Some assertions and comments in scheduler

Test Plan:
I can't validate this because of existing errors with the debug runtime. I'll
see if this introduces any new failures.

Reviewers: simonmar, bgamari, erikd

Reviewed By: simonmar

Subscribers: rwbarton, carter

Differential Revision: https://phabricator.haskell.org/D5337

1 files changed, 4 insertions, 1 deletions

diff --git a/rts/Capability.h b/rts/Capability.h
index 250ec2219c..05a827c7b9 100644
--- a/rts/Capability.h
+++ b/rts/Capability.h
@@ -264,7 +264,10 @@ typedef enum {
 //
 typedef struct {
     SyncType type;              // The kind of synchronisation
-    bool *idle;
+    bool *idle;                 // Array of size n_capabilities. idle[i] is true
+                                // if capability i will be idle during this GC
+                                // cycle. Only available when doing GC (when
+                                // type is SYNC_GC_*).
     Task *task;                 // The Task performing the sync
 } PendingSync;