git: 934a35ac2bbb - main - libthr.3: describe SIGTHR

The branch main has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=934a35ac2bbbcf8cd65d8824fa824eb5c6170c88

commit 934a35ac2bbbcf8cd65d8824fa824eb5c6170c88
Author:     Konstantin Belousov <kib@FreeBSD.org>
AuthorDate: 2026-04-13 23:42:51 +0000
Commit:     Konstantin Belousov <kib@FreeBSD.org>
CommitDate: 2026-04-14 12:51:38 +0000

    libthr.3: describe SIGTHR
    
    Explain how SIGTHR is used and that it should be not touched by user
    code.  Note about SIGLIBRT.
    
    Reviewed by:    emaste
    Sponsored by:   The FreeBSD Foundation
    MFC after:      3 days
    Differential revision:  https://reviews.freebsd.org/D56384
---
 lib/libthr/libthr.3 | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/lib/libthr/libthr.3 b/lib/libthr/libthr.3
index 8c7b84490547..5d9c5ec6706b 100644
--- a/lib/libthr/libthr.3
+++ b/lib/libthr/libthr.3
@@ -269,6 +269,25 @@ the critical section.
 This should be taken into account when interpreting
 .Xr ktrace 1
 logs.
+.Pp
+The
+.Nm
+library uses the
+.Va SIGTHR
+signal for internal operations, in particular,
+for cancellation requests.
+This signal's masking and disposition is controlled by the library,
+and user programs should not try to modify them.
+The library interposes functions controlling signals to prevent
+inadvertent modifications and to guard portable code against
+exposure to
+.Va SIGTHR .
+.Pp
+Note: similarly, the
+.Va SIGLIBRT
+signal is reserved for use by
+.Lb librt ,
+and should be not modified by users.
 .Sh PROCESS-SHARED SYNCHRONIZATION OBJECTS
 In the
 .Li libthr