The function getlogin() is not thread safe.

Signed-off-by: Peng Haitao <redacted>
---
 man3/getlogin.3 | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/man3/getlogin.3 b/man3/getlogin.3
index be7cc87..4a2a3e9 100644
--- a/man3/getlogin.3
+++ b/man3/getlogin.3

@@ -135,6 +135,19 @@ password database file
 \fI/var/run/utmp\fP
 (traditionally \fI/etc/utmp\fP;
 some libc versions used \fI/var/adm/utmp\fP)
+.SH ATTRIBUTES
+.SS Multithreading(see pthreads(7))
+The
+.BR getlogin ()
+function is not thread-safe.
+.LP
+The
+.BR getlogin_r ()
+function is thread-safe.
+.LP
+The
+.BR cuserid ()
+function is thread-safe with exceptions.