# Copyright 2011  Lars Wirzenius
# 
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# 
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.


import multiprocessing
import Queue
import time


def worker(func, requests, results): # pragma: no cover
    while True:
        item = requests.get()
        if item is None:
            break
        request = item[0]
        result = func(request)
        results.put(result)


class BackgroundProcessing(object):

    '''Manage background processing queues.'''
    
    def __init__(self, func, numprocs=None):
        self.pending = 0
        self.requests = multiprocessing.Queue()
        self.results = multiprocessing.Queue()
        args = (func, self.requests, self.results)
        n = numprocs or multiprocessing.cpu_count()
        self.processes = [multiprocessing.Process(target=worker, args=args)
                          for i in range(n)]
        for p in self.processes:
            p.start()
        
    def enqueue_request(self, request):
        '''Put a request into queue, to be processed by workers whenever.'''
        self.pending += 1
        self.requests.put((request,))
        
    def close_requests(self):
        '''Signal workers that they can retire.
        
        All pending requests will be processed, but after the queue
        is empty, the workers will finish. No more requests may be
        enqueued.
        
        '''
        for p in self.processes:
            self.requests.put(None)

    def finish(self):
        '''Wait until all children have finished.'''
        for p in self.processes:
            p.join()
        
    def get_results(self, block=False):
        '''Return currently available results.
        
        If 'block' is True, then wait until there is at least one
        result.
        
        '''

        if block and self.pending == 0:
            return []

        items = []
        while True:
            try:
                item = self.results.get(block)
            except Queue.Empty:
                break
            else:
                self.pending -= 1
                items.append(item)
                block = False
        return items