[OpenSPARC-T2-DV] / tools / perl-5.8.0 / doc / MHonArc / resources / lockmethod.html

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<head>
<title>MHonArc Resources: LOCKMETHOD</title>
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<td align="left" width="50%">[Prev:&nbsp;<a href="lockfile.html">LOCKFILE</a>]</td><td><nobr>[<a href="../resources.html#lockmethod">Resources</a>][<a href="../mhonarc.html">TOC</a>]</nobr></td><td align="right" width="50%">[Next:&nbsp;<a href="locktries.html">LOCKTRIES</a>]</td></tr></table>
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<hr>
<h1>LOCKMETHOD</h1>

<!-- *************************************************************** -->
<hr>
<h2>Syntax</h2>

<dl>

<dt><strong>Envariable</strong></dt>
<dd><p>
<code>M2H_LOCKMETHOD=</code><var>method</var>
</p>
</dd>

<dt><strong>Element</strong></dt>
<dd><p>
<code>&lt;LOCKMETHOD&gt;</code><br>
<var>method</var><br>
<code>&lt;/LOCKMETHOD&gt;</code><br>
</p>
</dd>

<dt><strong>Command-line Option</strong></dt>
<dd><p>
<code>-lockmethod </code><var>method</var>
</p>
</dd>

</dl>

<!-- *************************************************************** -->
<hr>
<h2>Description</h2>

<p>LOCKMETHOD determines how MHonArc should lock archives to protect
multiple MHonArc processes modifying an archive at the same time.  If
after reading this page you still are unsure on what method to use, or
do not understand some of the material, then just stick with the default
value.
</p>

<p>The following is a list of possible values for LOCKMETHOD:
</p>
<dl>

<dt><tt>directory</tt></dt>
<dd><p>MHonArc uses a directory file in the archive directory to
lock an archive.  When MHonArc is to access/modify an archive, it
will first try to create a directory in the archive directory
with a name determined by the
<a href="lockfile.html">LOCKFILE</a> resource.  MHonArc will try
<a href="locktries.html">LOCKTRIES</a> times to create
the directory (obtains the lock) before timing out.
</p>
</dd>

<dt><tt>flock</tt></dt>
<dd><p>MHonArc will use Perl's <b>flock()</b> operator.
<a href="lockfile.html">LOCKFILE</a> will be created in the archive
directory if does not already exist.  Then MHonArc will try to
<a href="locktries.html">LOCKTRIES</a> times to obtain
an exclusive lock on the file via flock() before timing out.
</p>
</dd>

</dl>

<table border=0 cellpadding=4>
<tr valign=top>
<td><strong><font color="red">WARNING</font></strong></td>
<td><p>Each locking method is incompatible with each other.  Therefore,
make sure the same method is specified for all MHonArc processes that
will be accessing a given archive.
If you want to change the default
lock method so it will affect all MHonArc processes, you can set
it via the default resource file or through <b><tt>mhasiteinit.pl</tt></b>.
See
<a href="../install.html#postinstall">Post Installation Configuration</a>
for more information.
</p>
</td>
</tr>
</table>

<p>The following sub-sections give more information of each lock method,
including the pros and cons of each,
and assumes you have some knowledge about file systems.
</p>

<h3>Directory File Method</h3>
<p>The directory file method is the default method used by MHonArc,
and is the method used by past version of MHonArc.  If you are familiar
with locking methods used by other software, you may find it strange
that a directory (which is just a special kind of file) is used instead
of a plain file.  The reason a directory is used is that it has
unique properties over regular files on the various operating systems
MHonArc runs on.  The property that MHonArc takes advantage of is
that you cannot create a new directory over an existing directory of
the same name.  This property is not guaranteed for plain files, or
at least Perl cannot give a common interface for plain files to work
on all platforms.  It may be possible to use a plain file with
Perl's <b>sysopen()</b> operator with the proper options, but
the needed sysopen() options are not guaranteed to be available
for all ports of Perl.
</p>

<h4>Pros</h4>
<ul>
<li><p>Appears to work for all known platforms.
</p>
</li>
</ul>
<h4>Cons</h4>
<ul>
<li><p>If MHonArc/Perl abnormally terminates, MHonArc may not have the
chance to delete the directory, failing to release the lock on the archive
(a stale lock).
This will cause other MHonArc processes to fail out with "Unable to lock ..."
messages.  To correct, manual deletion of the directory is required
(or <a href="force.html">FORCE</a> must be used).
</p>
</li>
</ul>

