from __future__ import annotations import json import logging from abc import abstractmethod from pathlib import Path from typing import TYPE_CHECKING, Any, cast from warnings import warn # working around https://github.com/sphinx-doc/sphinx/issues/10400 from twisted.internet.defer import Deferred # noqa: TC002 from scrapy.exceptions import ScrapyDeprecationWarning from scrapy.spiders import Spider # noqa: TC001 from scrapy.utils.job import job_dir from scrapy.utils.misc import build_from_crawler, load_object from scrapy.utils.python import global_object_name if TYPE_CHECKING: # requires queuelib >= 1.6.2 from queuelib.queue import BaseQueue # typing.Self requires Python 3.11 from typing_extensions import Self from scrapy.crawler import Crawler from scrapy.dupefilters import BaseDupeFilter from scrapy.http.request import Request from scrapy.pqueues import ScrapyPriorityQueue from scrapy.statscollectors import StatsCollector logger = logging.getLogger(__name__) class BaseSchedulerMeta(type): """ Metaclass to check scheduler classes against the necessary interface """ def __instancecheck__(cls, instance: Any) -> bool: return cls.__subclasscheck__(type(instance)) def __subclasscheck__(cls, subclass: type) -> bool: return ( hasattr(subclass, "has_pending_requests") and callable(subclass.has_pending_requests) and hasattr(subclass, "enqueue_request") and callable(subclass.enqueue_request) and hasattr(subclass, "next_request") and callable(subclass.next_request) ) class BaseScheduler(metaclass=BaseSchedulerMeta): """The scheduler component is responsible for storing requests received from the engine, and feeding them back upon request (also to the engine). The original sources of said requests are: * Spider: ``start`` method, requests created for URLs in the ``start_urls`` attribute, request callbacks * Spider middleware: ``process_spider_output`` and ``process_spider_exception`` methods * Downloader middleware: ``process_request``, ``process_response`` and ``process_exception`` methods The order in which the scheduler returns its stored requests (via the ``next_request`` method) plays a great part in determining the order in which those requests are downloaded. See :ref:`request-order`. The methods defined in this class constitute the minimal interface that the Scrapy engine will interact with. """ @classmethod def from_crawler(cls, crawler: Crawler) -> Self: """ Factory method which receives the current :class:`~scrapy.crawler.Crawler` object as argument. """ return cls() def open(self, spider: Spider) -> Deferred[None] | None: """ Called when the spider is opened by the engine. It receives the spider instance as argument and it's useful to execute initialization code. :param spider: the spider object for the current crawl :type spider: :class:`~scrapy.spiders.Spider` """ def close(self, reason: str) -> Deferred[None] | None: """ Called when the spider is closed by the engine. It receives the reason why the crawl finished as argument and it's useful to execute cleaning code. :param reason: a string which describes the reason why the spider was closed :type reason: :class:`str` """ @abstractmethod def has_pending_requests(self) -> bool: """ ``True`` if the scheduler has enqueued requests, ``False`` otherwise """ raise NotImplementedError @abstractmethod def enqueue_request(self, request: Request) -> bool: """ Process a request received by the engine. Return ``True`` if the request is stored correctly, ``False`` otherwise. If ``False``, the engine will fire a ``request_dropped`` signal, and will not make further attempts to schedule the request at a later time. For reference, the default Scrapy scheduler returns ``False`` when the request is rejected by the dupefilter. """ raise NotImplementedError @abstractmethod def next_request(self) -> Request | None: """ Return the next :class:`~scrapy.Request` to be processed, or ``None`` to indicate that there are no requests to be considered