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expander: avoid keeping thread in registry lock

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Weakly retain the lock holder in a namespace registry. Otherwise, it
can retain a thread that should have been unreachable.
This commit is contained in:
Matthew Flatt 2020-02-01 07:14:49 -07:00
parent 519e4aa9a3
commit eeb73a6c05
1 changed files with 4 additions and 4 deletions
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8
racket/src/expander/namespace/registry.rkt
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@ -16,9 +16,9 @@
(define v (unbox lock-box))
(cond
[(or (not v)
(sync/timeout 0 (car v) (cdr v)))
(sync/timeout 0 (car v) (or (weak-box-value (cdr v) never-evt))))
(define sema (make-semaphore))
(define lock (cons (semaphore-peek-evt sema) (current-thread)))
(define lock (cons (semaphore-peek-evt sema) (make-weak-box (current-thread))))
((dynamic-wind
void
(lambda ()
@ -31,10 +31,10 @@
(lambda () (loop))]))
(lambda ()
(semaphore-post sema))))]
[(eq? (current-thread) (cdr v))
[(eq? (current-thread) (weak-box-value (cdr v)))
;; This thread already holds the lock
(proc)]
[else
; Wait and try again:
(sync (car v) (cdr v))
(sync (car v) (or (weak-box-value (cdr v)) never-evt))
(loop)])))