<h3>flock Method</h3>
<p>Using flock() is a common method for locking files under Unix-type
operating systems.  In order to use flock() method, the <b>Symbol</b>
and <b>Fcntl</b> Perl modules must be available.  If not available, and
this method is specified, MHonArc will fallback to the directory file
method.
</p>
<p>Unlike the directory method, it is okay if
<a href="lockfile.html">LOCKFILE</a> stays around, and actually, it
should never be manual deleted.
</p>

<h4>Pros</h4>
<ul>
<li><p>Lock is automatically released if MHonArc/Perl abnormally terminates,
eliminating the stale lock problem.
</p>
</li>
</ul>
<h4>Cons</h4>
<ul>
<li><p>Not availabe on all platforms.
</p>
</li>
<li><p>May not work over NFS reliably.  Read the documentation
for flock() in the Perl documentation for more information.
</p>
</ul>

<!-- *************************************************************** -->
<hr>
<h2>Default Setting</h2>

<p><tt>directory</tt>
</p>
<table border=0 cellpadding=4>
<tr valign=top>
<td><strong>NOTE</strong></td>
<td><p>The use of &lt;LOCKMETHOD&gt; within an
<a href="rcfile.html">RCFILE</a> will take affect <b>ONLY</b> if used in the
<a href="defrcfile.html">DEFRCFILE</a>.
</p>
</td>
</tr>
</table>
<table border=0 cellpadding=4>
<tr valign=top>
<td><strong><font color="red">WARNING</font></strong></td>
<td><p>Each locking method is incompatible with each other.  Therefore,
make sure the same method is specified for all MHonArc processes that
will be accessing a given archive.
If you want to change the default
lock method so it will affect all MHonArc processes, you can set
it via the default resource file or through <b><tt>mhasiteinit.pl</tt></b>.
See
<a href="../install.html#postinstall">Post Installation Configuration</a>
for more information.
</p>
</td>
</tr>
</table>


<!-- *************************************************************** -->
<hr>
<h2>Resource Variables</h2>

<p>N/A
</p>

<!-- *************************************************************** -->
<hr>
<h2>Examples</h2>

<p>None.
</p>

<!-- *************************************************************** -->
<hr>
<h2>Version</h2>

<p>2.4.0
</p>

<!-- *************************************************************** -->
<hr>
<h2>See Also</h2>

<p>
<a href="force.html">FORCE</a>,
<a href="lock.html">LOCK</a>,
<a href="lockdelay.html">LOCKDELAY</a>,
<a href="lockfile.html">LOCKFILE</a>,
<a href="locktries.html">LOCKTRIES</a>
</p>

<!-- *************************************************************** -->
<hr>
<!--x-rc-nav-->
<table border=0><tr valign="top">
<td align="left" width="50%">[Prev:&nbsp;<a href="lockfile.html">LOCKFILE</a>]</td><td><nobr>[<a href="../resources.html#lockmethod">Resources</a>][<a href="../mhonarc.html">TOC</a>]</nobr></td><td align="right" width="50%">[Next:&nbsp;<a href="locktries.html">LOCKTRIES</a>]</td></tr></table>
<!--/x-rc-nav-->
<hr>
<address>
$Date: 2002/07/27 05:13:10 $ <br>
<img align="top" src="../monicon.png" alt="">
<a href="http://www.mhonarc.org/"
><strong>MHonArc</strong></a><br>
Copyright &#169; 1999, <a href="http://www.earlhood.com/"
>Earl Hood</a>, <a href="mailto:mhonarc@mhonarc.org"
>mhonarc@mhonarc.org</a><br>
</address>