ready at the moment. Returning ``None`` implies that no request from the scheduler will be sent to the downloader in the current reactor cycle. The engine will continue calling ``next_request`` until ``has_pending_requests`` is ``False``. """ raise NotImplementedError class Scheduler(BaseScheduler): """Default scheduler. Requests are stored into priority queues (:setting:`SCHEDULER_PRIORITY_QUEUE`) that sort requests by :attr:`~scrapy.http.Request.priority`. By default, a single, memory-based priority queue is used for all requests. When using :setting:`JOBDIR`, a disk-based priority queue is also created, and only unserializable requests are stored in the memory-based priority queue. For a given priority value, requests in memory take precedence over requests in disk. Each priority queue stores requests in separate internal queues, one per priority value. The memory priority queue uses :setting:`SCHEDULER_MEMORY_QUEUE` queues, while the disk priority queue uses :setting:`SCHEDULER_DISK_QUEUE` queues. The internal queues determine :ref:`request order ` when requests have the same priority. :ref:`Start requests ` are stored into separate internal queues by default, and :ref:`ordered differently `. Duplicate requests are filtered out with an instance of :setting:`DUPEFILTER_CLASS`. .. _request-order: Request order ============= With default settings, pending requests are stored in a LIFO_ queue (:ref:`except for start requests `). As a result, crawling happens in `DFO order`_, which is usually the most convenient crawl order. However, you can enforce :ref:`BFO ` or :ref:`a custom order ` (:ref:`except for the first few requests `). .. _LIFO: https://en.wikipedia.org/wiki/Stack_(abstract_data_type) .. _DFO order: https://en.wikipedia.org/wiki/Depth-first_search .. _start-request-order: Start request order ------------------- :ref:`Start requests ` are sent in the order they are yielded from :meth:`~scrapy.Spider.start`, and given the same :attr:`~scrapy.http.Request.priority`, other requests take precedence over start requests. You can set :setting:`SCHEDULER_START_MEMORY_QUEUE` and :setting:`SCHEDULER_START_DISK_QUEUE` to ``None`` to handle start requests the same as other requests when it comes to order and priority. .. _bfo: Crawling in BFO order --------------------- If you do want to crawl in `BFO order`_, you can do it by setting the following :ref:`settings `: | :setting:`DEPTH_PRIORITY` = ``1`` | :setting:`SCHEDULER_DISK_QUEUE` = ``"scrapy.squeues.PickleFifoDiskQueue"`` | :setting:`SCHEDULER_MEMORY_QUEUE` = ``"scrapy.squeues.FifoMemoryQueue"`` .. _BFO order: https://en.wikipedia.org/wiki/Breadth-first_search .. _custom-request-order: Crawling in a custom order -------------------------- You can manually set :attr:`~scrapy.http.Request.priority` on requests to force a specific request order. .. _concurrency-v-order: Concurrency affects order ------------------------- While pending requests are below the configured values of :setting:`CONCURRENT_REQUESTS`, :setting:`CONCURRENT_REQUESTS_PER_DOMAIN` or :setting:`CONCURRENT_REQUESTS_PER_IP`, those requests are sent concurrently. As a result, the first few requests of a crawl may not follow the desired order. Lowering those settings to ``1`` enforces the desired order except for the very first request, but it significantly slows down the crawl as a whole. """ @classmethod def from_crawler(cls, crawler: Crawler) -> Self: dupefilter_cls = load_object(crawler.settings["DUPEFILTER_CLASS"]) return cls( dupefilter=build_from_crawler(dupefilter_cls, crawler), jobdir=job_dir(crawler.settings), dqclass=load_object(crawler.settings["SCHEDULER_DISK_QUEUE"]), mqclass=load_object(crawler.settings["SCHEDULER_MEMORY_QUEUE"]), logunser=crawler.settings.getbool("SCHEDULER_DEBUG"), stats=crawler.stats, pqclass=load_object(crawler.settings["SCHEDULER_PRIORITY_QUEUE"]), crawler=crawler, ) def __init__( self, dupefilter: BaseDupeFilter, jobdir: