I am using code as below for multiple thread in python3, I tried Threads in cpu_count() with 2, 3 and 4 times, but I am not sure if all those threads in using, how can I check if there are some queues are never used?
queue = Queue()
for x in range(cpu_count() * 2):
worker = DownloadWorker(queue)
worker.daemon = True
worker.start()
queue.join()
class DownloadWorker(Thread):
def __init__(self, queue):
Thread.__init__(self)
self.queue = queue
def run(self):
while True:
link, download_path = self.queue.get()
download_link(link, download_path)
self.queue.task_done()
def downloadImage(imageServer, imageLocal, queue):
queue.put((imageServer, imageLocal))
if you want to know if all your threads are working, you can just print the thread name every time it starts a task:
from threading import Thread
from queue import Queue
import random
import time
class DownloadWorker(Thread):
def __init__(self, queue):
Thread.__init__(self)
self.queue = queue
def run(self):
while True:
self.queue.get()
print('Thread: {}'.format(self.name))
time.sleep(random.random())
queue = Queue()
for i in range(100):
queue.put('data')
queue.task_done()
for x in range(4):
worker = DownloadWorker(queue)
worker.daemon = True
worker.start()
time.sleep(10)
Queue uses threading.Condition internally to block/release threads that called get() and threading.Condition uses a threading.Lock. From the documentation of threading.Lock:
When more than one thread is blocked in acquire() waiting for the
state to turn to unlocked, only one thread proceeds when a release()
call resets the state to unlocked; which one of the waiting threads
proceeds is not defined, and may vary across implementations.
I hope this answers the question.
Related
Im trying to generate data in two threads and get that data in a separate thread that prints the data.
3 threads, 2 threads generate data , 1 thread consumes the data generated.
The Problem: not getting both generated data into the consumer thread
How can I pass data generated in 2 threads and deliver it in the consumer thread?
#from threading import Thread
import concurrent.futures
import time
# A thread that produces data
def producer(out_q):
while True:
# Produce some data
global data
data = data + 2
out_q.put(data)
# Another thread that produces data
def ac(out2_q):
while True:
global x
x = x + 898934567
out2_q.put(data)
# A thread that consumes data
def consumer(in_q):
while True:
# Get BOTH produced data from 2 threads
data = in_q.get()
# Process the data
time.sleep(.4)
print(data, end=' ', flush=True)
x=0
data = 0
q = Queue()
with concurrent.futures.ThreadPoolExecutor() as executor:
t1 = executor.submit(consumer, q)
t2 = executor.submit(producer,q)
t3 = executor.submit(ac, q)```
I recommend to go with threading.Thread in this case. Please see the code below and follow comments. Feel free to ask questions.
from threading import Thread, Event
from queue import Queue
import time
def producer_one(q: Queue, e: Event):
while not e.is_set():
q.put("one")
time.sleep(1)
print("Producer # one stopped")
def producer_two(q: Queue, e: Event):
while not e.is_set():
q.put("two")
time.sleep(2)
print("Producer # two stopped")
def consumer(q: Queue):
while True:
item = q.get()
print(item)
q.task_done() # is used to unblock queue - all tasks were done
time.sleep(2)
# will never be printed ! - since it is daemon thread
print("All work is done by consumer!")
if __name__ == '__main__':
_q = Queue() # "connects" threads
_e = Event() # is used to stop producers from the Main Thread
# create threads block
producer_th1 = Thread(target=producer_one, args=(_q, _e, ))
producer_th2 = Thread(target=producer_two, args=(_q, _e, ))
# daemon means that thread will be stopped when main thread stops
consumer_th = Thread(target=consumer, args=(_q, ), daemon=True)
try:
# starts block:
producer_th1.start()
producer_th2.start()
consumer_th.start()
time.sleep(20)
_e.set() # ask producers to stop
except KeyboardInterrupt:
_e.set() # ask producer threads to stop
print("Asked Producer Threads to stop")
finally:
producer_th1.join() # main thread is block until producer_th1 is not stopped
producer_th2.join() # main thread is block until producer_th2 is not stopped
_q.join() # now wait consumer to finish all tasks from queue
print("Queue is empty and program will be finished soon")
time.sleep(2) # just wait 2 seconds to show that consumer stops with main thread
print("All done!")
I am trying to figure out why this code crashes if I try to run the threads for a second time once they are completed.