</body>
</html>
Commit	Line	Data
86530b38 AT	1	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML//EN">
	2	<html>
	3	<head>
	4	<title>MHonArc Resources: LOCKMETHOD</title>
	5	</head>
	6	<body>
	7	<!--x-rc-nav-->
	8	<table border=0><tr valign="top">
	9	<td align="left" width="50%">[Prev: <a href="lockfile.html">LOCKFILE</a>]</td><td><nobr>[<a href="../resources.html#lockmethod">Resources</a>][<a href="../mhonarc.html">TOC</a>]</nobr></td><td align="right" width="50%">[Next: <a href="locktries.html">LOCKTRIES</a>]</td></tr></table>
	10	<!--/x-rc-nav-->
	11	<hr>
	12	<h1>LOCKMETHOD</h1>
	13
	14	<!-- *************************************************************** -->
	15	<hr>
	16	<h2>Syntax</h2>
	17
	18	<dl>
	19
	20	<dt><strong>Envariable</strong></dt>
	21	<dd><p>
	22	<code>M2H_LOCKMETHOD=</code><var>method</var>
	23	</p>
	24	</dd>
	25
	26	<dt><strong>Element</strong></dt>
	27	<dd><p>
	28	<code><LOCKMETHOD></code><br>
	29	<var>method</var><br>
	30	<code></LOCKMETHOD></code><br>
	31	</p>
	32	</dd>
	33
	34	<dt><strong>Command-line Option</strong></dt>
	35	<dd><p>
	36	<code>-lockmethod </code><var>method</var>
	37	</p>
	38	</dd>
	39
	40	</dl>
	41
	42	<!-- *************************************************************** -->
	43	<hr>
	44	<h2>Description</h2>
	45
	46	<p>LOCKMETHOD determines how MHonArc should lock archives to protect
	47	multiple MHonArc processes modifying an archive at the same time. If
	48	after reading this page you still are unsure on what method to use, or
	49	do not understand some of the material, then just stick with the default
	50	value.
	51	</p>
	52
	53	<p>The following is a list of possible values for LOCKMETHOD:
	54	</p>
	55	<dl>
	56
	57	<dt><tt>directory</tt></dt>
	58	<dd><p>MHonArc uses a directory file in the archive directory to
	59	lock an archive. When MHonArc is to access/modify an archive, it
	60	will first try to create a directory in the archive directory
	61	with a name determined by the
	62	<a href="lockfile.html">LOCKFILE</a> resource. MHonArc will try
	63	<a href="locktries.html">LOCKTRIES</a> times to create
	64	the directory (obtains the lock) before timing out.
65	</p>
66	</dd>
67
68	<dt><tt>flock</tt></dt>
69	<dd><p>MHonArc will use Perl's <b>flock()</b> operator.
70	<a href="lockfile.html">LOCKFILE</a> will be created in the archive
71	directory if does not already exist. Then MHonArc will try to
72	<a href="locktries.html">LOCKTRIES</a> times to obtain
73	an exclusive lock on the file via flock() before timing out.
74	</p>
75	</dd>
76
77	</dl>
78
79	<table border=0 cellpadding=4>
80	<tr valign=top>
81	<td><strong><font color="red">WARNING</font></strong></td>
82	<td><p>Each locking method is incompatible with each other. Therefore,
83	make sure the same method is specified for all MHonArc processes that
84	will be accessing a given archive.
85	If you want to change the default
86	lock method so it will affect all MHonArc processes, you can set
87	it via the default resource file or through <b><tt>mhasiteinit.pl</tt></b>.
88	See
89	<a href="../install.html#postinstall">Post Installation Configuration</a>
90	for more information.
91	</p>
92	</td>
93	</tr>
94	</table>
95
96	<p>The following sub-sections give more information of each lock method,
97	including the pros and cons of each,
98	and assumes you have some knowledge about file systems.
99	</p>
100
101	<h3>Directory File Method</h3>
102	<p>The directory file method is the default method used by MHonArc,
103	and is the method used by past version of MHonArc. If you are familiar
104	with locking methods used by other software, you may find it strange
105	that a directory (which is just a special kind of file) is used instead
106	of a plain file. The reason a directory is used is that it has
107	unique properties over regular files on the various operating systems
108	MHonArc runs on. The property that MHonArc takes advantage of is
109	that you cannot create a new directory over an existing directory of
110	the same name. This property is not guaranteed for plain files, or
111	at least Perl cannot give a common interface for plain files to work
112	on all platforms. It may be possible to use a plain file with
113	Perl's <b>sysopen()</b> operator with the proper options, but
