Eventspaces and Threads

When a new eventspace is created, a corresponding handler thread is created for the eventspace. When the system dispatches an event for an eventspace, it always does so in the eventspace's handler thread. A handler procedure can create new threads that run indefinitely, but as long as the handler thread is running a handler procedure, no new events can be dispatched for the corresponding eventspace.

When a handler thread shows a dialog, the dialog's show method implicitly calls yield for as long as the dialog is shown. When a non-handler thread shows a dialog, the non-handler thread simply blocks until the dialog is dismissed. Calling yield with no arguments from a non-handler thread has no effect. Calling yield with a semaphore from a non-handler thread is equivalent to calling MzScheme's semaphore-wait.