concurrency.md

@@ -52,7 +52,16 @@ necessarily 'concurrent reentrant' ones.
 - if any haskell thread is runnable then at least one thread will be running.
 - foreign calls marked 'concurrent' will not interfere will the above rule.
 
-## MVar Guarentees
+
+Additionally, we have a fairness property of `MVar`s:
+
+- A thread blocked on an `MVar` will eventually run, provided there are no other
+  threads holding the `MVar` indefinitely.
+
+
+This means that `MVar` blocking must be implemented in a fair way, eg. a FIFO of blocked threads.
+
+## `MVar` Guarentees
 
 
 initial proposal is here: