A Chez Scheme garbage collection involves a rendezvous among threads
that are used to implement places and futures (and potentially other
things that create Chez-level threads). The thread that is used to
drive the garbage collection was not formerly specified, and callbacks
like the GC icon in DrRacket can only be run in the initial thread.
When a major collection was run in a non-initial thread, the callback
was simply skipped.
The Racket branch of Chez Scheme now drives a collection in the
initial thread whenever that thread is active. In Racket CS, the
initial thread can be inactive if it's waiting for external events,
and a place can meanwhile trigger a GC. Now, when the Racket CS GC
callback is called for a major collection in any thread other than the
initial one, it defers the major collection to an asynchornous
callback in the main thread (and meanwhile performs a minor
collection).
So, a major collection might now be delayed by just a little while if
the main thread is inactive, such as when it's waiting for external
events, but callbacks like the GC icon in DrRacket will be reliably
invoked for major collections.
9222a135c3