgrade

(

)

Try to upgrade from READ to WRITE mode. Fail if any other threads are waiting.

attempt_write()

bool mcs_rwlock::attempt_write

(

)

True if success.

downgrade()

void mcs_rwlock::downgrade

(

)

Atomically downgrade the lock from WRITE to READ mode.

has_reader()

bool mcs_rwlock::has_reader ( ) const

inline

True iff has one or more readers.

has_writer()

bool mcs_rwlock::has_writer ( ) const

inline

True iff has a writer (never more than 1)

is_locked()

bool mcs_rwlock::is_locked ( ) const

inline

True if locked in any mode.

mode()

rwmode_t mcs_rwlock::mode ( ) const

inline

Return the mode in which this lock is held by anyone.

num_holders()

int mcs_rwlock::num_holders ( ) const

inline

1 if held in write mode, else it's the number of readers

release_read()

void mcs_rwlock::release_read

(

)

This thread had better hold the lock in read mode.

release_write()

void mcs_rwlock::release_write

(

)

This thread had better hold the lock in write mode.

Member Data Documentation

_holders

unsigned int volatile mcs_rwlock::_holders

private

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

• src/sm/latches.h
• src/sm/latches.cpp