From: ianmdlvl <ianmdlvl>
Date: Sun, 13 Jul 2003 22:51:47 +0000 (+0000)
Subject: improve deadlock section
X-Git-Tag: rel-4-0-0~2
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=chiark-utils.git;a=commitdiff_plain;h=78ad6d7c4fcfc77d83649a4082a8dae4359bdbf1

improve deadlock section
---

diff --git a/cprogs/with-lock-ex.1 b/cprogs/with-lock-ex.1
index f83f263..ce3f87f 100644
--- a/cprogs/with-lock-ex.1
+++ b/cprogs/with-lock-ex.1
@@ -56,6 +56,30 @@ which a process might lock simultaneously, either
 or
 .IR B > A
 where the relation > is transitive and noncyclic.
+.PP
+Then, for any two locks
+.I X
+and
+.I Y
+with
+.IR X > Y
+it is forbidden to acquire
+.I X
+while holding
+.IR Y .
+Instead, acquire
+.I X
+first, or release
+.I Y
+before (re)acquiring
+.I X
+and
+.I Y
+in that order.
+.PP
+(There are more complicated ways of avoiding deadlocks, but a lock
+hierarchy is simple to understand and implement.  If it does not meet
+your needs, consult the literature.)
 .SH LOCKING PROTOCOL
 The locking protocol used by
 .B with-lock-ex