str | None = None, dqclass: type[BaseQueue] | None = None, mqclass: type[BaseQueue] | None = None, logunser: bool = False, stats: StatsCollector | None = None, pqclass: type[ScrapyPriorityQueue] | None = None, crawler: Crawler | None = None, ): """Initialize the scheduler. :param dupefilter: An object responsible for checking and filtering duplicate requests. The value for the :setting:`DUPEFILTER_CLASS` setting is used by default. :type dupefilter: :class:`scrapy.dupefilters.BaseDupeFilter` instance or similar: any class that implements the `BaseDupeFilter` interface :param jobdir: The path of a directory to be used for persisting the crawl's state. The value for the :setting:`JOBDIR` setting is used by default. See :ref:`topics-jobs`. :type jobdir: :class:`str` or ``None`` :param dqclass: A class to be used as persistent request queue. The value for the :setting:`SCHEDULER_DISK_QUEUE` setting is used by default. :type dqclass: class :param mqclass: A class to be used as non-persistent request queue. The value for the :setting:`SCHEDULER_MEMORY_QUEUE` setting is used by default. :type mqclass: class :param logunser: A boolean that indicates whether or not unserializable requests should be logged. The value for the :setting:`SCHEDULER_DEBUG` setting is used by default. :type logunser: bool :param stats: A stats collector object to record stats about the request scheduling process. The value for the :setting:`STATS_CLASS` setting is used by default. :type stats: :class:`scrapy.statscollectors.StatsCollector` instance or similar: any class that implements the `StatsCollector` interface :param pqclass: A class to be used as priority queue for requests. The value for the :setting:`SCHEDULER_PRIORITY_QUEUE` setting is used by default. :type pqclass: class :param crawler: The crawler object corresponding to the current crawl. :type crawler: :class:`scrapy.crawler.Crawler` """ self.df: BaseDupeFilter = dupefilter self.dqdir: str | None = self._dqdir(jobdir) self.pqclass: type[ScrapyPriorityQueue] | None = pqclass self.dqclass: type[BaseQueue] | None = dqclass self.mqclass: type[BaseQueue] | None = mqclass self.logunser: bool = logunser self.stats: StatsCollector | None = stats self.crawler: Crawler | None = crawler self._sdqclass: type[BaseQueue] | None = self._get_start_queue_cls( crawler, "DISK" ) self._smqclass: type[BaseQueue] | None = self._get_start_queue_cls( crawler, "MEMORY" ) def _get_start_queue_cls( self, crawler: Crawler | None, queue: str ) -> type[BaseQueue] | None: if crawler is None: return None cls = crawler.settings[f"SCHEDULER_START_{queue}_QUEUE"] if not cls: return None return load_object(cls) def has_pending_requests(self) -> bool: return len(self) > 0 def open(self, spider: Spider) -> Deferred[None] | None: """ (1) initialize the memory queue (2) initialize the disk queue if the ``jobdir`` attribute is a valid directory (3) return the result of the dupefilter's ``open`` method """ self.spider: Spider = spider self.mqs: ScrapyPriorityQueue = self._mq() self.dqs: ScrapyPriorityQueue | None = self._dq() if self.dqdir else None return self.df.open() def close(self, reason: str) -> Deferred[None] | None: """ (1) dump pending requests to disk if there is a disk queue (2) return the result of the dupefilter's ``close`` method """ if self.dqs is not None: state = self.dqs.close() assert isinstance(self.dqdir, str) self._write_dqs_state(self.dqdir, state) return self.df.close(reason) def enqueue_request(self, request: Request) -> bool: """ Unless the received request is filtered out by the Dupefilter, attempt to push it into the disk queue, falling back to pushing it into the memory queue. Increment the appropriate stats, such as: ``scheduler/enqueued``, ``scheduler/enqueued/disk``, ``scheduler/enqueued/memory``. Return ``True`` if the request was stored successfully, ``False`` otherwise. """ if not request.dont_filter and self.df.request_seen(request): self.df.log(request, self.spider) return