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libcurl-thread.3: expand somewhat on the NO_SIGNAL motivation

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Multi-threaded applictions basically MUST set CURLOPT_NO_SIGNAL to 1L to
avoid the risk of getting a SIGPIPE.

Either way, a multi-threaded application that uses libcurl/openssl needs
to have a signhandler for or ignore SIGPIPE on its own.

Based on discussions in #2800
Closes #2904
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Daniel Stenberg 2018-08-21 14:52:17 +02:00
parent 3c7511b92e
commit 1b8ed4ad23
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1 changed files with 9 additions and 3 deletions
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docs/libcurl/libcurl-thread.3
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@ -5,7 +5,7 @@
.\" * | (__| |_| | _ <| |___
.\" * \___|\___/|_| \_\_____|
.\" *
.\" * Copyright (C) 2015 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
.\" * Copyright (C) 2015 - 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
.\" *
.\" * This software is licensed as described in the file COPYING, which
.\" * you should have received as part of this distribution. The terms
@ -79,8 +79,14 @@ all handles. Everything will or might work fine except that timeouts are not
honored during the DNS lookup - which you can work around by building libcurl
with c-ares or threaded-resolver support. c-ares is a library that provides
asynchronous name resolves. On some platforms, libcurl simply will not
function properly multi-threaded unless the \fICURLOPT_NOSIGNAL(3)\fP option is
set.
function properly multi-threaded unless the \fICURLOPT_NOSIGNAL(3)\fP option
is set.
When \fICURLOPT_NOSIGNAL(3)\fP is set to 1L, your application needs to deal
with the risk of a SIGPIPE (that at least the OpenSSL backend can
trigger). Note that setting \fICURLOPT_NOSIGNAL(3)\fP to 0L will not work in a
threaded situation as there will be race where libcurl risks restoring the
former signal handler while another thread should still ignore it.
.IP "Name resolving"
\fBgethostby* functions and other system calls.\fP These functions, provided
by your operating system, must be thread safe. It is very important that