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Added information about locking

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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@104338 c90b9560-bf6c-de11-be94-00142212c4b1
This commit is contained in:
Marcus Boerger 2002-11-15 17:31:32 +00:00
parent 1c69193a3d
commit 8aca0e3c47
1 changed files with 98 additions and 6 deletions
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104
reference/dba/functions/dba-open.xml
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@ -1,5 +1,5 @@
<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.6 $ -->
<!-- $Revision: 1.7 $ -->
<!-- splitted from ./en/functions/dba.xml, last change in rev 1.2 -->
<refentry id="function.dba-open">
<refnamediv>
@ -27,7 +27,11 @@
<parameter>mode</parameter> is "r" for read access, "w" for read/write
access to an already existing database, "c" for read/write access
and database creation if it doesn't currently exist, and "n" for
create, truncate and read/write access.
create, truncate and read/write access. Additional you can use "l" to
lock the database with an .lck file or "d" to lock the databasefile itself.
It is important that all of your applications do this consistently. If
you want to test the access and do not want to wait for the lock you can
add "t".
</para>
<para>
<parameter>handler</parameter> is the <link linkend="dba.requirements">name
@ -44,10 +48,98 @@
<para>
There can only be one writer for one database file. When you use dba on
a webserver and more than one request requires write operations they can
only be done one after another. Unfortuanetly some of the external
libraries simply fail or ignore this when trying to open the database for
another write operation. In this case you must use semaphores to guard
against. See <link linkend="ref.sem">System V semaphore support</link>.
only be done one after another. Also read during write is not allowed.
The dba extension uses locks to prevent this. See the follwoing table:
<table>
<title>DBA locking</title>
<tgroup cols="9">
<thead>
<row>
<entry>already open</entry>
<entry><parameter>mode</parameter> = "rl"</entry>
<entry><parameter>mode</parameter> = "rlt"</entry>
<entry><parameter>mode</parameter> = "wl"</entry>
<entry><parameter>mode</parameter> = "wlt"</entry>
<entry><parameter>mode</parameter> = "rd"</entry>
<entry><parameter>mode</parameter> = "rdt"</entry>
<entry><parameter>mode</parameter> = "wd"</entry>
<entry><parameter>mode</parameter> = "wdt"</entry>
</row>
</thead>
<tbody>
<row>
<entry>not open</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>ok</entry>
</row>
<row>
<entry><parameter>mode</parameter> = "rl"</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>wait</entry>
<entry>false</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
</row>
<row>
<entry><parameter>mode</parameter> = "wl"</entry>
<entry>wait</entry>
<entry>false</entry>
<entry>wait</entry>
<entry>false</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
</row>
<row>
<entry><parameter>mode</parameter> = "rd"</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>wait</entry>
<entry>false</entry>
</row>
<row>
<entry><parameter>mode</parameter> = "wd"</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>wait</entry>
<entry>false</entry>
<entry>wait</entry>
<entry>false</entry>
</row>
</tbody>
</tgroup>
</table>
<simplelist>
<member>ok: the second call will be successfull.</member>
<member>wait: the second call waits until <function>dba_close</function> is called for the first.</member>
<member>false: the second call returns false.</member>
<member>illegal: you must not mix "l" and "d" modifiers for <parameter>mode</parameter> parameter.</member>
</simplelist>
</para>
</note>
<note>
<para>
Locking and the <parameter>mode</parameter> modifiers "l", "d" and "t" were
added in PHP 4.3.0.
In PHP versions before PHP 4.3.0 you must use semaphores to guard against
simultanious database access for any database handler with the exception of
GDBM. See <link linkend="ref.sem">System V semaphore support</link>.
</para>
</note>
<para>