Is there an equivalent Python library for the Java FixedThreadPool?
Is there a simple ThreadPool library in Python that has, for example, a pool.execute (function, args) method that should be blocked when the pool is full (until one of the threads is free)?
I tried to use ThreadPool from the multiprocessing package, but its pool.apply_async () function does not block when the pool is full. In fact, I don't understand his behavior at all.
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3 answers
This ActiveState Code Recipes page has a Python queue based implementation to do blocking. Use add_task
wherever you are execute
.
## {{{ http://code.activestate.com/recipes/577187/ (r9)
from Queue import Queue
from threading import Thread
class Worker(Thread):
"""Thread executing tasks from a given tasks queue"""
def __init__(self, tasks):
Thread.__init__(self)
self.tasks = tasks
self.daemon = True
self.start()
def run(self):
while True:
func, args, kargs = self.tasks.get()
try: func(*args, **kargs)
except Exception, e: print e
self.tasks.task_done()
class ThreadPool:
"""Pool of threads consuming tasks from a queue"""
def __init__(self, num_threads):
self.tasks = Queue(num_threads)
for _ in range(num_threads): Worker(self.tasks)
def add_task(self, func, *args, **kargs):
"""Add a task to the queue"""
self.tasks.put((func, args, kargs))
def wait_completion(self):
"""Wait for completion of all the tasks in the queue"""
self.tasks.join()
if __name__ == '__main__':
from random import randrange
delays = [randrange(1, 10) for i in range(100)]
from time import sleep
def wait_delay(d):
print 'sleeping for (%d)sec' % d
sleep(d)
# 1) Init a Thread pool with the desired number of threads
pool = ThreadPool(20)
for i, d in enumerate(delays):
# print the percentage of tasks placed in the queue
print '%.2f%c' % ((float(i)/float(len(delays)))*100.0,'%')
# 2) Add the task to the queue
pool.add_task(wait_delay, d)
# 3) Wait for completion
pool.wait_completion()
## end of http://code.activestate.com/recipes/577187/ }}}
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I modified @ckhan's answer and added a callback function.
#Custom ThreadPool implementation from http://code.activestate.com/recipes/577187/
# Usage:
# def worker_method(data):
# ''' do processing '''
# return data
#
# def on_complete_callback(data, isfailed):
# print ('on complete %s' % data)
#
# pool = ThreadPool(5)
# for data in range(1,10)
# pool.add_task(worker_method, on_complete_callback, data)
# pool.wait_completion()
from Queue import Queue
from threading import Thread
import thread
class Worker(Thread):
"""Thread executing tasks from a given tasks queue"""
def __init__(self, tasks, thread_id):
Thread.__init__(self)
self.tasks = tasks
self.daemon = True
self.start()
self.thread_id = thread_id
def run(self):
while True:
func, callback, args, kargs = self.tasks.get()
try:
data = func(*args, **kargs)
callback(data, False)
except Exception, e:
callback(e, True)
self.tasks.task_done()
class ThreadPool:
"""Pool of threads consuming tasks from a queue"""
def __init__(self, num_threads):
self.tasks = Queue(num_threads)
for i in range(num_threads): Worker(self.tasks, i)
def add_task(self, func, callback, *args, **kargs):
"""Add a task to the queue"""
self.tasks.put((func, callback, args, kargs))
def wait_completion(self):
"""Wait for completion of all the tasks in the queue"""
self.tasks.join()
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