mirror of https://github.com/scrapy/scrapy.git
301 lines
10 KiB
Python
301 lines
10 KiB
Python
"""
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This is the Scrapy engine which controls the Scheduler, Downloader and Spiders.
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For more information see docs/topics/architecture.rst
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"""
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from time import time
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from twisted.internet import reactor, defer
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from twisted.python.failure import Failure
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from scrapy import log, signals
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from scrapy.stats import stats
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from scrapy.core.downloader import Downloader
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from scrapy.core.scraper import Scraper
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from scrapy.exceptions import DontCloseSpider
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from scrapy.http import Response, Request
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from scrapy.utils.misc import load_object
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from scrapy.utils.signal import send_catch_log, send_catch_log_deferred
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from scrapy.utils.defer import mustbe_deferred
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class Slot(object):
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def __init__(self):
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self.closing = False
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self.inprogress = set() # requests in progress
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def add_request(self, request):
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self.inprogress.add(request)
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def remove_request(self, request):
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self.inprogress.remove(request)
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self._maybe_fire_closing()
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def close(self):
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self.closing = defer.Deferred()
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self._maybe_fire_closing()
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return self.closing
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def _maybe_fire_closing(self):
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if self.closing and not self.inprogress:
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self.closing.callback(None)
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class ExecutionEngine(object):
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def __init__(self, settings, spider_closed_callback):
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self.settings = settings
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self.slots = {}
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self.running = False
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self.paused = False
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self._next_request_calls = {}
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self.scheduler = load_object(settings['SCHEDULER'])()
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self.downloader = Downloader()
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self.scraper = Scraper(self, self.settings)
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self._spider_closed_callback = spider_closed_callback
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@defer.inlineCallbacks
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def start(self):
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"""Start the execution engine"""
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assert not self.running, "Engine already running"
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self.start_time = time()
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yield send_catch_log_deferred(signal=signals.engine_started)
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self.running = True
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def stop(self):
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"""Stop the execution engine gracefully"""
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assert self.running, "Engine not running"
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self.running = False
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dfd = self._close_all_spiders()
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return dfd.addBoth(lambda _: self._finish_stopping_engine())
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def pause(self):
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"""Pause the execution engine"""
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self.paused = True
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def unpause(self):
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"""Resume the execution engine"""
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self.paused = False
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def is_idle(self):
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return self.scheduler.is_idle() and self.downloader.is_idle() and \
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self.scraper.is_idle()
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def next_request(self, spider, now=False):
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"""Scrape the next request for the spider passed.
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The next request to be scraped is retrieved from the scheduler and
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requested from the downloader.
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The spider is closed if there are no more pages to scrape.
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"""
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if now:
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self._next_request_calls.pop(spider, None)
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elif spider not in self._next_request_calls:
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call = reactor.callLater(0, self.next_request, spider, now=True)
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self._next_request_calls[spider] = call
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return call
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else:
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return
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if self.paused:
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return reactor.callLater(5, self.next_request, spider)
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while not self._needs_backout(spider):
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if not self._next_request(spider):
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break
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if self.spider_is_idle(spider):
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self._spider_idle(spider)
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def _needs_backout(self, spider):
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slot = self.slots[spider]
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return not self.running \
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or slot.closing \
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or self.spider_is_closed(spider) \
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or self.downloader.sites[spider].needs_backout() \
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or self.scraper.sites[spider].needs_backout()
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def _next_request(self, spider):
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request = self.scheduler.next_request(spider)
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if not request:
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return
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d = self._download(request, spider)
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d.addBoth(self._handle_downloader_output, request, spider)
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d.addErrback(log.msg, spider=spider)
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slot = self.slots[spider]
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d.addBoth(lambda _: slot.remove_request(request))
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d.addErrback(log.msg, spider=spider)
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d.addBoth(lambda _: self.next_request(spider))
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return d
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def _handle_downloader_output(self, response, request, spider):
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assert isinstance(response, (Request, Response, Failure)), response
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# downloader middleware can return requests (for example, redirects)
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if isinstance(response, Request):
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self.crawl(response, spider)
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return
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# response is a Response or Failure
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d = defer.Deferred()
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d.addBoth(self.scraper.enqueue_scrape, request, spider)
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d.addErrback(log.err, spider=spider)
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if isinstance(response, Failure):
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d.errback(response)
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else:
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d.callback(response)
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return d
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def spider_is_idle(self, spider):
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scraper_idle = spider in self.scraper.sites \
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and self.scraper.sites[spider].is_idle()
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pending = self.scheduler.spider_has_pending_requests(spider)
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downloading = spider in self.downloader.sites \
