[PyKDE] pyqt/mysqld thread deadlock

Phil Thompson phil at river-bank.demon.co.uk
Wed Jan 1 20:40:04 CET 2003


On Wednesday 01 January 2003 5:58 pm, Kaleb Pederson wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Ok. I have a PyQt program using mysql as a database with mysqldb as my
> database client. I'm spawning qt threads to do all the work before I call a
> postevent to let my application know I'm done.
>
> It turns out, however, that the thread locks in the middle of my run() call
> and never completes. I'm cross-posting this message as I'm not familiar
> with Python extension modules and I don't know if PyQt could have caused
> this, it is a Python bug (or feature) or if there is a problem in the
> mysqldb module code.
>
> Here's my run call:
>
>  def run(self):
>  """ called after the thread is spawned """
>  try:
>
>  # never makes it through the quick_find_customer call....
>  self.data = quick_find.quick_find_customer(self.parameters)
>  print "quick find returned:",self.data
>
>  event = QCustomEvent(self.eventID)
>  event.setData(self.data)
>
>  QThread.postEvent(self.receiver,event)
>
>  except Exception, msg:
>  print msg
>
>
> I traced through everything and it seems to be blocking in the mysql code:
>
>  def _execute(self, query, args):
>  # makes it into the function but ...
>  from types import ListType, TupleType
>  from sys import exc_info
>  # it never makes it this far....
>  try:
>  if args is None:
>  r = self._query(query)
>
> Once it locks, I get the following backtrace (using a full debug build of
> Python/PyQt/etc.):
>
> #0 0x4019fd49 in sigsuspend () from /lib/libc.so.6
> #1 0x40033858 in __pthread_wait_for_restart_signal () from
> /lib/libpthread.so.0
> #2 0x400300eb in pthread_cond_wait () from /lib/libpthread.so.0
> #3 0x080b5c0e in PyThread_acquire_lock (lock=0x813d418, waitflag=1) at
> Python/thread_pthread.h:374
> #4 0x080a5874 in lock_import () at Python/import.c:166
> #5 0x080a81b2 in PyImport_ImportModuleEx (name=0x8182fc4 "types",
> globals=0x87f56a4, locals=0x8114484, fromlist=0x87f83f4)
>  at Python/import.c:1657
> #6 0x080f617b in builtin___import__ (self=0x0, args=0x813ab0c) at
> Python/bltinmodule.c:40
> #7 0x080f3ec6 in PyCFunction_Call (func=0x81379f0, arg=0x813ab0c, kw=0x0)
> at Objects/methodobject.c:79
> #8 0x080cdd9b in PyObject_Call (func=0x81379f0, arg=0x813ab0c, kw=0x0) at
> Objects/abstract.c:1688
> #9 0x0808ea7b in PyEval_CallObjectWithKeywords (func=0x81379f0,
> arg=0x813ab0c, kw=0x0) at Python/ceval.c:3058
> #10 0x0808a3f8 in eval_frame (f=0x852f99c) at Python/ceval.c:1843
>
> <snip>
>
> #32 0x0808d204 in PyEval_EvalCodeEx (co=0x870c6b0, globals=0x871a6cc,
> locals=0x0, args=0x81e2d78, argcount=1, kws=0x0, kwcount=0,
>  defs=0x0, defcount=0, closure=0x0) at Python/ceval.c:2595
> #33 0x080e30df in function_call (func=0x870f34c, arg=0x81e2d64, kw=0x0) at
> Objects/funcobject.c:374
> #34 0x080cdd9b in PyObject_Call (func=0x870f34c, arg=0x81e2d64, kw=0x0) at
> Objects/abstract.c:1688
> #35 0x080d6f80 in instancemethod_call (func=0x870f34c, arg=0x81e2d64,
> kw=0x0) at Objects/classobject.c:2292
> #36 0x080cdd9b in PyObject_Call (func=0x8582af4, arg=0x81e2d64, kw=0x0) at
> Objects/abstract.c:1688
> #37 0x0808ea7b in PyEval_CallObjectWithKeywords (func=0x8582af4,
> arg=0x81e2d64, kw=0x0) at Python/ceval.c:3058
> #38 0x40023ecb in sipEvalMethod (pm=0x8734788, args=0x81e2d64) at
> siplib.c:2898
> #39 0x414a85a4 in sipQThread::sipVH_run(sipMethodCache const*,
> _sipThisType*) ()
>  from /usr/local/lib/python2.2/site-packages/libqtcmodule.so
> #40 0x414a8553 in sipQThread::run() () from
> /usr/local/lib/python2.2/site-packages/libqtcmodule.so
> #41 0x40517726 in QThreadPrivate::start(QThread*) (thread=0x8734778) at
> kernel/qthread_unix.cpp:79
> - ---Type <return> to continue, or q <return> to quit---
> #42 0x4051675b in start_thread (_arg=0x87327a0) at
> kernel/qthread_unix.cpp:98 #43 0x40031160 in pthread_start_thread () from
> /lib/libpthread.so.0 #44 0x40031262 in pthread_start_thread_event () from
> /lib/libpthread.so.0
>
> So does anyone have any idea what's wrong or how to fix it? Please email me
> as well if you aren't posting to the PyQt/Python list (kibab at icehouse
> dot net).

To quote the Python source the lock is "to prevent parallel imports of the 
same module in different threads to return with a partially loaded module". 
What other imports (or the same import in other threads) might be happening 
at the same time?

Phil





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