+ /* multiple_threads is enabled either when the process has spawned at
+ least one thread or when a single-threaded process cancels itself.
+ This enables additional code to introduce locking before doing some
+ compare_and_exchange operations and also enable cancellation points.
+ The concepts of multiple threads and cancellation points ideally
+ should be separate, since it is not necessary for multiple threads to
+ have been created for cancellation points to be enabled, as is the
+ case is when single-threaded process cancels itself.
+
+ Since enabling multiple_threads enables additional code in
+ cancellation points and compare_and_exchange operations, there is a
+ potential for an unneeded performance hit when it is enabled in a
+ single-threaded, self-canceling process. This is OK though, since a
+ single-threaded process will enable async cancellation only when it
+ looks to cancel itself and is hence going to end anyway. */