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casacore::TableLock Class Reference

Class to hold table lock options. More...

#include <TableLock.h>

Inheritance diagram for casacore::TableLock:
casacore::TableLockData

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...
 
TableLockoperator= (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 was 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

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.

Motivation

Encapsulate Table locking info.

Definition at line 65 of file TableLock.h.

Member Enumeration Documentation

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.

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 75 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 194 of file TableLock.h.

References itsInterval.

Bool casacore::TableLock::isPermanent ( ) const
inline

Is permanent locking used?

Definition at line 188 of file TableLock.h.

References itsOption, PermanentLocking, and PermanentLockingWait.

static Bool casacore::TableLock::lockingDisabled ( )
static

Is table locking disabled (because AIPS_TABLE_NOLOCKING was set)?

uInt casacore::TableLock::maxWait ( ) const
inline

Get the maximum wait period in AutoLocking mode.

Definition at line 199 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 178 of file TableLock.h.

References itsOption.

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

Bool casacore::TableLock::readLocking ( ) const
inline

Is read locking needed?

Definition at line 183 of file TableLock.h.

References itsReadLocking.

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

Member Data Documentation

double casacore::TableLock::itsInterval
private

Definition at line 167 of file TableLock.h.

Referenced by interval().

Bool casacore::TableLock::itsIsDefaultInterval
private

Definition at line 169 of file TableLock.h.

Bool casacore::TableLock::itsIsDefaultLocking
private

Definition at line 168 of file TableLock.h.

uInt casacore::TableLock::itsMaxWait
private

Definition at line 166 of file TableLock.h.

Referenced by maxWait().

LockOption casacore::TableLock::itsOption
private

Definition at line 164 of file TableLock.h.

Referenced by isPermanent(), and option().

Bool casacore::TableLock::itsReadLocking
private

Definition at line 165 of file TableLock.h.

Referenced by readLocking().


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