The first time I click "Start 5 Threads" It runs just fine and finishes. But if I click it again. The entire program crashes and I get the QThread: Destroyed while thread is still running Error
This code was found on the web. I am trying to learn from it.
import time
import sys
from PyQt5.QtCore import QObject, QThread, pyqtSignal, pyqtSlot
from PyQt5.QtWidgets import QApplication, QPushButton, QTextEdit, QVBoxLayout, QWidget
def trap_exc_during_debug(*args):
# when app raises uncaught exception, print info
print(args)
# install exception hook: without this, uncaught exception would cause application to exit
sys.excepthook = trap_exc_during_debug
class Worker(QObject):
"""
Must derive from QObject in order to emit signals, connect slots to other signals, and operate in a QThread.
"""
sig_step = pyqtSignal(int, str) # worker id, step description: emitted every step through work() loop
sig_done = pyqtSignal(int) # worker id: emitted at end of work()
sig_msg = pyqtSignal(str) # message to be shown to user
def __init__(self, id: int):
super().__init__()
self.__id = id
self.__abort = False
#pyqtSlot()
def work(self):
"""
Pretend this worker method does work that takes a long time. During this time, the thread's
event loop is blocked, except if the application's processEvents() is called: this gives every
thread (incl. main) a chance to process events, which in this sample means processing signals
received from GUI (such as abort).
"""
thread_name = QThread.currentThread().objectName()
thread_id = int(QThread.currentThreadId()) # cast to int() is necessary
self.sig_msg.emit('Running worker #{} from thread "{}" (#{})'.format(self.__id, thread_name, thread_id))
for step in range(100):
time.sleep(0.1)
self.sig_step.emit(self.__id, 'step ' + str(step))
# check if we need to abort the loop; need to process events to receive signals;
app.processEvents() # this could cause change to self.__abort
if self.__abort:
# note that "step" value will not necessarily be same for every thread
self.sig_msg.emit('Worker #{} aborting work at step {}'.format(self.__id, step))
break
self.sig_done.emit(self.__id)
def abort(self):
self.sig_msg.emit('Worker #{} notified to abort'.format(self.__id))
self.__abort = True
class MyWidget(QWidget):
NUM_THREADS = 5
# sig_start = pyqtSignal() # needed only due to PyCharm debugger bug (!)
sig_abort_workers = pyqtSignal()
def __init__(self):
super().__init__()
self.setWindowTitle("Thread Example")
form_layout = QVBoxLayout()
self.setLayout(form_layout)
self.resize(400, 800)
self.button_start_threads = QPushButton()
self.button_start_threads.clicked.connect(self.start_threads)
self.button_start_threads.setText("Start {} threads".format(self.NUM_THREADS))
form_layout.addWidget(self.button_start_threads)
self.button_stop_threads = QPushButton()
self.button_stop_threads.clicked.connect(self.abort_workers)
self.button_stop_threads.setText("Stop threads")
self.button_stop_threads.setDisabled(True)
form_layout.addWidget(self.button_stop_threads)
self.log = QTextEdit()
form_layout.addWidget(self.log)
self.progress = QTextEdit()
form_layout.addWidget(self.progress)
QThread.currentThread().setObjectName('main') # threads can be named, useful for log output
self.__workers_done = None
self.__threads = None
def start_threads(self):
self.log.append('starting {} threads'.format(self.NUM_THREADS))
self.button_start_threads.setDisabled(True)
self.button_stop_threads.setEnabled(True)
self.__workers_done = 0
self.__threads = []
for idx in range(self.NUM_THREADS):
worker = Worker(idx)
thread = QThread()
thread.setObjectName('thread_' + str(idx))
self.__threads.append((thread, worker)) # need to store worker too otherwise will be gc'd
worker.moveToThread(thread)
# get progress messages from worker:
worker.sig_step.connect(self.on_worker_step)
worker.sig_done.connect(self.on_worker_done)
worker.sig_msg.connect(self.log.append)
# control worker:
self.sig_abort_workers.connect(worker.abort)
# get read to start worker:
# self.sig_start.connect(worker.work) # needed due to PyCharm debugger bug (!); comment out next line
thread.started.connect(worker.work)
