From: Job Snijders <job@openbsd.org>
Subject: mention mutex in pthread_cond_init.3?
To: tech@openbsd.org
Date: Fri, 20 Jun 2025 13:25:15 +0000

Dear Guehnther / Tedu,

As I understand it, a mutex must be used to protect the condition
variable itself. So I think the below might help clarify the
relationship between conditions and mutexes. OK?

Index: ./man/pthread_cond_init.3
===================================================================
RCS file: /cvs/src/lib/libpthread/man/pthread_cond_init.3,v
diff -u -p -r1.13 pthread_cond_init.3
--- ./man/pthread_cond_init.3	7 Jun 2025 00:16:52 -0000	1.13
+++ ./man/pthread_cond_init.3	20 Jun 2025 13:20:56 -0000
@@ -50,6 +50,8 @@ If
 is
 .Dv NULL ,
 the default attributes are used.
+.Pp
+A condition variable must always be used in conjunction with a mutex.
 .Sh RETURN VALUES
 If successful, the
 .Fn pthread_cond_init
@@ -76,7 +78,8 @@ variable.
 .Xr pthread_cond_destroy 3 ,
 .Xr pthread_cond_signal 3 ,
 .Xr pthread_cond_timedwait 3 ,
-.Xr pthread_cond_wait 3
+.Xr pthread_cond_wait 3 ,
+.Xr pthread_mutex_init 3
 .Sh STANDARDS
 .Fn pthread_cond_init
 conforms to