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Background Jobs.ipynb
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Simple interactive bacgkround jobs with IPython

We start by loading the backgroundjobs library and defining a few trivial functions to illustrate things with.

In [1]:
from IPython.lib import backgroundjobs as bg

import sys
import time

def sleepfunc(interval=2, *a, **kw):
    args = dict(interval=interval,
                args=a,
                kwargs=kw)
    time.sleep(interval)
    return args

def diefunc(interval=2, *a, **kw):
    time.sleep(interval)
    raise Exception("Dead job with interval %s" % interval)

def printfunc(interval=1, reps=5):
    for n in range(reps):
        time.sleep(interval)
        print 'In the background...', n
        sys.stdout.flush()
    print 'All done!'
    sys.stdout.flush()

Now, we can create a job manager (called simply jobs) and use it to submit new jobs.

Run the cell below, it will show when the jobs start. Wait a few seconds until you see the 'all done' completion message:

In [10]:
jobs = bg.BackgroundJobManager()

# Start a few jobs, the first one will have ID # 0
jobs.new(sleepfunc, 4)
jobs.new(sleepfunc, kw={'reps':2})
jobs.new('printfunc(1,3)')

Starting job # 0 in a separate thread.
Starting job # 2 in a separate thread.
Starting job # 3 in a separate thread.
Out[10]:
<BackgroundJob #3: printfunc(1,3)>
In the background... 0

In the background... 1

In the background... 2

All done!

You can check the status of your jobs at any time:

In [11]:
jobs.status()

Completed jobs:
0 : <function sleepfunc at 0x314f848>
2 : <function sleepfunc at 0x314f848>
3 : printfunc(1,3)

For any completed job, you can get its result easily:

In [12]:
jobs[0].result
Out[12]:
{'args': (), 'interval': 4, 'kwargs': {}}

Errors and tracebacks

The jobs manager tries to help you with debugging:

In [13]:
# This makes a couple of jobs which will die.  Let's keep a reference to
# them for easier traceback reporting later
diejob1 = jobs.new(diefunc, 1)
diejob2 = jobs.new(diefunc, 2)

Starting job # 4 in a separate thread.
Starting job # 5 in a separate thread.

You can get the traceback of any dead job. Run the line below again interactively until it prints a traceback (check the status of the job):

In [14]:
print "Status of diejob1:", diejob1.status
diejob1.traceback()  # jobs.traceback(4) would also work here, with the job number

Status of diejob1: Dead (Exception), call jobs.traceback() for details
---------------------------------------------------------------------------
Exception                                 Traceback (most recent call last)
/home/fperez/usr/opt/virtualenv/ipython-0.13.2/lib/python2.7/site-packages/IPython/lib/backgroundjobs.pyc in call(self)
    482 
    483     def call(self):
--> 484         return self.func(*self.args, **self.kwargs)

<ipython-input-1-fbbbd0d2a1c3> in diefunc(interval, *a, **kw)
     13 def diefunc(interval=2, *a, **kw):
     14     time.sleep(interval)
---> 15     raise Exception("Dead job with interval %s" % interval)
     16 
     17 def printfunc(interval=1, reps=5):

Exception: Dead job with interval 1

This will print all tracebacks for all dead jobs:

In [15]:
jobs.traceback()

Traceback for: <BackgroundJob #4: <function diefunc at 0x314f668>>
---------------------------------------------------------------------------
Exception                                 Traceback (most recent call last)
/home/fperez/usr/opt/virtualenv/ipython-0.13.2/lib/python2.7/site-packages/IPython/lib/backgroundjobs.pyc in call(self)
    482 
    483     def call(self):
--> 484         return self.func(*self.args, **self.kwargs)

<ipython-input-1-fbbbd0d2a1c3> in diefunc(interval, *a, **kw)
     13 def diefunc(interval=2, *a, **kw):
     14     time.sleep(interval)
---> 15     raise Exception("Dead job with interval %s" % interval)
     16 
     17 def printfunc(interval=1, reps=5):

Exception: Dead job with interval 1

Traceback for: <BackgroundJob #5: <function diefunc at 0x314f668>>
---------------------------------------------------------------------------
Exception                                 Traceback (most recent call last)
/home/fperez/usr/opt/virtualenv/ipython-0.13.2/lib/python2.7/site-packages/IPython/lib/backgroundjobs.pyc in call(self)
    482 
    483     def call(self):
--> 484         return self.func(*self.args, **self.kwargs)

<ipython-input-1-fbbbd0d2a1c3> in diefunc(interval, *a, **kw)
     13 def diefunc(interval=2, *a, **kw):
     14     time.sleep(interval)
---> 15     raise Exception("Dead job with interval %s" % interval)
     16 
     17 def printfunc(interval=1, reps=5):

Exception: Dead job with interval 2

The job manager can be flushed of all completed jobs at any time:

In [16]:
jobs.flush()

Flushing 3 Completed jobs.
Flushing 2 Dead jobs.

After that, the status is simply empty:

In [17]:
jobs.status()

Jobs have a .join method that lets you wait on their thread for completion:

In [18]:
j = jobs.new(sleepfunc, 2)
j.join?

Starting job # 0 in a separate thread.

Exercise

  1. Start a new job that calls sleepfunc with a 5-second wait
  2. Print a short message that indicates you are waiting (note: you'll need to flush stdout to see that print output appear).
  3. Wait on the job and then print its result.