The attached script creates a threading.local within a QThread, and
stores a value in it. It then reads this value back immediately, and
later from an event handler.
Unexpectedly, by the time we get to the event handler, the contents of
the threading.local has been destroyed.
I suspect there are infelicitious interactions between QThread,
thread._local, and the garbage collector. I haven't looked closely;
it's easier to work around the problem. It's possible this is a python
bug in the handling of alien threads.
Tripped over this one because it breaks sqlalchemy's scoped_session
import sys
from PyQt4.QtCore import *
from PyQt4 import QtGui
import threading
class Blob(object):
def __del__(self):
print "Deleted!"
class Worker(QObject):
@pyqtSlot()
def start(self):
self.local = threading.local()
self.local.value = Blob()
self.timer = QTimer()
self.timer.setInterval(1000)
self.timer.timeout.connect(self.timeout)
self.timer.setSingleShot(True)
self.timer.start()
print getattr(self.local, 'value', None)
def timeout(self):
print getattr(self.local, 'value', None)
class Caller(QObject):
start = pyqtSignal()
app = QtGui.QApplication(sys.argv)
thread = QThread()
worker = Worker()
worker.moveToThread(thread)
thread.start()
caller = Caller()
caller.start.connect(worker.start)
caller.start.emit()
sys.exit(app.exec_())
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