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8 <title>Apache 2.0 Thread Safe Issues</title>
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16 <h1>Thread Safetyness</h1>
17 <p>When using any of the threaded mpms in Apache 2.0 it is important
18 that every function from Apache be thread safe. When linking in 3rd
19 party extensions it can be difficult to determine whether the resulting
20 server will be thread safe. Casual testing generally won't tell you this
21 either as thread safety problems can lead to subtle race conditons that
22 may only show up in certain conditions under heavy load.</p>
24 <h1>Common 3rd Party Libraries</h1>
25 <p>The following is a list of common libraries that are used by 3rd party
26 Apache modules. You can check to see if your module is using a potentially
27 unsafe library by using tools such as <tt>ldd</tt> and <tt>nm</tt>. For PHP,
28 for example, try this:
30 libsablot.so.0 => /usr/local/lib/libsablot.so.0 (0x401f6000)
31 libexpat.so.0 => /usr/lib/libexpat.so.0 (0x402da000)
32 libsnmp.so.0 => /usr/lib/libsnmp.so.0 (0x402f9000)
33 libpdf.so.1 => /usr/local/lib/libpdf.so.1 (0x40353000)
34 libz.so.1 => /usr/lib/libz.so.1 (0x403e2000)
35 libpng.so.2 => /usr/lib/libpng.so.2 (0x403f0000)
36 libmysqlclient.so.11 => /usr/lib/libmysqlclient.so.11 (0x40411000)
37 libming.so => /usr/lib/libming.so (0x40449000)
38 libm.so.6 => /lib/libm.so.6 (0x40487000)
39 libfreetype.so.6 => /usr/lib/libfreetype.so.6 (0x404a8000)
40 libjpeg.so.62 => /usr/lib/libjpeg.so.62 (0x404e7000)
41 libcrypt.so.1 => /lib/libcrypt.so.1 (0x40505000)
42 libssl.so.2 => /lib/libssl.so.2 (0x40532000)
43 libcrypto.so.2 => /lib/libcrypto.so.2 (0x40560000)
44 libresolv.so.2 => /lib/libresolv.so.2 (0x40624000)
45 libdl.so.2 => /lib/libdl.so.2 (0x40634000)
46 libnsl.so.1 => /lib/libnsl.so.1 (0x40637000)
47 libc.so.6 => /lib/libc.so.6 (0x4064b000)
48 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x80000000)</pre>
49 In addition to these libraries you will need to have a look at any libraries
50 linked statically into the module. You can use <tt>nm</tt> to look for individual
51 symbols in the module.</p>
54 <p>Please drop a note to rasmus@apache.org [need a better contact address here] if
55 you have additions or corrections to this list.</p>
57 <table><tr><th>Library</th><th>Version</th><th>Thread Safe?</th><th>Notes</th></tr>
58 <tr><td><a href="http://aspell.sourceforge.net/">ASpell/PSpell</a></td><td> </td><td>?</td><td> </td></tr>
59 <tr><td><a href="http://www.sleepycat.com/">Berkeley DB</a></td><td> </td><td>?</td><td> </td></tr>
60 <tr><td><a href="http://sources.redhat.com/bzip2/index.html">BZip2</a></td><td> </td><td>?</td><td> </td></tr>
61 <tr><td><a href="http://cr.yp.to/cdb.html">cdb</a></td><td> </td><td>?</td><td> </td></tr>
62 <tr><td><a href="http://www.washington.edu/imap/">C-Client</a></td><td> </td><td>?</td><td> </td></tr>
63 <tr><td><a href="http://www.fastio.com/">cpdflib</a></td><td> </td><td>?</td><td> </td></tr>
64 <tr><td><a href="http://www.ijg.org/files/">libcrypt</a></td><td> </td><td>?</td><td> </td></tr>
65 <tr><td>Expat</td><td> </td><td>Yes</td><td>Need a separate parser instance per thread</td></tr>
66 <tr><td><a href="http://www.freetds.org/">FreeTDS</a></td><td> </td><td>?</td><td> </td></tr>
67 <tr><td><a href="http://www.freetype.org/">FreeType</a></td><td> </td><td>?</td><td> </td></tr>
68 <tr><td><a href="http://www.boutell.com/gd/">GD 1.8.x</a></td><td> </td><td>?</td><td> </td></tr>
69 <tr><td><a href="http://www.boutell.com/gd/">GD 2.0.x</a></td><td> </td><td>?</td><td> </td></tr>
70 <tr><td><a href="http://www.gnu.org/software/gdbm/gdbm.html">gdbm</a></td><td> </td><td>?</td><td> </td></tr>
71 <tr><td><a href="http://www.imagemagick.org/">ImageMagick</a></td><td> </td><td>?</td><td> </td></tr>
72 <tr><td><a href="http://www.enlightenment.org/pages/imlib2.html">Imlib2</a></td><td> </td><td>?</td><td> </td></tr>
73 <tr><td><a href="http://www.ijg.org/files/">libjpeg</a></td><td>v6b</td><td>?</td><td> </td></tr>
74 <tr><td><a href="http://mysql.com">libmysqlclient</a></td><td> </td><td>?</td><td> </td></tr>
75 <tr><td><a href="http://www.opaque.net/ming/">Ming</a></td><td>0.2a</td><td>?</td><td> </td></tr>
76 <tr><td><a href="http://net-snmp.sourceforge.net/">Net-SNMP</a></td><td>5.0.x</td><td>?</td><td> </td></tr>
77 <tr><td><a href="http://www.openldap.org/">OpenLDAP</a></td><td>2.1.x</td><td>?</td><td> </td></tr>
78 <tr><td><a href="http://www.openssl.org/">OpenSSL</a></td><td>0.96g</td><td>?</td><td> </td></tr>
79 <tr><td><a href="http://www.oracle.com/">liboci8 (Oracle 8+)</a></td><td>8.x,9.x</td><td>?</td><td> </td></tr>
80 <tr><td><a href="http://pdflib.com/">pdflib</a></td><td>4.0.x</td><td>?</td><td> </td></tr>
81 <tr><td><a href="http://www.libpng.org/pub/png/libpng.html">libpng</a></td><td>1.0.x</td><td>?</td><td> </td></tr>
82 <tr><td><a href="http://www.libpng.org/pub/png/libpng.html">libpng</a></td><td>1.2.x</td><td>?</td><td> </td></tr>
83 <tr><td><a href="http://www.postgresql.org/idocs/index.php?libpq-threading.html">libpq (PostgreSQL)</a></td><td>7.x</td><td>Yes</td><td>Don't share connections across threads and watch out for crypt() calls</td></tr>
84 <tr><td><a href="http://www.gingerall.com/charlie/ga/xml/p_sab.xml">Sablotron</a></td><td>0.95</td><td>?</td><td> </td></tr>
85 <tr><td><a href="http://www.gzip.org/zlib/">zlib</a></td><td>1.1.4</td><td>?</td><td> </td></tr>
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