concurrency.md

@@ -467,6 +467,10 @@ new library calls provided
 
 - `mergeIO`, `nmergeIO`
 
+
+Possibly: define the meaning of using concurrent and/or reentrant foreign calls with `unsafePerformIO` (see below)?
+
+
 ## Optional Feature 2 - OS threads
 
 
@@ -495,9 +499,18 @@ this might be an issue for you.
 
 
 
-Using concurrent operations inside of an unsafePerformIO or unsafeInterleaveIO
-may have unforseen consequences, check an implementations documentation for
-details before depending on any particular behavior.
+The following operations inside `unsafePerformIO` are undefined:
+
+
+- concurrent or reentrant foreign calls
+- I/O operations
+
+
+Additionally, foreign imports that are both declared to return a non-IO type and declared concurrent and/or reentrant are undefined.
+
+
+
+Check an implementation's documentation for details before depending on any particular behavior.
 
 
 # Status of Compilers