thread.start() # this will emit 'started' and start thread's event loop
# self.sig_start.emit() # needed due to PyCharm debugger bug (!)
#pyqtSlot(int, str)
def on_worker_step(self, worker_id: int, data: str):
self.log.append('Worker #{}: {}'.format(worker_id, data))
self.progress.append('{}: {}'.format(worker_id, data))
#pyqtSlot(int)
def on_worker_done(self, worker_id):
self.log.append('worker #{} done'.format(worker_id))
self.progress.append('-- Worker {} DONE'.format(worker_id))
self.__workers_done += 1
if self.__workers_done == self.NUM_THREADS:
self.log.append('No more workers active')
self.button_start_threads.setEnabled(True)
self.button_stop_threads.setDisabled(True)
# self.__threads = None
#pyqtSlot()
def abort_workers(self):
self.sig_abort_workers.emit()
self.log.append('Asking each worker to abort')
for thread, worker in self.__threads: # note nice unpacking by Python, avoids indexing
thread.quit() # this will quit **as soon as thread event loop unblocks**
thread.wait() # <- so you need to wait for it to *actually* quit
# even though threads have exited, there may still be messages on the main thread's
# queue (messages that threads emitted before the abort):
self.log.append('All threads exited')
if __name__ == "__main__":
app = QApplication([])
form = MyWidget()
form.show()
sys.exit(app.exec_())
The problem is solved by passing him as a parent to self. You must change:
thread = QThread()
to:
thread = QThread(parent=self)
I am trying to figure out why this code crashes if I try to run the threads for a second time once they are completed.
The first time I click "Start 5 Threads" It runs just fine and finishes. But if I click it again. The entire program crashes and I get the QThread: Destroyed while thread is still running Error
This code was found on the web. I am trying to learn from it.
import time
import sys
from PyQt5.QtCore import QObject, QThread, pyqtSignal, pyqtSlot
from PyQt5.QtWidgets import QApplication, QPushButton, QTextEdit, QVBoxLayout, QWidget
def trap_exc_during_debug(*args):
# when app raises uncaught exception, print info
print(args)
# install exception hook: without this, uncaught exception would cause application to exit
sys.excepthook = trap_exc_during_debug
class Worker(QObject):
"""
Must derive from QObject in order to emit signals, connect slots to other signals, and operate in a QThread.
"""
sig_step = pyqtSignal(int, str) # worker id, step description: emitted every step through work() loop
sig_done = pyqtSignal(int) # worker id: emitted at end of work()
sig_msg = pyqtSignal(str) # message to be shown to user
def __init__(self, id: int):
super().__init__()
self.__id = id
self.__abort = False
#pyqtSlot()
def work(self):
"""
Pretend this worker method does work that takes a long time. During this time, the thread's
event loop is blocked, except if the application's processEvents() is called: this gives every
thread (incl. main) a chance to process events, which in this sample means processing signals
received from GUI (such as abort).
"""
thread_name = QThread.currentThread().objectName()
thread_id = int(QThread.currentThreadId()) # cast to int() is necessary
self.sig_msg.emit('Running worker #{} from thread "{}" (#{})'.format(self.__id, thread_name, thread_id))
for step in range(100):
time.sleep(0.1)
self.sig_step.emit(self.__id, 'step ' + str(step))
# check if we need to abort the loop; need to process events to receive signals;
app.processEvents() # this could cause change to self.__abort
if self.__abort:
# note that "step" value will not necessarily be same for every thread
self.sig_msg.emit('Worker #{} aborting work at step {}'.format(self.__id, step))
break
self.sig_done.emit(self.__id)
def abort(self):
self.sig_msg.emit('Worker #{} notified to abort'.format(self.__id))
self.__abort = True
class MyWidget(QWidget):
NUM_THREADS = 5
# sig_start = pyqtSignal() # needed only due to PyCharm debugger bug (!)
sig_abort_workers = pyqtSignal()
def __init__(self):
super().__init__()
self.setWindowTitle("Thread Example")
form_layout = QVBoxLayout()
self.setLayout(form_layout)
self.resize(400, 800)
self.button_start_threads = QPushButton()
self.button_start_threads.clicked.connect(self.start_threads)
self.button_start_threads.setText("Start {} threads".format(self.NUM_THREADS))
form_layout.addWidget(self.button_start_threads)
self.button_stop_threads = QPushButton()
self.button_stop_threads.clicked.connect(self.abort_workers)
self.button_stop_threads.setText("Stop threads")
self.button_stop_threads.setDisabled(True)
form_layout.addWidget(self.button_stop_threads)
self.log = QTextEdit()
form_layout.addWidget(self.log)
self.progress = QTextEdit()
form_layout.addWidget(self.progress)
QThread.currentThread().setObjectName('main') # threads can be named, useful for log output
self.__workers_done = None
self.__threads = None
def start_threads(self):
self.log.append('starting {} threads'.format(self.NUM_THREADS))
self.button_start_threads.setDisabled(True)
self.button_stop_threads.setEnabled(True)
self.__workers_done = 0
self.__threads = []
for idx in range(self.NUM_THREADS):
worker = Worker(idx)
thread = QThread()
thread.setObjectName('thread_' + str(idx))
self.__threads.append((thread, worker)) # need to store worker too otherwise will be gc'd
worker.moveToThread(thread)
# get progress messages from worker:
worker.sig_step.connect(self.on_worker_step)
worker.sig_done.connect(self.on_worker_done)
worker.sig_msg.connect(self.log.append)
# control worker:
self.sig_abort_workers.connect(worker.abort)
# get read to start worker:
# self.sig_start.connect(worker.work) # needed due to PyCharm debugger bug (!); comment out next line
thread.started.connect(worker.work)
