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TableLocker.h
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1//# TableLocker.h: Class to hold a (user) lock on a table
2//# Copyright (C) 1998,2000
3//# Associated Universities, Inc. Washington DC, USA.
4//#
5//# This library is free software; you can redistribute it and/or modify it
6//# under the terms of the GNU Library General Public License as published by
7//# the Free Software Foundation; either version 2 of the License, or (at your
8//# option) any later version.
9//#
10//# This library is distributed in the hope that it will be useful, but WITHOUT
11//# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12//# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
13//# License for more details.
14//#
15//# You should have received a copy of the GNU Library General Public License
16//# along with this library; if not, write to the Free Software Foundation,
17//# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
18//#
19//# Correspondence concerning AIPS++ should be addressed as follows:
20//# Internet email: aips2-request@nrao.edu.
21//# Postal address: AIPS++ Project Office
22//# National Radio Astronomy Observatory
23//# 520 Edgemont Road
24//# Charlottesville, VA 22903-2475 USA
25//#
26//# $Id$
27
28#ifndef TABLES_TABLELOCKER_H
29#define TABLES_TABLELOCKER_H
30
31
32//# Includes
33#include <casacore/casa/aips.h>
34#include <casacore/tables/Tables/Table.h>
35#include <casacore/tables/Tables/TableLock.h>
36
37
38namespace casacore { //# NAMESPACE CASACORE - BEGIN
39
40// <summary>
41// Class to hold a (user) lock on a table.
42// </summary>
43
44// <use visibility=export>
45
46// <reviewed reviewer="UNKNOWN" date="before2004/08/25" tests="tTableLockSync.cc">
47// </reviewed>
48
49// <prerequisite>
50//# Classes you should understand before using this one.
51// <li> <linkto class=Table>Table</linkto>
52// <li> <linkto class=TableLock>TableLock</linkto>
53// </prerequisite>
54
55// <synopsis>
56// Class TableLocker can be used to acquire a (user) lock on a table.
57// The lock can be a read or write lock.
58// The destructor only releases the lock if the lock was acquired by the
59// constructor.
60// <p>
61// TableLocker simply uses the <src>lock</src> and <src>unlock</src>
62// function of class Table.
63// The advantage of TableLocker over these functions is that the
64// destructor of TableLocker is called automatically by the system,
65// so unlocking the table does not need to be done explicitly and
66// cannot be forgotten. Especially in case of exception handling this
67// can be quite an adavantage.
68// <p>
69// This class is meant to be used with the UserLocking option.
70// It can, however, also be used with the other locking options.
71// In case of PermanentLocking(Wait) it won't do anything at all.
72// In case of AutoLocking it will acquire and release the lock when
73// needed. However, it is possible that the system releases an
74// auto lock before the TableLocker destructor is called.
75// </synopsis>
76
77// <example>
78// <srcblock>
79// // Open a table to be updated.
80// Table myTable ("theTable", TableLock::UserLocking, Table::Update);
81// // Start of some critical section requiring a lock.
82// {
83// TableLocker lock1 (myTable);
84// ... write the data
85// }
86// // The TableLocker destructor invoked by } unlocked the table.
87// </srcblock>
88// </example>
89
90// <motivation>
91// TableLocker makes it easier to unlock a table.
92// </motivation>
93
94//# <todo asof="$DATE:$">
95//# A List of bugs, limitations, extensions or planned refinements.
96//# </todo>
97
98
100{
101public:
102 // The constructor acquires a read or write lock on a table
103 // which is released by the destructor.
104 // If the table was already locked, the destructor will
105 // not unlock the table.
106 // <br>
107 // The number of attempts (default = forever) can be specified when
108 // acquiring the lock does not succeed immediately. When nattempts>1,
109 // the system waits 1 second between each attempt, so nattempts
110 // is more or less equal to a wait period in seconds.
111 // An exception is thrown when the lock cannot be acquired.
112 explicit TableLocker (Table& table,
114 uInt nattempts = 0);
115
116 // If locked, the destructor releases the lock and flushes the data.
118
119 // Has this process the read or write lock, thus can the table
120 // be read or written safely?
122
123private:
124 // The copy constructor and assignment are not possible.
125 // Note that only one lock can be held on a table, so copying a
126 // TableLocker object imposes great difficulties which objects should
127 // release the lock.
128 // It can be solved by turning TableLocker into a handle class
129 // with a reference counted body class.
130 // However, that will only be done when the need arises.
131 // <group>
134 // </group>
135
136 //# Variables.
139};
140
141
143{
144 return itsTable.hasLock (type);
145}
146
147
148
149} //# NAMESPACE CASACORE - END
150
151#endif
LockType
Define the possible lock types.
Definition FileLocker.h:95
@ Write
Acquire a write lock.
Definition FileLocker.h:99
TableLocker(const TableLocker &)
The copy constructor and assignment are not possible.
~TableLocker()
If locked, the destructor releases the lock and flushes the data.
TableLocker & operator=(const TableLocker &)
TableLocker(Table &table, FileLocker::LockType=FileLocker::Write, uInt nattempts=0)
The constructor acquires a read or write lock on a table which is released by the destructor.
Bool hasLock(FileLocker::LockType=FileLocker::Write) const
Has this process the read or write lock, thus can the table be read or written safely?
Bool hasLock(FileLocker::LockType=FileLocker::Write) const
Has this process the read or write lock, thus can the table be read or written safely?
Definition Table.h:1121
this file contains all the compiler specific defines
Definition mainpage.dox:28
unsigned int uInt
Definition aipstype.h:51
bool Bool
Define the standard types used by Casacore.
Definition aipstype.h:42