False dqok = self._dqpush(request) assert self.stats is not None if dqok: self.stats.inc_value("scheduler/enqueued/disk", spider=self.spider) else: self._mqpush(request) self.stats.inc_value("scheduler/enqueued/memory", spider=self.spider) self.stats.inc_value("scheduler/enqueued", spider=self.spider) return True def next_request(self) -> Request | None: """ Return a :class:`~scrapy.Request` object from the memory queue, falling back to the disk queue if the memory queue is empty. Return ``None`` if there are no more enqueued requests. Increment the appropriate stats, such as: ``scheduler/dequeued``, ``scheduler/dequeued/disk``, ``scheduler/dequeued/memory``. """ request: Request | None = self.mqs.pop() assert self.stats is not None if request is not None: self.stats.inc_value("scheduler/dequeued/memory", spider=self.spider) else: request = self._dqpop() if request is not None: self.stats.inc_value("scheduler/dequeued/disk", spider=self.spider) if request is not None: self.stats.inc_value("scheduler/dequeued", spider=self.spider) return request def __len__(self) -> int: """ Return the total amount of enqueued requests """ return len(self.dqs) + len(self.mqs) if self.dqs is not None else len(self.mqs) def _dqpush(self, request: Request) -> bool: if self.dqs is None: return False try: self.dqs.push(request) except ValueError as e: # non serializable request if self.logunser: msg = ( "Unable to serialize request: %(request)s - reason:" " %(reason)s - no more unserializable requests will be" " logged (stats being collected)" ) logger.warning( msg, {"request": request, "reason": e}, exc_info=True, extra={"spider": self.spider}, ) self.logunser = False assert self.stats is not None self.stats.inc_value("scheduler/unserializable", spider=self.spider) return False return True def _mqpush(self, request: Request) -> None: self.mqs.push(request) def _dqpop(self) -> Request | None: if self.dqs is not None: return self.dqs.pop() return None def _mq(self) -> ScrapyPriorityQueue: """Create a new priority queue instance, with in-memory storage""" assert self.crawler assert self.pqclass try: return build_from_crawler( self.pqclass, self.crawler, downstream_queue_cls=self.mqclass, key="", start_queue_cls=self._smqclass, ) except TypeError: warn( f"The __init__ method of {global_object_name(self.pqclass)} " f"does not support a `start_queue_cls` keyword-only " f"parameter.", ScrapyDeprecationWarning, ) return build_from_crawler( self.pqclass, self.crawler, downstream_queue_cls=self.mqclass, key="", ) def _dq(self) -> ScrapyPriorityQueue: """Create a new priority queue instance, with disk storage""" assert self.crawler assert self.dqdir assert self.pqclass state = self._read_dqs_state(self.dqdir) try: q = build_from_crawler( self.pqclass, self.crawler, downstream_queue_cls=self.dqclass, key=self.dqdir, startprios=state, start_queue_cls=self._sdqclass, ) except TypeError: warn( f"The __init__ method of {global_object_name(self.pqclass)} " f"does not support a `start_queue_cls` keyword-only " f"parameter.", ScrapyDeprecationWarning, ) q = build_from_crawler( self.pqclass, self.crawler, downstream_queue_cls=self.dqclass, key=self.dqdir, startprios=state, ) if q: logger.info( "Resuming crawl (%(queuesize)d requests scheduled)", {"queuesize": len(q)}, extra={"spider": self.spider}, ) return q def _dqdir(self, jobdir: str | None) -> str | None: """Return a folder name to keep disk queue state at""" if jobdir: dqdir = Path(jobdir, "requests.queue") if not dqdir.exists(): dqdir.mkdir(parents=True) return str(dqdir) return None def _read_dqs_state(self, dqdir: str) -> list[int]: path = Path(dqdir, "active.json") if not path.exists(): return [] with path.open(encoding="utf-8") as f: return cast(list[int], json.load(f)) def _write_dqs_state(self, dqdir: str, state: list[int]) -> None: with Path(dqdir, "active.json").open("w", encoding="utf-8") as f: json.dump(state, f)