File contents

#!/usr/bin/env python

import os, sys, math, time
import cPickle as pickle
from random import uniform

# Get task ID
task_id = int(os.environ.get('SGE_TASK_ID', '0'))

# Global parametets
cache_filename = 'scan_cache.pickle'
cache_filename_lock = 'scan_cache.pickle.lock'

# Helper functions.
def lock():
    # Wait until cache is released, then lock it!
    while True:
        if os.path.isfile(cache_filename_lock):
            time.sleep(1)
            continue
        try:
            f = open (cache_filename_lock,'w')
            f.write(str(task_id))
            f.flush()
            f.close()
            break
        except IOError, msg:
            print >> sys.stderr, str (msg)
    return
def release():
    # Release cache file lock.
    if os.path.isfile(cache_filename_lock):
        try:
            os.remove(cache_filename_lock)
        except OSError:
            pass
    return
def get_cache():
    # Read cache:
    cache = {}
    if os.path.isfile(cache_filename):
        f = open(cache_filename, 'r')
        cache = pickle.load(f)
        f.close()
    return cache
def put_cache(cache):
    f = open(cache_filename,'w')
    pickle.dump(cache, f)
    f.flush()
    f.close()
    return

# Process cache:
if task_id==0:
    from pylab import plot, show
    x_list = []
    y_list = []
    lock()
    cache = get_cache()
    release()
    for x,y in cache.values():
        x_list.append(x)
        y_list.append(y)
    plot(x_list, y_list, 'o')
    show()
else:
    # Check if the current task has result already
    lock()
    cache = get_cache()
    release()
    if cache.has_key(task_id):
        # skip calculating known results
        pass
    else:
        # calculate
        x = task_id*math.pi/100.0
        y = math.sin(x)
        time.sleep(uniform(5,25))
        # Save results
        lock()
        cache = get_cache()
        cache[task_id] = (x,y)
        put_cache(cache)
        release()

print 'Done'
#EOF