Mail Archives: cygwin-developers/2001/07/10/12:17:31
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Rob,
[Moved from cygwin-patches to cygwin-developers...]
On Tue, Jul 10, 2001 at 01:24:13PM +1000, Robert Collins wrote:
> > python test.py
>
> gdb.out: the event handle is clearly wrong. Can you include the output
> of print *this ? and list (so I know what the lines actually are :])>
See attached gdb.out.
> > and the second by:
> >
> > ./python test.py
>
> Ditto for the above... but - the handle looks like it may be valid to
> me. From the bt of both outputs I suspect that it's the access mutex to
> the cond variable that is causing the grief. I'll glance at the code
> tonight.
>
> Can you give me the following as well?
> for pthread_cond::Signal
> list
> print *this
See attached gdb2.out. Unfortunately, "this" is one of those "cannot
access memory at address" addresses. I can "workaround" this problem
using the following goofy (and mostly likely invalid) procedure:
(gdb) f 5
#5 0x6105ed17 in pthread_cond::Signal (this=0xa0151a8) # <*** 1 ***
at ../../../../src/winsup/cygwin/thread.cc:443
443 if (pthread_mutex_lock (&cond_access))
Current language: auto; currently c++
(gdb) p this
$1 = (pthread_cond *) 0x200 # <*** 2 ***
(gdb) set this=0xa0151a8 # <*** 3 ***
(gdb) p this
No symbol "this" in current context.
(gdb) f 5
#5 0x6105ed17 in pthread_cond::Signal (this=0xa0151a8)
at ../../../../src/winsup/cygwin/thread.cc:443
443 if (pthread_mutex_lock (&cond_access))
(gdb) p this
$2 = (pthread_cond *) 0xa0151a8
(gdb) p *this
$3 = {<verifyable_object> = {magic = -552734646}, shared = 0, waiting = 0,
mutex = 0x0, cond_access = 0xa011108, win32_obj_id = 0x154}
Note that the value for "this" is not the same as displayed in 1 and 2
above until I reset it in 3. Any idea about what is going on?
> > I find it curious that the hang occurs in different places
> > dependent on
> > how python is invoked -- via PATH or full pathname. I'm also
> > at a lose
> > as to why sometimes I get "Cannot access memory at address
> > ..." errors.
> > Can anyone explain what is going on?
>
> If the "cannot access memory at address" error is a windows popup, it's
> an exception unhandled by cygwin for some reason. If it's in gdb, see my
> description above - it _may_ be the normal
> first-access-test-with-random-data for BadWritePointer.
The latter case is what I'm observing.
> > Is the information provided in this email useful in helping you find
> > the problem? If not, what else can I provide to assist you?
>
> Just what I've asked for. I'll have a look and see if anything obvious
> appears, otherwise it'll be back to minimising the variables.
Please let me know how I can be of further assistance.
Thanks,
Jason
--
Jason Tishler
Director, Software Engineering Phone: 732.264.8770 x235
Dot Hill Systems Corp. Fax: 732.264.8798
82 Bethany Road, Suite 7 Email: Jason DOT Tishler AT dothill DOT com
Hazlet, NJ 07730 USA WWW: http://www.dothill.com
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(gdb) bt
#0 0x77f6829b in ?? ()
#1 0x77f04f41 in ?? ()
#2 0x6105f36a in pthread_mutex::Lock (this=0xa010a58)
at ../../../../src/winsup/cygwin/thread.cc:644
#3 0x61060e26 in __pthread_mutex_lock (mutex=0xa012230)
at ../../../../src/winsup/cygwin/thread.cc:1917
#4 0x6103b3ae in pthread_mutex_lock (mutex=0xa012230)
at ../../../../src/winsup/cygwin/pthread.cc:240
#5 0x61d99e37 in PyThread_acquire_lock (lock=0xa012228, waitflag=0)
at ../Python/thread_pthread.h:298
#6 0x61d8cebd in lock_import () at ../Python/import.c:159
..
(gdb) f 2
#2 0x6105f36a in pthread_mutex::Lock (this=0xa010a58)
at ../../../../src/winsup/cygwin/thread.cc:644
644 return WaitForSingleObject (win32_obj_id, INFINITE);
Current language: auto; currently c++
(gdb) p *this
Cannot access memory at address 0x2
(gdb) list
639 }
640
641 int
642 pthread_mutex::Lock ()
643 {
644 return WaitForSingleObject (win32_obj_id, INFINITE);
645 }
646
647 int
648 pthread_mutex::TryLock ()
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(gdb) bt
#0 0x77f6829b in ?? ()
#1 0x77f04f41 in ?? ()
#2 0x6105f36a in pthread_mutex::Lock (this=0xa011108)
at ../../../../src/winsup/cygwin/thread.cc:644
#3 0x61060e26 in __pthread_mutex_lock (mutex=0xa0151b8)
at ../../../../src/winsup/cygwin/thread.cc:1917
#4 0x6103b3ae in pthread_mutex_lock (mutex=0xa0151b8)
at ../../../../src/winsup/cygwin/pthread.cc:240
#5 0x6105ed17 in pthread_cond::Signal (this=0xa0151a8)
at ../../../../src/winsup/cygwin/thread.cc:443
#6 0x61060560 in __pthread_cond_signal (cond=0xa010a5c)
at ../../../../src/winsup/cygwin/thread.cc:1628
#7 0x6103b58e in pthread_cond_signal (cond=0xa010a5c)
at ../../../../src/winsup/cygwin/pthread.cc:355
#8 0x61d9a02b in PyThread_release_lock (lock=0xa010a58)
at ../Python/thread_pthread.h:344
#9 0x61d8cf78 in unlock_import () at ../Python/import.c:179
..
(gdb) f 2
#2 0x6105f36a in pthread_mutex::Lock (this=0xa011108)
at ../../../../src/winsup/cygwin/thread.cc:644
644 return WaitForSingleObject (win32_obj_id, INFINITE);
Current language: auto; currently c++
(gdb) p *this
$1 = {<verifyable_object> = {magic = 167912352}, win32_obj_id = 0xa028ac8,
condwaits = 1, pshared = 1641717416}
(gdb) list
639 }
640
641 int
642 pthread_mutex::Lock ()
643 {
644 return WaitForSingleObject (win32_obj_id, INFINITE);
645 }
646
647 int
648 pthread_mutex::TryLock ()
(gdb) f 5
#5 0x6105ed17 in pthread_cond::Signal (this=0xa0151a8)
at ../../../../src/winsup/cygwin/thread.cc:443
443 if (pthread_mutex_lock (&cond_access))
(gdb) p *this
Cannot access memory at address 0x200
(gdb) list
438 }
439
440 void
441 pthread_cond::Signal ()
442 {
443 if (pthread_mutex_lock (&cond_access))
444 system_printf ("Failed to lock condition variable access mutex, this %0p\n", this);
445 if (!verifyable_object_isvalid (mutex, PTHREAD_MUTEX_MAGIC))
446 {
447 if (pthread_mutex_unlock (&cond_access))
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