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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... %i' % 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 [2]:
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[2]:
<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 [3]:
jobs.status()

Completed jobs:
0 : <function sleepfunc at 0x10521f2f0>
2 : <function sleepfunc at 0x10521f2f0>
3 : printfunc(1,3)

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

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

Errors and tracebacks

The jobs manager tries to help you with debugging:

In [5]:
# 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 [6]:
print("Status of diejob1: %s" % 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)
/Users/minrk/dev/ip/mine/IPython/lib/backgroundjobs.py in call(self)
    489 
    490     def call(self):
--> 491         return self.func(*self.args, **self.kwargs)

<ipython-input-1-169e49434ce0> 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 [7]:
jobs.traceback()

Traceback for: <BackgroundJob #4: <function diefunc at 0x10521f7b8>>
---------------------------------------------------------------------------
Exception                                 Traceback (most recent call last)
/Users/minrk/dev/ip/mine/IPython/lib/backgroundjobs.py in call(self)
    489 
    490     def call(self):
--> 491         return self.func(*self.args, **self.kwargs)

<ipython-input-1-169e49434ce0> 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 0x10521f7b8>>
---------------------------------------------------------------------------
Exception                                 Traceback (most recent call last)
/Users/minrk/dev/ip/mine/IPython/lib/backgroundjobs.py in call(self)
    489 
    490     def call(self):
--> 491         return self.func(*self.args, **self.kwargs)

<ipython-input-1-169e49434ce0> 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 [8]:
jobs.flush()

Flushing 3 Completed jobs.
Flushing 2 Dead jobs.

After that, the status is simply empty:

In [9]:
jobs.status()

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

In [10]:
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.