add multi-thread details for GnuTLS

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.TH libcurl-tutorial 3 "25 Jan 2005" "libcurl" "libcurl programming"

.TH libcurl-tutorial 3 "9 May 2005" "libcurl" "libcurl programming"

.SH NAME

libcurl-tutorial \- libcurl programming tutorial

.SH "Objective"

previous

.SH "Multi-threading Issues"

libcurl is completely thread safe, except for two issues: signals and alarm

handlers. Signals are needed for a SIGPIPE handler, and the alarm() call is

used to deal with timeouts (during DNS lookup).

The first basic rule is that you must \fBnever\fP share a libcurl handle (be

it easy or multi or whatever) between multiple threads. Only use one handle in

one thread at a time.

libcurl is completely thread safe, except for two issues: signals and SSL/TLS

handlers. Signals are used timeouting name resolves (during DNS lookup) - when

built without c-ares support and not on Windows..

If you are accessing HTTPS or FTPS URLs in a multi-threaded manner, you are

then of course using OpenSSL multi-threaded and it has itself a few

requirements on this. Basically, you need to provide one or two functions to

allow it to function properly. For all details, see this:

then of course using OpenSSL/GnuTLS multi-threaded and those libs have their

own requirements on this issue. Basically, you need to provide one or two

functions to allow it to function properly. For all details, see this:

OpenSSL

   http://www.openssl.org/docs/crypto/threads.html#DESCRIPTION

GnuTLS

 http://www.gnu.org/software/gnutls/manual/html_node/Multi_002dthreaded-applications.html

When using multiple threads you should set the CURLOPT_NOSIGNAL option to

TRUE for all handles. Everything will work fine except that timeouts are not

honored during the DNS lookup - which you can work around by building libcurl