docs: note strict sequential ordering of MVar operations

[ghc-base.git] / Control / Concurrent / MVar.hs

diff --git a/Control/Concurrent/MVar.hs b/Control/Concurrent/MVar.hs
index 3a38294..2fda9f7 100644 (file)
--- a/Control/Concurrent/MVar.hs
+++ b/Control/Concurrent/MVar.hs
@@ -61,6 +61,13 @@
 -- in an 'MVar' to the appropriate normal form, or utilize a strict
 -- MVar provided by the strict-concurrency package.
 --
+-- * Ordering
+--
+-- 'MVar' operations are always observed to take place in the order
+-- they are written in the program, regardless of the memory model of
+-- the underlying machine.  This is in contrast to 'IORef' operations
+-- which may appear out-of-order to another thread in some cases.
+--
 -- * Example
 --
 -- Consider the following concurrent data structure, a skip channel.