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Issue with breakpoints in multithreading

Aperta
  • Qualcosa non va?
#14 1 commento 1 reazione 0 assegnatari Vedi su GitHub

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Valutazione

Difficoltà
4/5
Tempo stimato
3-5 giorni
Idoneità per principianti
35/100
Tipo di issue
Bug
Chiarezza
Abbastanza chiara
Stato di attività
Ferma
Stack tecnologico
python
Ambito
devtools

Direzione di ricerca

Start with the parallel_fibonacci.py reproduction and the trepan3k entry point; set breakpoints on lines 10 and 29, then compare the behavior with pydb --threading. Trace how trepan3k handles threads and breakpoint dispatch, and consider the issue done when breakpoints inside fibonacci_task and queue_task stop execution as shown in the report.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

Hi,
It seems trepan3k is not able to stop in breakpoints put inside a function launched as a thread target.
For example, for the script:

import threading
from queue import Queue

fibo_dict = {}
input_list = [3,5,7,9]
shared_queue = Queue()
queue_condition = threading.Condition()

def fibonacci_task(condition):
      with condition: # line 10

        while shared_queue.empty():
            print("[{}] - waiting for elements in queue..".format(threading.current_thread().name))
            condition.wait()

        else:
            value = shared_queue.get()
            a, b = 0, 1
            for item in range(value):
                a, b = b, a + b
                fibo_dict[value] = a

        shared_queue.task_done()
        print("[{}] fibonacci of key [{}] with result [{}]".
              format(threading.current_thread().name, value, fibo_dict[value]))

def queue_task(condition):
    print('Starting queue_task...') # line 29
    with condition:
        for item in input_list:
            shared_queue.put(item)

        print("Notifying fibonacci task threads that the queue is ready to consume...")
        condition.notifyAll()

def main():
    threads = []
    for i in range(3):
        thread = threading.Thread(target=fibonacci_task, args=(queue_condition,))
        thread.daemon = False
        threads.append(thread)

    [thread.start() for thread in threads]

    prod = threading.Thread(name='queue_task_thread', target=queue_task, args=(queue_condition,))
    prod.daemon = False
    prod.start()

    [thread.join() for thread in threads]

    print("[{}] - Result {}".format(threading.current_thread().name, fibo_dict))

if __name__=='__main__':
    main()

If we put breakpoints inside fibonacci_task or queue_task functions:
Trepan3k Execution flow:

$ trepan3k parallel_fibonacci.py
(/tmp/python-debug/trepan3k_issue/parallel_fibonacci.py:1): <module>
-> 1 import threading
(trepan3k) break 10
Breakpoint 1 set at line 10 of file /tmp/python-debug/trepan3k_issue/parallel_fibonacci.py
(trepan3k) break 29
Breakpoint 2 set at line 29 of file /tmp/python-debug/trepan3k_issue/parallel_fibonacci.py
(trepan3k) continue
[Thread-1] - waiting for elements in queue..
[Thread-2] - waiting for elements in queue..
[Thread-3] - waiting for elements in queue..
Starting queue_task...
Notifying fibonacci task threads that the queue is ready to consume...
[Thread-3] fibonacci of key [3] with result [2]
[Thread-2] fibonacci of key [5] with result [5]
[Thread-1] fibonacci of key [7] with result [13]
[MainThread] - Result {3: 2, 5: 5, 7: 13}
The program finished - quit or restart
(/tmp/python-debug/trepan3k_issue/parallel_fibonacci.py:56 @131): <module>
-> 56     main()

The debug session ends without stopping in the breakpoints.

If we launch the same debug sessoin with pydb:
Pydb Execution flow:

$ pydb --threading parallel_fibonacci.py 
--Call level -1 
Current thread is MainThread
(/tmp/python-debug/trepan3k_issue/parallel_fibonacci.py:1):  <module>
1 import threading
(Pydb) break 10
Breakpoint 1 set in file /tmp/python-debug/trepan3k_issue/parallel_fibonacci.py, line 10.
(Pydb) break 29
Breakpoint 2 set in file /tmp/python-debug/trepan3k_issue/parallel_fibonacci.py, line 29.
(Pydb) continue
Current thread is Thread-1
(/tmp/python-debug/trepan3k_issue/parallel_fibonacci.py:10):  fibonacci_task
10     with condition:
(Pydb) continue
Current thread is Thread-2
(/tmp/python-debug/trepan3k_issue/parallel_fibonacci.py:10):  fibonacci_task
10     with condition:
(Pydb) continue
[Thread-1] - waiting for elements in queue..
Current thread is Thread-3
(/tmp/python-debug/trepan3k_issue/parallel_fibonacci.py:10):  fibonacci_task
10     with condition:
(Pydb) continue
Current thread is queue_task_thread
(/tmp/python-debug/trepan3k_issue/parallel_fibonacci.py:29):  queue_task
29     print('Starting queue_task...')
(Pydb) [Thread-2] - waiting for elements in queue..

Hope this is useful
Regards

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Python
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