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LatticeLocker.h
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//# LatticeLocker.h: Class to hold a (user) lock on a lattice
//# Copyright (C) 1999,2000
//# Associated Universities, Inc. Washington DC, USA.
//#
//# This library is free software; you can redistribute it and/or modify it
//# under the terms of the GNU Library General Public License as published by
//# the Free Software Foundation; either version 2 of the License, or (at your
//# option) any later version.
//#
//# This library is distributed in the hope that it will be useful, but WITHOUT
//# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
//# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
//# License for more details.
//#
//# You should have received a copy of the GNU Library General Public License
//# along with this library; if not, write to the Free Software Foundation,
//# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
//#
//# Correspondence concerning AIPS++ should be addressed as follows:
//# Internet email: casa-feedback@nrao.edu.
//# Postal address: AIPS++ Project Office
//# National Radio Astronomy Observatory
//# 520 Edgemont Road
//# Charlottesville, VA 22903-2475 USA
#ifndef LATTICES_LATTICELOCKER_H
#define LATTICES_LATTICELOCKER_H
//# Includes
#include <casacore/casa/aips.h>
#include <casacore/lattices/Lattices/LatticeBase.h>
#include <casacore/tables/Tables/TableLock.h>
namespace casacore { //# NAMESPACE CASACORE - BEGIN
// <summary>
// Class to hold a (user) lock on a lattice.
// </summary>
// <use visibility=export>
// <reviewed reviewer="" date="" tests="tTableLockSync.cc">
// </reviewed>
// <prerequisite>
//# Classes you should understand before using this one.
// <li> <linkto class=Lattice>Lattice</linkto>
// <li> <linkto class=TableLock>TableLock</linkto>
// </prerequisite>
// <synopsis>
// Class LatticeLocker can be used to acquire a (user) lock on a lattice.
// The lock can be a read or write lock.
// The destructor releases the lock when needed.
// <p>
// LatticeLocker simply uses the <src>lock</src> and <src>unlock</src>
// function of class Lattice.
// The advantage of LatticeLocker over these functions is that the
// destructor of LatticeLocker is called automatically by the system,
// so unlocking the lattice does not need to be done explicitly and
// cannot be forgotten. Especially in case of exception handling this
// can be quite an adavantage.
// <p>
// This class is meant to be used with the UserLocking option.
// It can, however, also be used with the other locking options.
// In case of PermanentLocking(Wait) it won't do anything at all.
// In case of AutoLocking it will acquire and release the lock when
// needed. However, it is possible that the system releases an
// auto lock before the LatticeLocker destructor is called.
// <p>
// The constructor of LatticeLocker will look if the lattice is
// already appropriately locked. If so, it will set a flag to
// prevent the destructor from unlocking the lattice. In this way
// nested locks can be used. I.e. one can safely use LatticeLocker
// in a function without having to be afraid that its destructor
// would undo a lock set in a higher function.
// <br>Similarly LatticeLocker will remember if a lattice was
// already read-locked, when a write-lock is acquired. In such a
// case the destructor will try to ensure that the lattice remains
// read-locked.
// </synopsis>
// <example>
// <srcblock>
// // Open a lattice to be updated.
// PagedArray<Float> myLattice (Table ("theLattice",
// LatticeLock::UserLocking,
// Lattice::Update);
// // Start of some critical section requiring a lock.
// {
// LatticeLocker lock1 (myLattice, FileLocker::Write);
// ... write the data
// }
// // The LatticeLocker destructor invoked by } unlocks the table.
// </srcblock>
// </example>
// <motivation>
// LatticeLocker makes it easier to unlock a lattice.
// It also makes it easier to use locking in a nested way.
// </motivation>
//# <todo asof="$DATE:$">
//# A List of bugs, limitations, extensions or planned refinements.
//# </todo>
class LatticeLocker
{
public:
// The constructor acquires a read or write lock on a lattice.
// If the lattice was already locked, the destructor will
// not unlock the lattice. This means that the class can be used in
// a nested way.
// <br>
// The number of attempts (default = forever) can be specified when
// acquiring the lock does not succeed immediately. When nattempts>1,
// the system waits 1 second between each attempt, so nattempts
// is more or less equal to a wait period in seconds.
// An exception is thrown when the lock cannot be acquired.
explicit LatticeLocker (LatticeBase& lattice,
FileLocker::LockType,
uInt nattempts = 0);
// If the constructor acquired the lock, the destructor releases
// the lock and flushes the data if changed.
~LatticeLocker();
// Has this process the read or write lock, thus can the table
// be read or written safely?
Bool hasLock (FileLocker::LockType) const;
private:
// The copy constructor and assignment are not possible.
// Note that only one lock can be held on a lattice, so copying a
// TableLocker object imposes great difficulties which object should
// release the lock.
// It can be solved by turning LatticeLocker into a handle class
// with a reference counted body class.
// However, that will only be done when the need arises.
// <group>
LatticeLocker (const LatticeLocker&);
LatticeLocker& operator= (const LatticeLocker&);
// </group>
//# Variables.
LatticeBase* itsLatticePtr;
Bool itsOwnLock;
Bool itsHadReadLock;
};
inline Bool LatticeLocker::hasLock (FileLocker::LockType type) const
{
return itsLatticePtr->hasLock (type);
}
} //# NAMESPACE CASACORE - END
#endif
casacore::type
casacore::FileLocker::LockType
LockType
Define the possible lock types.
Definition FileLocker.h:93
casacore::LatticeBase
Definition LatticeBase.h:79
casacore::LatticeLocker::~LatticeLocker
~LatticeLocker()
If the constructor acquired the lock, the destructor releases the lock and flushes the data if change...
casacore::LatticeLocker::LatticeLocker
LatticeLocker(LatticeBase &lattice, FileLocker::LockType, uInt nattempts=0)
The constructor acquires a read or write lock on a lattice.
casacore::LatticeLocker::operator=
LatticeLocker & operator=(const LatticeLocker &)
casacore::LatticeLocker::itsOwnLock
Bool itsOwnLock
Definition LatticeLocker.h:150
casacore::LatticeLocker::LatticeLocker
LatticeLocker(const LatticeLocker &)
The copy constructor and assignment are not possible.
casacore::LatticeLocker::itsLatticePtr
LatticeBase * itsLatticePtr
Definition LatticeLocker.h:149
casacore::LatticeLocker::itsHadReadLock
Bool itsHadReadLock
Definition LatticeLocker.h:151
casacore::LatticeLocker::hasLock
Bool hasLock(FileLocker::LockType) const
Has this process the read or write lock, thus can the table be read or written safely?
Definition LatticeLocker.h:155
casacore
this file contains all the compiler specific defines
Definition mainpage.dox:28
casacore::uInt
unsigned int uInt
Definition aipstype.h:49
casacore::Bool
bool Bool
Define the standard types used by Casacore.
Definition aipstype.h:40