helly Fri Nov 15 12:31:33 2002 EDT
Modified files:
/phpdoc/en/reference/dba/functions dba-open.xml
Log:
Added information about locking
Index: phpdoc/en/reference/dba/functions/dba-open.xml
diff -u phpdoc/en/reference/dba/functions/dba-open.xml:1.6
phpdoc/en/reference/dba/functions/dba-open.xml:1.7
--- phpdoc/en/reference/dba/functions/dba-open.xml:1.6 Sun Nov 10 18:22:27 2002
+++ phpdoc/en/reference/dba/functions/dba-open.xml Fri Nov 15 12:31:32 2002
@@ -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>
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