CODEWITHSUNDEEP
pythonmultithreadingbreakpointspdb
dim fish
dim fish

Reputation: 479

pdb cannot break in another thread?

Consider this multi-threaded program:

import threading

class SomeThread(threading.Thread):
  def run(self):
    a = 1
    print a

def main():
  print 'hola'
  someThread = SomeThread()
  someThread.start()

if __name__ == '__main__':
  main()

When I debug this program with pdb, at the prompt I first set a break point at each of the two print statements. Then I continue. pdb breaks at print 'hola'. I continue again and see the effect of the print in the other thread, but pdb doesn't break.

The help commands don't list anything to switch thread contexts like gdb... so... is it just not possible in one thread context to set a breakpoint that will trip in another context?

Upvotes: 25

Views: 18434

Answers (2)

Jeff Sheffield
Jeff Sheffield

Reputation: 6306

after you hit your first breakpoint, I assume you are stepping with (n) next line when you get to this line

someThread.start()

make sure you are using (s) step-into and not (n) next. pdb commands

Upvotes: -3

Matthew Trevor
Matthew Trevor

Reputation: 14952

This works for me:

import threading
import pdb

class SomeThread(threading.Thread):
  def run(self):
    a = 1
    print a
    pdb.set_trace()

def main():
  print 'hola'
  pdb.set_trace()
  someThread = SomeThread()
  someThread.start()

if __name__ == '__main__':
  main()

Which gives me:

C:\Code>python b.py
hola
> c:\code\b.py(13)main()
-> someThread = SomeThread()
(Pdb) l
  8         pdb.set_trace()
  9
 10     def main():
 11       print 'hola'
 12       pdb.set_trace()
 13  ->   someThread = SomeThread()
 14       someThread.start()
 15
 16     if __name__ == '__main__':
 17       main()
[EOF]
(Pdb) c
1
--Return--
> c:\code\b.py(8)run()->None
-> pdb.set_trace()
(Pdb) l
  3
  4     class SomeThread(threading.Thread):
  5       def run(self):
  6         a = 1
  7         print a
  8  ->     pdb.set_trace()
  9
 10     def main():
 11       print 'hola'
 12       pdb.set_trace()
 13       someThread = SomeThread()
(Pdb)

This is under Windows 7 and with Python 2.7.2. What OS & Python version are you using?

Upvotes: 9

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