casacore::TableLock Class Reference

Class to hold table lock options. More...

#include <TableLock.h>

Inheritance diagram for casacore::TableLock:

Public Types
enum	LockOption {   PermanentLocking,   PermanentLockingWait,   AutoLocking,   UserLocking,   AutoNoReadLocking,   UserNoReadLocking,   NoLocking,   DefaultLocking }
	Define the possible table locking options. More...

Public Member Functions
	TableLock (LockOption option=DefaultLocking)
	Construct with given option and interval. More...
	TableLock (LockOption option, double inspectionInterval, uInt maxWait=0)
	TableLock (const TableLock &that)
	Copy constructor. More...
TableLock &	operator= (const TableLock &that)
	Assignment. More...
void	merge (const TableLock &that)
	Merge that TableLock with this TableLock object by taking the maximum option and minimum inspection interval. More...
LockOption	option () const
	Get the locking option. More...
Bool	readLocking () const
	Is read locking needed? More...
Bool	isPermanent () const
	Is permanent locking used? More...
double	interval () const
	Get the inspection interval. More...
uInt	maxWait () const
	Get the maximum wait period in AutoLocking mode. More...

Static Public Member Functions
static Bool	lockingDisabled ()
	Is table locking disabled (because AIPS_TABLE_NOLOCKING or table.nolocking is set)? More...

Private Member Functions
void	init ()
	Set itsOption and itsReadLocking when needed. More...

Private Attributes
LockOption	itsOption
Bool	itsReadLocking
uInt	itsMaxWait
double	itsInterval
Bool	itsIsDefaultLocking
Bool	itsIsDefaultInterval

Detailed Description

Class to hold table lock options.

Intended use:

Internal

Review Status

Reviewed By:

UNKNOWN

Date Reviewed:

before2004/08/25

Test programs:

tTable

Prerequisite

• class Table
• class LockFile

Synopsis

This class keeps the Table lock options. Currently these are the LockingOption and the inspection interval.

It also keeps the LockFile object used to do the actual locking/unlocking.

It is possible to disable locking by building casacore with -DAIPS_TABLE_NOLOCKING or by setting the aipsrc variable table.nolocking=true.

Motivation

Encapsulate Table locking info.

Definition at line 68 of file TableLock.h.

Member Enumeration Documentation

enum casacore::TableLock::LockOption

Define the possible table locking options.

They offer the user the possibility to lock and synchronize access to the table. A lot of locking degrades table performance; not only because acquiring/releasing locks takes time, but especially because table data has to be synchronized (thus written to disk) when a lock is released. Otherwise the other processes see data which is not up-to-date.

Building Casacore with -DTABLE_NOLOCKING or setting aipsrc variable table.nolocking=1 forces lock option NoLocking.

Enumerator
PermanentLocking	The table is permanently locked. A lock is set at the beginning and only released when the table is closed. A read lock is used when the table is opened for readonly; otherwise a write lock is used. This means that multiple readers are possible. The Table constructor exits with an exception when the lock cannot be acquired.
PermanentLockingWait	The same as above, but the table constructor waits until the lock gets available.
AutoLocking	The system takes care of acquiring/releasing locks. In principle it keeps the table locked, but from time to time (defined by the inspection interval) it is checked whether another process wants to access the table. If so, the lock is released and probably re-acquired later. This mode is the default mode.
UserLocking	The user is taking care of locking the table by means of the Table functions lock and unlock. In this way transaction processing can be implemented.
AutoNoReadLocking	The system takes care of acquiring/releasing locks. It is similar to AutoLocking, but no locks are needed for reading.
UserNoReadLocking	The user is taking care of locking the table by means of the Table functions lock and unlock. It is similar to UserLocking, but no locks are needed for reading.
NoLocking	Do not do any locking at all. This should be used with care because concurrent access might result in table corruption.
DefaultLocking	This is the default locking option. It means that AutoLocking will be used if the table is not opened yet. Otherwise the locking options of the PlainTable object already in use will be used.

Definition at line 81 of file TableLock.h.

Constructor & Destructor Documentation

casacore::TableLock::TableLock

(

LockOption

option = DefaultLocking

)

Construct with given option and interval.

The default LockOption is AutoLocking. In case of AutloLocking the inspection interval defines how often the table system checks if another process needs a lock on the table. It defaults to 5 seconds. The maxWait defines the maximum number of seconds the table system waits when acquiring a lock in AutoLocking mode. The default is 0 seconds meaning indefinitely.

casacore::TableLock::TableLock	(	LockOption	option,
		double	inspectionInterval,
		uInt	maxWait = 0
	)

casacore::TableLock::TableLock

(

const TableLock &

that

)

Copy constructor.

Member Function Documentation

void casacore::TableLock::init ( )

private

Set itsOption and itsReadLocking when needed.

double casacore::TableLock::interval ( ) const

inline

Get the inspection interval.

Definition at line 200 of file TableLock.h.

References itsInterval.

Bool casacore::TableLock::isPermanent ( ) const

inline

Is permanent locking used?

Definition at line 194 of file TableLock.h.

References itsOption, PermanentLocking, and PermanentLockingWait.

static Bool casacore::TableLock::lockingDisabled ( )

static

Is table locking disabled (because AIPS_TABLE_NOLOCKING or table.nolocking is set)?

uInt casacore::TableLock::maxWait ( ) const

inline

Get the maximum wait period in AutoLocking mode.

Definition at line 205 of file TableLock.h.

References itsMaxWait.

void casacore::TableLock::merge

(

const TableLock &

that

)

Merge that TableLock with this TableLock object by taking the maximum option and minimum inspection interval.

The option order (ascending) is UserLocking, AutoLocking, PermanentLocking. When an interval was defaulted, it is not taken into account. An option DefaultLocking is not taken into account.

TableLock& casacore::TableLock::operator=

(

const TableLock &

that

)

Assignment.

TableLock::LockOption casacore::TableLock::option ( ) const

inline

Get the locking option.

Definition at line 184 of file TableLock.h.

References itsOption.

Referenced by casacore::TableLockData::autoRelease().

Bool casacore::TableLock::readLocking ( ) const

inline

Is read locking needed?

Definition at line 189 of file TableLock.h.

References itsReadLocking.

Referenced by casacore::ColumnSet::checkReadLock().

Member Data Documentation

double casacore::TableLock::itsInterval

private

Definition at line 173 of file TableLock.h.

Referenced by interval().

Bool casacore::TableLock::itsIsDefaultInterval

private

Definition at line 175 of file TableLock.h.

Bool casacore::TableLock::itsIsDefaultLocking

private

Definition at line 174 of file TableLock.h.

uInt casacore::TableLock::itsMaxWait

private

Definition at line 172 of file TableLock.h.

Referenced by maxWait().

LockOption casacore::TableLock::itsOption

private

Definition at line 170 of file TableLock.h.

Referenced by isPermanent(), and option().

Bool casacore::TableLock::itsReadLocking

private

Definition at line 171 of file TableLock.h.

Referenced by readLocking().

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

• tables/Tables/TableLock.h