114	the needed sysopen() options are not guaranteed to be available
115	for all ports of Perl.
116	</p>
117
118	<h4>Pros</h4>
119	<ul>
120	<li><p>Appears to work for all known platforms.
121	</p>
122	</li>
123	</ul>
124	<h4>Cons</h4>
125	<ul>
126	<li><p>If MHonArc/Perl abnormally terminates, MHonArc may not have the
127	chance to delete the directory, failing to release the lock on the archive
128	(a stale lock).
129	This will cause other MHonArc processes to fail out with "Unable to lock ..."
130	messages. To correct, manual deletion of the directory is required
131	(or <a href="force.html">FORCE</a> must be used).
132	</p>
133	</li>
134	</ul>
135
136	<h3>flock Method</h3>
137	<p>Using flock() is a common method for locking files under Unix-type
138	operating systems. In order to use flock() method, the <b>Symbol</b>
139	and <b>Fcntl</b> Perl modules must be available. If not available, and
140	this method is specified, MHonArc will fallback to the directory file
141	method.
142	</p>
143	<p>Unlike the directory method, it is okay if
144	<a href="lockfile.html">LOCKFILE</a> stays around, and actually, it
145	should never be manual deleted.
146	</p>
147
148	<h4>Pros</h4>
149	<ul>
150	<li><p>Lock is automatically released if MHonArc/Perl abnormally terminates,
151	eliminating the stale lock problem.
152	</p>
153	</li>
154	</ul>
155	<h4>Cons</h4>
156	<ul>
157	<li><p>Not availabe on all platforms.
158	</p>
159	</li>
160	<li><p>May not work over NFS reliably. Read the documentation
161	for flock() in the Perl documentation for more information.
162	</p>
163	</ul>
164
165	<!-- *************************************************************** -->
166	<hr>
167	<h2>Default Setting</h2>
168
169	<p><tt>directory</tt>
170	</p>
171	<table border=0 cellpadding=4>
172	<tr valign=top>
173	<td><strong>NOTE</strong></td>
174	<td><p>The use of <LOCKMETHOD> within an
175	<a href="rcfile.html">RCFILE</a> will take affect <b>ONLY</b> if used in the
176	<a href="defrcfile.html">DEFRCFILE</a>.
177	</p>
178	</td>
179	</tr>
180	</table>
181	<table border=0 cellpadding=4>
182	<tr valign=top>
183	<td><strong><font color="red">WARNING</font></strong></td>
184	<td><p>Each locking method is incompatible with each other. Therefore,
185	make sure the same method is specified for all MHonArc processes that
186	will be accessing a given archive.
187	If you want to change the default
188	lock method so it will affect all MHonArc processes, you can set
189	it via the default resource file or through <b><tt>mhasiteinit.pl</tt></b>.
190	See
191	<a href="../install.html#postinstall">Post Installation Configuration</a>
192	for more information.
193	</p>
194	</td>
195	</tr>
196	</table>
197
198
199	<!-- *************************************************************** -->
200	<hr>
201	<h2>Resource Variables</h2>
202
203	<p>N/A
204	</p>
205
206	<!-- *************************************************************** -->
207	<hr>
208	<h2>Examples</h2>
209
210	<p>None.
211	</p>
212
213	<!-- *************************************************************** -->
214	<hr>
215	<h2>Version</h2>
216
217	<p>2.4.0
218	</p>
219
220	<!-- *************************************************************** -->
221	<hr>
222	<h2>See Also</h2>
223
224	<p>
225	<a href="force.html">FORCE</a>,
226	<a href="lock.html">LOCK</a>,
227	<a href="lockdelay.html">LOCKDELAY</a>,
228	<a href="lockfile.html">LOCKFILE</a>,
229	<a href="locktries.html">LOCKTRIES</a>
230	</p>
231
232	<!-- *************************************************************** -->
233	<hr>
234	<!--x-rc-nav-->
235	<table border=0><tr valign="top">
236	<td align="left" width="50%">[Prev: <a href="lockfile.html">LOCKFILE</a>]</td><td><nobr>[<a href="../resources.html#lockmethod">Resources</a>][<a href="../mhonarc.html">TOC</a>]</nobr></td><td align="right" width="50%">[Next: <a href="locktries.html">LOCKTRIES</a>]</td></tr></table>
237	<!--/x-rc-nav-->
238	<hr>
239	<address>
240	$Date: 2002/07/27 05:13:10 $ <br>
241	<img align="top" src="../monicon.png" alt="">
242	<a href="http://www.mhonarc.org/"
243	><strong>MHonArc</strong></a><br>
244	Copyright © 1999, <a href="http://www.earlhood.com/"
245	>Earl Hood</a>, <a href="mailto:mhonarc@mhonarc.org"
246	>mhonarc@mhonarc.org</a><br>
247	</address>
248
249	</body>
250	</html>