Summary

mutex-lock! doesn't always lock mutex

Metadata

• Id: 9a2dce58f392bf05999065d63e36f1e318663bfe
• Trac id: 1696
• Type: defect
• Reporter: megane
• Owner:
• Cc:
• Status: new
• Component: unknown
• Estimated difficulty: insane
• Resolution:
• Priority: major
• Milestone: someday
• Version: 5.2.0
• Changetime: 2020-04-18 14:30:06 UTC
• Created: 2020-04-18 14:24:09 UTC
• Keywords: srfi-69 mutex race threads scheduler

Description

 ;; From C4 tests/mutex-test.scm
 (import scheme)
 (cond-expand
  (chicken-5 (import (chicken base)
 		    (chicken type)
 		    (chicken format)
 		    srfi-18))
  (else (import chicken) (use srfi-18)))
 
 (define-record-printer (mutex x out)
   (format out "<mutex ~a ~a~a ~a (owner ~a) waiting ~a>"
 	  (mutex-name x)
 	  (if (##sys#slot x 5) "LOCKED" "FREE")
 	  (if (##sys#slot x 4) "/ABANDONED" "")
 	  (mutex-state x)
 	  (if (##sys#slot x 2) (##sys#slot x 2) "none")
 	  (##sys#slot x 3)
 	  ))
 
 (let ((m1 (make-mutex)))
   ;; (print m1)
   (mutex-lock! m1)
   (print m1)
   (print* "l")
   ;; (thread-sleep! 0.001)
   (let ((t1 (thread-start! (lambda ()
 			     (print* "t")
 			     (mutex-lock! m1 0.001)
 			     (print "\noh no, we got the mutex")
 			     (print m1)
 			     (exit 1)))))
     (print* "y")
     (thread-yield!)
     (print* "Y")
     (when (eq? 'ready (##sys#slot t1 3)) ;; <- #3 thread state
       (print* "X")
       (thread-sleep! 1)
       (print* "Z"))))
 
 (print* ".")
 
 ;; OK run:
 ;; lytY.<mutex mutex0 LOCKED #<thread: primordial> (owner #<thread: primordial>) waiting ()>
 
 ;; Failing run:
 ;; lytYX
 ;; oh no, we got the mutex
 ;; <mutex mutex0 LOCKED #<thread: primordial> (owner #<thread: primordial>) waiting ()>

Changes and comments

[2020-04-18 14:30:06 UTC] megane wrote:

Fails when compiled and in interpreter. It has taken up to 1250 tries for this to fail, which is less than a minute.