casacore
FileLocker.h
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1//# FileLocker.h: Class to handle file locking
2//# Copyright (C) 1997,1998,1999,2000
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 CASA_FILELOCKER_H
29#define CASA_FILELOCKER_H
30
31
32//# Includes
33#include <casacore/casa/aips.h>
34
35namespace casacore { //# NAMESPACE CASACORE - BEGIN
36
37//# Forward Declarations
38class String;
39
40
41// <summary>
42// Class to handle file locking.
43// </summary>
44
45// <use visibility=export>
46
47// <reviewed reviewer="UNKNOWN" date="before2004/08/25" tests="tLockFile" demos="">
48// </reviewed>
49
50// <prerequisite>
51// <li> man page of fcntl
52// </prerequisite>
53
54// <synopsis>
55// This class handles file locking by means of the fcntl SETLK function.
56// Locking of files on NFS-mounted file systems works correctly
57// as long as the NFS lockd and statd deamons are configured correctly.
58// Otherwise lock requests may be granted incorrectly.
59// <p>
60// Acquiring a lock can be done for a read or a write lock.
61// Multiple locks on a file can exist as long as they are all
62// read locks. When a write lock is involved, no other lock can exist.
63// It is possible to acquire a lock in 2 ways:
64// <ul>
65// <li>Wait until the lock request is granted; i.e. until the processes
66// holding a lock on the file release their lock.
67// <li>Do several attempts; between each attempt it sleeps 1 second.
68// Note that nattempts=1 means it returns immediately when the
69// lock request could not be granted.
70// </ul>
71// </synopsis>
72
73// <example>
74// <srcblock>
75// int fd = open ("file.name");
76// FileLocker lock(fd);
77// if (lock.acquire()) {
78// ... do something with the file ...
79// lock.release();
80// }else{
81// cout << lock.lastMessage() << endl;
82// }
83// </srcblock>
84// </example>
85
86// <motivation>
87// Make it possible to lock files in a standard way.
88// </motivation>
89
90
92{
93public:
94 // Define the possible lock types.
95 enum LockType {
96 // Acquire a read lock.
98 // Acquire a write lock.
99 Write
100 };
101
102 // Default constructor creates an invalid fd.
104
105 // Construct the FileLocker object for the given file descriptor.
106 // This can be used to lock a segment of the given file.
107 // The segment is given by start and length. Length=0 means till the
108 // end of the file.
109 explicit FileLocker (int fd, uInt start=0, uInt length=0);
110
112
113 // Acquire a write or read lock.
114 // <src>nattempts</src> defines how often it tries to acquire the lock.
115 // A zero value indicates an infinite number of times (i.e. wait until
116 // the lock is acquired).
117 // A positive value means it waits 1 second between each attempt.
118 Bool acquire (LockType = Write, uInt nattempts = 0);
119
120 // Release a lock.
121 // The return status indicates if an error occurred.
123
124 // Test if the file can be locked for read or write.
125 // Optionally the PID of the process holding the lock is returned.
126 // <group>
129 // </group>
130
131 // Test if the process has a lock for read or write on the file.
132 Bool hasLock (LockType = Write) const;
133
134 // Get the fd in use.
135 int fd() const;
136
137 // Get the last error.
138 int lastError() const;
139
140 // Get the message belonging to the last error.
142
143private:
144 int itsFD;
151};
152
153
155{
156 return (type == Write ? itsWriteLocked : itsReadLocked);
157}
158inline int FileLocker::fd() const
159{
160 return itsFD;
161}
162inline int FileLocker::lastError() const
163{
164 return itsError;
165}
166
167
168
169} //# NAMESPACE CASACORE - END
170
171#endif
172
Bool canLock(uInt &pid, LockType=Write)
int lastError() const
Get the last error.
Definition: FileLocker.h:162
Bool itsReadLocked
temporary for SUSE 6.1
Definition: FileLocker.h:149
Bool canLock(LockType=Write)
Test if the file can be locked for read or write.
Bool release()
Release a lock.
int fd() const
Get the fd in use.
Definition: FileLocker.h:158
Bool hasLock(LockType=Write) const
Test if the process has a lock for read or write on the file.
Definition: FileLocker.h:154
LockType
Define the possible lock types.
Definition: FileLocker.h:95
@ Write
Acquire a write lock.
Definition: FileLocker.h:99
@ Read
Acquire a read lock.
Definition: FileLocker.h:97
String lastMessage() const
Get the message belonging to the last error.
Bool acquire(LockType=Write, uInt nattempts=0)
Acquire a write or read lock.
FileLocker(int fd, uInt start=0, uInt length=0)
Construct the FileLocker object for the given file descriptor.
FileLocker()
Default constructor creates an invalid fd.
String: the storage and methods of handling collections of characters.
Definition: String.h:225
this file contains all the compiler specific defines
Definition: mainpage.dox:28
unsigned int uInt
Definition: aipstype.h:51
LatticeExprNode length(const LatticeExprNode &expr, const LatticeExprNode &axis)
2-argument function to get the length of an axis.
bool Bool
Define the standard types used by Casacore.
Definition: aipstype.h:42