cs: fix interaction of places and 'GC log receivers

Related to #3174

pkgs/racket-test/tests/racket/place-gc-logger.rkt

@@ -0,0 +1,25 @@
+#lang racket/base
+(require racket/place)
+
+(define (churn n)
+  (let loop ([l (cons "" 0)])
+    (if (equal? (cdr l) n)
+        (string-length (car l))
+        (loop (cons (make-string 512 #\x)
+                    (add1 (cdr l)))))))
+
+(define (go)
+  (place pch
+         (churn 100000)))
+
+(module+ main
+  (go)
+  (define receiver
+    (make-log-receiver (current-logger) 'debug 'GC))
+  (void
+   (thread
+    (lambda ()
+      (let loop ()
+        (sync receiver)
+        (loop)))))
+  (churn 100000))

racket/src/thread/pre-poll.rkt

@@ -1,20 +1,24 @@
 #lang racket/base
 (require "atomic.rkt"
-         "host.rkt")
+         "host.rkt"
+         "place-object.rkt")
 
 (provide unsafe-add-pre-poll-callback!
          call-pre-poll-external-callbacks)
 
+;; Callbacks for the original place only:
 (define pre-poll-callbacks null)
 
-;; called in atomic mode in an arbitrary host thread, but
+;; Called in atomic mode in an arbitrary host thread, but
 ;; with all other host threads paused; the given procedure
-;; will be called in atomic mode, possibly in the schduler
+;; will be called in atomic mode, possibly in the schduler,
+;; in the original place
 (define (unsafe-add-pre-poll-callback! proc)
   (set! pre-poll-callbacks (cons proc pre-poll-callbacks)))
 
 ;; in atomic mode
 (define (call-pre-poll-external-callbacks)
+  (when (eq? current-place initial-place)
     (unless (null? pre-poll-callbacks)
       ;; disable interrupts to avoid a case with `unsafe-add-pre-poll-callback!`
       (host:disable-interrupts)
@@ -23,4 +27,4 @@
       (host:enable-interrupts)
       ;; Call the callbacks
       (for ([cb (in-list (reverse l))])
-      (cb))))
+        (cb)))))