How to test concurrency using py.test

Question

I want to test a thread safety of a function using py.test My efforts:

def function_to_be_tested(arg1,arg2):
   some functionality

class Test:
   def setup()
   def teardown()
   def test_conc()
       p1=Process(taget=function_to_be_tested,args(arg1,arg2,))
       p2=Process (taget=function_to_be_tested,args(arg1,arg3,))
       p1.start()
       p2.start()
       p1.join()
       p2.join()

excute above file using py.test commad. This shows following error.

ExceptionPexpect: isalive() encountered condition where "terminated" is 0, but there was no child process. Did someone else call waitpid() on our process?

Can you help me to decode this error and also give a guidance on how to do this.

Thanks Here is the actual code I am trying and stacktrace:

import pytest
from multiprocessing import Process
from pexpect import pxssh

def func(cls,b):
    cls.s.sendline("bteq")
    cls.s.prompt()
    print b
    #some operations inside the bteq session

class Test:
    @classmethod
    def setup_class(cls):
        cls.s=pxssh.pxssh()
        cls.s.login("IP",'Username','Pwd')
    @classmethod
    def teardown_class(cls):
        cls.s.logout()
        print "teardown"

    def test_1(cls):
        p1=Process(target=func,args=(cls,13,))
        p2=Process(target=func,args=(cls,46,))
        p1.start()
        p2.start()
        p1.join()
        p2.join()

stack trace:

dipakw@dipakw-Inspiron-3558:~$ py.test -v -s test.py 
============================= test session starts ==============================
platform linux2 -- Python 2.7.6, pytest-3.0.6, py-1.4.32, pluggy-0.4.0 -- /usr/bin/python
cachedir: .cache
rootdir: /home/dipakw, inifile: 
plugins: xdist-1.15.0
collected 1 items 

test.py::Test::test_1 Process Process-1:
Traceback (most recent call last):
  File "/usr/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/usr/lib/python2.7/multiprocessing/process.py", line 114, in run
    self._target(*self._args, **self._kwargs)
  File "/home/dipakw/test.py", line 7, in func
    cls.s.prompt()
  File "/usr/lib/python2.7/dist-packages/pexpect/pxssh.py", line 352, in prompt
Process Process-2:
Traceback (most recent call last):
  File "/usr/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/usr/lib/python2.7/multiprocessing/process.py", line 114, in run
    self._target(*self._args, **self._kwargs)
  File "/home/dipakw/test.py", line 7, in func
    cls.s.prompt()
  File "/usr/lib/python2.7/dist-packages/pexpect/pxssh.py", line 352, in prompt
    i = self.expect([self.PROMPT, TIMEOUT], timeout=timeout)
    i = self.expect([self.PROMPT, TIMEOUT], timeout=timeout)
  File "/usr/lib/python2.7/dist-packages/pexpect/__init__.py", line 1418, in expect
  File "/usr/lib/python2.7/dist-packages/pexpect/__init__.py", line 1418, in expect
    timeout, searchwindowsize)
    timeout, searchwindowsize)
  File "/usr/lib/python2.7/dist-packages/pexpect/__init__.py", line 1433, in expect_list
  File "/usr/lib/python2.7/dist-packages/pexpect/__init__.py", line 1433, in expect_list
    timeout, searchwindowsize)
  File "/usr/lib/python2.7/dist-packages/pexpect/__init__.py", line 1502, in expect_loop
    timeout, searchwindowsize)
    c = self.read_nonblocking(self.maxread, timeout)
  File "/usr/lib/python2.7/dist-packages/pexpect/__init__.py", line 1502, in expect_loop
  File "/usr/lib/python2.7/dist-packages/pexpect/__init__.py", line 886, in read_nonblocking
    if not self.isalive():
    c = self.read_nonblocking(self.maxread, timeout)
  File "/usr/lib/python2.7/dist-packages/pexpect/__init__.py", line 1220, in isalive
    'on our process?')
  File "/usr/lib/python2.7/dist-packages/pexpect/__init__.py", line 886, in read_nonblocking
    if not self.isalive():
  File "/usr/lib/python2.7/dist-packages/pexpect/__init__.py", line 1220, in isalive
ExceptionPexpect: isalive() encountered condition where "terminated" is 0, but there was no child process. Did someone else call waitpid() on our process?
    'on our process?')
ExceptionPexpect: isalive() encountered condition where "terminated" is 0, but there was no child process. Did someone else call waitpid() on our process?

Nimble

Show full Traceback – Cookson

Answer 1

Try something along the lines of the below for testing concurrency / threads:

import threading
from functools import partial


@pytest.mark.django_db
def test_is_concurrency_safe():        
    # setup anything for the test...

    # recreate multiple threads calling the same function at the same time
   _call_concurrently(
        partial(my_function, args),
        partial(my_function, args),
    )

    # Test that the race condition didn't create duplicates, etc

def _call_concurrently(*callables):
    threads = [threading.Thread(target=callable_) for callable_ in callables]

    for thread in threads:
        thread.start()
    for thread in threads:
        thread.join()

Hornstein