thread.start() # this will emit 'started' and start thread's event loop
# self.sig_start.emit() # needed due to PyCharm debugger bug (!)
#pyqtSlot(int, str)
def on_worker_step(self, worker_id: int, data: str):
self.log.append('Worker #{}: {}'.format(worker_id, data))
self.progress.append('{}: {}'.format(worker_id, data))
#pyqtSlot(int)
def on_worker_done(self, worker_id):
self.log.append('worker #{} done'.format(worker_id))
self.progress.append('-- Worker {} DONE'.format(worker_id))
self.__workers_done += 1
if self.__workers_done == self.NUM_THREADS:
self.log.append('No more workers active')
self.button_start_threads.setEnabled(True)
self.button_stop_threads.setDisabled(True)
# self.__threads = None
#pyqtSlot()
def abort_workers(self):
self.sig_abort_workers.emit()
self.log.append('Asking each worker to abort')
for thread, worker in self.__threads: # note nice unpacking by Python, avoids indexing
thread.quit() # this will quit **as soon as thread event loop unblocks**
thread.wait() # <- so you need to wait for it to *actually* quit
# even though threads have exited, there may still be messages on the main thread's
# queue (messages that threads emitted before the abort):
self.log.append('All threads exited')
if __name__ == "__main__":
app = QApplication([])
form = MyWidget()
form.show()
sys.exit(app.exec_())
The problem is solved by passing him as a parent to self. You must change:
thread = QThread()
to:
thread = QThread(parent=self)
I'm doing some multi-threading. I have a worker class with a work method, which I send into a separate QThread. The work method has a conditioned while loop inside. I want to be able to send a signal to the worker object to stop it (changing the _running condition to false). This will cause the while loop to exit, and a finished signal to be sent from the worker object (which is connected to the quit slot of the worker's thread).
The false condition is sent to the worker object via a signal, but it is never received, which I believe is because the while loop blocks the event-loop of its thread. Even if I put QCoreApplication.processEvents() inside the while loop, nothing happens. Where is the problem? Why isn't the signal processed? (Notice that the print statement in the stop slot on the Worker is never executed - but the weird thing is, the thread does seem to stop in a wrong way).
Here is the code:
import time, sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *
class Worker(QObject):
sgnFinished = pyqtSignal()
def __init__(self, parent):
QObject.__init__(self, parent)
self._running = True
#pyqtSlot()
def stop():
print 'stop signal received, switching while loop condition to false'
self._running = False
#pyqtSlot()
def work(self):
while self._running: #this blocks the thread, if changed to an if clause, thread finishes as expected!
QCoreApplication.processEvents() #this doesn't help!
time.sleep(0.1)
print 'doing work...'
#do some cleanup here, then signal the worker is done
self.sgnFinished.emit()
class Client(QObject):
sgnStop = pyqtSignal()
def __init__(self, parent):
QObject.__init__(self, parent)
self._thread = None
self._worker = None
def toggle(self, enable):
if enable:
if not self._thread:
self._thread = QThread()
self._worker = Worker(None)
self._worker.moveToThread(self._thread)
self._worker.sgnFinished.connect(self.on_worker_done)
self.sgnStop.connect(self._worker.stop)
self._thread.started.connect(self._worker.work)
self._thread.start()
else:
print 'sending stop signal to the worker object'
self.sgnStop.emit() #send a queuedconnection type signal to the worker, because its in another thread
#pyqtSlot()
def on_worker_done(self):
print 'workers job was interrupted manually'
self._thread.quit()
#self._thread.wait() not sure this is neccessary
if __name__ == '__main__':
app = QCoreApplication(sys.argv)
client = Client(None)
client.toggle(True)
raw_input('Press something')
client.toggle(False)
There are two main problems in your example:
Firstly, you are emitting a signal to stop the worker, but since the signal is cross-thread, it will be posted in the receiver's event-queue. However, the worker is running a blocking while-loop, so pending events cannot be processed. There are a few ways to work around this, but probably the simplest is to simply call the worker's stop method directly instead of using a signal.
Secondly, you are not explicitly running an event-loop in the main thread, so cross-thread signals sent from the worker cannot be queued. More importantly, though, there is also nothing to stop the program exiting after the user presses a key - so the client and worker will be immediately garbage-collected.
