[ clisp-Bugs-3545905 ] Hang with exemption

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Bugs item #3545905, was opened at 2012-07-19 08:29
Message generated for change (Comment added) made by vtz
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Category: multithreading
Group: lisp error
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: lmj ()
Assigned to: Vladimir Tzankov (vtz)
Summary: Hang with exemption

Initial Comment:
The following RUN function eventually hangs for both the latest build (15589) and clisp-2.49.

(defstruct sema
  (count 0)
  (lock (mt:make-mutex))
  (cvar (mt:make-exemption)))

(defun inc-sema (sema)
  (mt:with-mutex-lock ((sema-lock sema))
    (incf (sema-count sema))
    (mt:exemption-signal (sema-cvar sema))))

(defun dec-sema (sema)
  (mt:with-mutex-lock ((sema-lock sema))
    (loop (cond ((plusp (sema-count sema))
                 (decf (sema-count sema))
                 (return))
                (t
                 (mt:exemption-wait
                  (sema-cvar sema) (sema-lock sema)))))))

(defun test (thread-count)
  (let ((from-threads (make-sema)))
    (loop repeat thread-count do
         (mt:make-thread
          (lambda () (inc-sema from-threads))
          :name "test"))
    (loop repeat thread-count do (dec-sema from-threads))))

(defun run ()
  (loop
     (test 16)
     (format t ".")
     (finish-output)))

Sometimes the outcome with the latest build is:

Internal error: statement in file "zthread.d", line 771 has been reached!!

The number of iterations until hanging tends to decrease as thread-count increases.

The following replacement for TEST should also be checked (it has exposed bugs in other CL implementations where the previous TEST did not).

(defun test (thread-count)
  (let ((from-threads (make-sema))
        (to-threads   (make-sema)))
    (loop repeat thread-count do
         (mt:make-thread
          (lambda ()
            (dec-sema to-threads)
            (inc-sema from-threads))
          :name "test"))
    (loop repeat thread-count do (inc-sema to-threads))
    (loop repeat thread-count do (dec-sema from-threads))))

Linux xi 3.2.0-24-generic-pae #39-Ubuntu SMP Mon May 21 18:54:21 UTC 2012 i686 i686 i386 GNU/Linux

gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) 

GNU CLISP 2.49+ (2010-07-17) (built 3551638844) (memory 3551639097)
Software: GNU C 4.6.3 
gcc -g -O2 -W -Wswitch -Wcomment -Wpointer-arith -Wreturn-type -Wmissing-declarations -Wimplicit -Wno-sign-compare -Wno-format-nonliteral -O2 -fexpensive-optimizations -falign-functions=4 -pthread -DENABLE_UNICODE -DMULTITHREAD -DPOSIX_THREADS -DDYNAMIC_MODULES  libgnu.a  -lreadline -lncurses -ldl   -lsigsegv  
SAFETY=0 HEAPCODES LINUX_NOEXEC_HEAPCODES GENERATIONAL_GC SPVW_BLOCKS SPVW_MIXED TRIVIALMAP_MEMORY
libsigsegv 2.9
libreadline 6.2
Features: 
(REGEXP WILDCARD SYSCALLS I18N LOOP COMPILER CLOS MOP CLISP ANSI-CL COMMON-LISP LISP=CL
 INTERPRETER LOGICAL-PATHNAMES MT SOCKETS GENERIC-STREAMS SCREEN GETTEXT UNICODE
 BASE-CHAR=CHARACTER PC386 UNIX)
C Modules: (clisp i18n syscalls regexp)
Installation directory: /home/jlawrence/usr/stow/clisp-dev/lib/clisp-2.49+/
User language: ENGLISH
Machine: I686 (I686) xi [127.0.1.1]

----------------------------------------------------------------------

>Comment By: Vladimir Tzankov (vtz)
Date: 2012-07-20 00:27

Message:
I can't reproduce it (tested both on Linux and OSX).
I used up to 128 threads and waited about 5 minutes on each run. Also
tested the second 'test' function without experiencing problems. 

Reaching zthread.d:771 means inconsistency in internal mutex record.
Will continue to test - any additional info (though not sure what to ask
for - debugging is an option but it's not easy one) will be helpful.


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