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and self.downloader.sites[spider].active
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return scraper_idle and not (pending or downloading)
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def spider_is_closed(self, spider):
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"""Return True if the spider is fully closed (ie. not even in the
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closing stage)"""
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return spider not in self.downloader.sites
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@property
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def open_spiders(self):
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return self.downloader.sites.keys()
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def has_capacity(self):
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"""Does the engine have capacity to handle more spiders"""
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return len(self.downloader.sites) < self.downloader.concurrent_spiders
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def crawl(self, request, spider):
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assert spider in self.open_spiders, \
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"Spider %r not opened when crawling: %s" % (spider.name, request)
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self.schedule(request, spider)
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self.next_request(spider)
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def schedule(self, request, spider):
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return self.scheduler.enqueue_request(spider, request)
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def download(self, request, spider):
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slot = self.slots[spider]
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slot.add_request(request)
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if isinstance(request, Response):
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return request
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d = self._download(request, spider)
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d.addCallback(self.download, spider)
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d.addBoth(self._remove_request, slot, request)
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return d
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def _remove_request(self, _, slot, request):
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slot.remove_request(request)
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return _
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def _download(self, request, spider):
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slot = self.slots[spider]
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slot.add_request(request)
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def _on_success(response):
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"""handle the result of a page download"""
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assert isinstance(response, (Response, Request))
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if isinstance(response, Response):
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response.request = request # tie request to response received
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log.msg(log.formatter.crawled(request, response, spider), \
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level=log.DEBUG, spider=spider)
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send_catch_log(signal=signals.response_received, \
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response=response, request=request, spider=spider)
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return response
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def _on_complete(_):
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self.next_request(spider)
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return _
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dwld = mustbe_deferred(self.downloader.fetch, request, spider)
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dwld.addCallback(_on_success)
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dwld.addBoth(_on_complete)
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return dwld
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@defer.inlineCallbacks
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def open_spider(self, spider):
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assert self.has_capacity(), "No free spider slots when opening %r" % \
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spider.name
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log.msg("Spider opened", spider=spider)
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self.slots[spider] = Slot()
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yield self.scheduler.open_spider(spider)
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self.downloader.open_spider(spider)
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yield self.scraper.open_spider(spider)
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stats.open_spider(spider)
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yield send_catch_log_deferred(signals.spider_opened, spider=spider)
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self.next_request(spider)
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def _spider_idle(self, spider):
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"""Called when a spider gets idle. This function is called when there
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are no remaining pages to download or schedule. It can be called
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multiple times. If some extension raises a DontCloseSpider exception
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(in the spider_idle signal handler) the spider is not closed until the
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next loop and this function is guaranteed to be called (at least) once
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again for this spider.
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"""
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res = send_catch_log(signal=signals.spider_idle, \
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spider=spider, dont_log=DontCloseSpider)
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if any(isinstance(x, Failure) and isinstance(x.value, DontCloseSpider) \
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for _, x in res):
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reactor.callLater(5, self.next_request, spider)
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return
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if self.spider_is_idle(spider):
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self.close_spider(spider, reason='finished')
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def close_spider(self, spider, reason='cancelled'):
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"""Close (cancel) spider and clear all its outstanding requests"""
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slot = self.slots[spider]
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if slot.closing:
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return slot.closing
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log.msg("Closing spider (%s)" % reason, spider=spider)
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self.scheduler.clear_pending_requests(spider)
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dfd = slot.close()
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dfd.addBoth(lambda _: self.downloader.close_spider(spider))
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dfd.addErrback(log.err, spider=spider)
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dfd.addBoth(lambda _: self.scraper.close_spider(spider))
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dfd.addErrback(log.err, spider=spider)
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dfd.addBoth(lambda _: self.scheduler.close_spider(spider))
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dfd.addErrback(log.err, spider=spider)
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dfd.addBoth(lambda _: self._cancel_next_call(spider))
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dfd.addErrback(log.err, spider=spider)
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dfd.addBoth(lambda _: send_catch_log_deferred(signal=signals.spider_closed, \
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spider=spider, reason=reason))
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dfd.addErrback(log.err, spider=spider)
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dfd.addBoth(lambda _: stats.close_spider(spider, reason=reason))
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dfd.addErrback(log.err, spider=spider)
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dfd.addBoth(lambda _: log.msg("Spider closed (%s)" % reason, spider=spider))
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dfd.addBoth(lambda _: self.slots.pop(spider))
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dfd.addErrback(log.err, spider=spider)
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dfd.addBoth(lambda _: self._spider_closed_callback(spider))
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return dfd
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def _cancel_next_call(self, spider):
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call = self._next_request_calls.pop(spider, None)
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if call and call.active:
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call.cancel()
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def _close_all_spiders(self):
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dfds = [self.close_spider(s, reason='shutdown') for s in self.open_spiders]
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dlist = defer.DeferredList(dfds)
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return dlist
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@defer.inlineCallbacks
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def _finish_stopping_engine(self):
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yield send_catch_log_deferred(signal=signals.engine_stopped)
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yield stats.engine_stopped()
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