Below is a re-written version of your example which fixes all the issues:
import time, sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *
class Worker(QObject):
sgnFinished = pyqtSignal()
def __init__(self, parent):
QObject.__init__(self, parent)
self._mutex = QMutex()
self._running = True
#pyqtSlot()
def stop(self):
print 'switching while loop condition to false'
self._mutex.lock()
self._running = False
self._mutex.unlock()
def running(self):
try:
self._mutex.lock()
return self._running
finally:
self._mutex.unlock()
#pyqtSlot()
def work(self):
while self.running():
time.sleep(0.1)
print 'doing work...'
self.sgnFinished.emit()
class Client(QObject):
def __init__(self, parent):
QObject.__init__(self, parent)
self._thread = None
self._worker = None
def toggle(self, enable):
if enable:
if not self._thread:
self._thread = QThread()
self._worker = Worker(None)
self._worker.moveToThread(self._thread)
self._worker.sgnFinished.connect(self.on_worker_done)
self._thread.started.connect(self._worker.work)
self._thread.start()
else:
print 'stopping the worker object'
self._worker.stop()
#pyqtSlot()
def on_worker_done(self):
print 'workers job was interrupted manually'
self._thread.quit()
self._thread.wait()
if raw_input('\nquit application [Yn]? ') != 'n':
qApp.quit()
if __name__ == '__main__':
# prevent some harmless Qt warnings
pyqtRemoveInputHook()
app = QCoreApplication(sys.argv)
client = Client(None)
def start():
client.toggle(True)
raw_input('Press something\n')
client.toggle(False)
QTimer.singleShot(10, start)
sys.exit(app.exec_())
Cross thread signal/slot connections require a running event loop in the thread of the receiver object.
In your case there is an event loop in the second thread and it is running, but it is at all times executing your work method and never returns from there.
So all slot invocation events are stuck in the event loop's event queue.
If you want to hack around this, like you attempted with QCoreApplication.processEvents you could try getting the thread's eventDispatcher and calling its processEvent.
If you only need to end the worker, you could call the thread's requestInteruption and instead of checking for self._running you check for the thread's isInterruptionRequested.
I have created a program to generate data points of functions that I later plot. The program takes a class which defines the function, creates a data outputting object which when called generates the data to a text file. To make the whole process faster I put the jobs in threads, however when I do, the data generated is not always correct. I have attached a picture to show what I mean:
Here are some of the relevant bits of code:
from queue import Queue
import threading
import time
queueLock = threading.Lock()
workQueue = Queue(10)
def process_data(threadName, q, queue_window, done):
while not done.get():
queueLock.acquire() # check whether or not the queue is locked
if not workQueue.empty():
data = q.get()
# data is the Plot object to be run
queueLock.release()
data.parent_window = queue_window
data.process()
else:
queueLock.release()
time.sleep(1)
class WorkThread(threading.Thread):
def __init__(self, threadID, q, done):
threading.Thread.__init__(self)
self.ID = threadID
self.q = q
self.done = done
def get_qw(self, queue_window):
# gets the queue_window object
self.queue_window = queue_window
def run(self):
# this is called when thread.start() is called
print("Thread {0} started.".format(self.ID))
process_data(self.ID, self.q, self.queue_window, self.done)
print("Thread {0} finished.".format(self.ID))
class Application(Frame):
def __init__(self, etc):
self.threads = []
# does some things
def makeThreads(self):
for i in range(1, int(self.threadNum.get()) +1):
thread = WorkThread(i, workQueue, self.calcsDone)
self.threads.append(thread)
# more code which just processes the function etc, sorts out the gui stuff.
And in a separate class (as I'm using tkinter, so the actual code to get the threads to run is called in a different window) (self.parent is the Application class):
def run_jobs(self):
if self.running == False:
# threads are only initiated when jobs are to be run
self.running = True
self.parent.calcsDone.set(False)
self.parent.threads = [] # just to make sure that it is initially empty, we want new threads each time
self.parent.makeThreads()
self.threads = self.parent.threads
for thread in self.threads:
thread.get_qw(self)
thread.start()
# put the jobs in the workQueue
queueLock.acquire()
for job in self.job_queue:
workQueue.put(job)
queueLock.release()
else:
messagebox.showerror("Error", "Jobs already running")
This is all the code which relates to the threads.
I don't know why when I run the program with multiple threads some data points are incorrect, whilst running it with just 1 single thread the data is all perfect. I tried looking up "threadsafe" processes, but couldn't find anything.
Thanks in advance!