libcurl-thread.3: improved name resolver wording

And make better .SH sections

Closes #10966

diff --git a/docs/libcurl/libcurl-thread.3 b/docs/libcurl/libcurl-thread.3
index a29c4e821d9e75224acca94421d81e5d2e4b7df1..5c189de459344bb9918497b329d40fc3036cf2f1 100644 (file)
--- a/docs/libcurl/libcurl-thread.3
+++ b/docs/libcurl/libcurl-thread.3
@@ -30,13 +30,17 @@ libcurl is thread safe but has no internal thread synchronization. You may have
 to provide your own locking should you meet any of the thread safety exceptions
 below.
 
-\fBHandles.\fP You must \fBnever\fP share the same handle in multiple threads.
-You can pass the handles around among threads, but you must never use a single
-handle from more than one thread at any given time.
-
-\fBShared objects.\fP You can share certain data between multiple handles by
-using the share interface but you must provide your own locking and set
+.SH "Handles"
+You must \fBnever\fP share the same handle in multiple threads.  You can pass
+the handles around among threads, but you must never use a single handle from
+more than one thread at any given time.
+.SH "Shared objects"
+You can share certain data between multiple handles by using the share
+interface but you must provide your own locking and set
 \fIcurl_share_setopt(3)\fP CURLSHOPT_LOCKFUNC and CURLSHOPT_UNLOCKFUNC.
+
+Note that some items are specifically documented as not thread-safe in the
+share API (the connection pool and HSTS cache for example).
 .SH TLS
 If you are accessing HTTPS or FTPS URLs in a multi-threaded manner, you are
 then of course using the underlying SSL library multi-threaded and those libs
@@ -69,8 +73,7 @@ The engine is used by libcurl in a way that is fully thread-safe.
 The engine is used by libcurl in a way that is fully thread-safe.
 .IP AWS-LC
 The engine is used by libcurl in a way that is fully thread-safe.
-.SH "Other areas of caution"
-.IP Signals
+.SH "Signals"
 Signals are used for timing out name resolves (during DNS lookup) - when built
 without using either the c-ares or threaded resolver backends. When using
 multiple threads you should set the \fICURLOPT_NOSIGNAL(3)\fP option to 1L for
@@ -86,16 +89,17 @@ 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 important that libcurl
-can find and use thread safe versions of these and other system calls, as
-otherwise it cannot function fully thread safe. Some operating systems are
-known to have faulty thread implementations. We have previously received
-problem reports on *BSD (at least in the past, they may be working fine these
-days). Some operating systems that are known to have solid and working thread
-support are Linux, Solaris and Windows.
-.IP "curl_global_* functions"
+.SH "Name resolving"
+The \fBgethostbyname\fP or \fBgetaddrinfo\fP and other name resolving system
+calls used by libcurl are provided by your operating system and must be thread
+safe. It is important that libcurl can find and use thread safe versions of
+these and other system calls, as otherwise it cannot function fully thread
+safe. Some operating systems are known to have faulty thread
+implementations. We have previously received problem reports on *BSD (at least
+in the past, they may be working fine these days). Some operating systems that
+are known to have solid and working thread support are Linux, Solaris and
+Windows.
+.SH "curl_global_* functions"
 These functions are thread-safe since libcurl 7.84.0 if
 \fIcurl_version_info(3)\fP has the \fBCURL_VERSION_THREADSAFE\fP feature bit
 set (most platforms).
@@ -107,11 +111,11 @@ initialize the library and its dependents, rather than rely on the "lazy"
 fail-safe initialization that takes place the first time
 \fIcurl_easy_init(3)\fP is called. For an in-depth explanation refer to
 \fIlibcurl(3)\fP section \fBGLOBAL CONSTANTS\fP.
-.IP "Memory functions"
+.SH "Memory functions"
 These functions, provided either by your operating system or your own
 replacements, must be thread safe. You can use \fIcurl_global_init_mem(3)\fP
 to set your own replacement memory functions.
-.IP "Non-safe functions"
+.SH "Non-safe functions"
 \fICURLOPT_DNS_USE_GLOBAL_CACHE(3)\fP is not thread-safe.
 
 \fIcurl_version_info(3)\fP is not thread-safe before libcurl initialization.