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Edit File: threadpool.py
# -*- test-case-name: twisted.test.test_threadpool -*- # Copyright (c) Twisted Matrix Laboratories. # See LICENSE for details. """ twisted.python.threadpool: a pool of threads to which we dispatch tasks. In most cases you can just use C{reactor.callInThread} and friends instead of creating a thread pool directly. """ from threading import Thread, current_thread from typing import List from twisted._threads import pool as _pool from twisted.python import context, log from twisted.python.deprecate import deprecated from twisted.python.failure import Failure from twisted.python.versions import Version WorkerStop = object() class ThreadPool: """ This class (hopefully) generalizes the functionality of a pool of threads to which work can be dispatched. L{callInThread} and L{stop} should only be called from a single thread. @ivar started: Whether or not the thread pool is currently running. @type started: L{bool} @ivar threads: List of workers currently running in this thread pool. @type threads: L{list} @ivar _pool: A hook for testing. @type _pool: callable compatible with L{_pool} """ min = 5 max = 20 joined = False started = False name = None threadFactory = Thread currentThread = staticmethod( deprecated( version=Version("Twisted", 22, 1, 0), replacement="threading.current_thread", )(current_thread) ) _pool = staticmethod(_pool) def __init__(self, minthreads=5, maxthreads=20, name=None): """ Create a new threadpool. @param minthreads: minimum number of threads in the pool @type minthreads: L{int} @param maxthreads: maximum number of threads in the pool @type maxthreads: L{int} @param name: The name to give this threadpool; visible in log messages. @type name: native L{str} """ assert minthreads >= 0, "minimum is negative" assert minthreads <= maxthreads, "minimum is greater than maximum" self.min = minthreads self.max = maxthreads self.name = name self.threads: List[Thread] = [] def trackingThreadFactory(*a, **kw): thread = self.threadFactory( # type: ignore[misc] *a, name=self._generateName(), **kw ) self.threads.append(thread) return thread def currentLimit(): if not self.started: return 0 return self.max self._team = self._pool(currentLimit, trackingThreadFactory) @property def workers(self): """ For legacy compatibility purposes, return a total number of workers. @return: the current number of workers, both idle and busy (but not those that have been quit by L{ThreadPool.adjustPoolsize}) @rtype: L{int} """ stats = self._team.statistics() return stats.idleWorkerCount + stats.busyWorkerCount @property def working(self): """ For legacy compatibility purposes, return the number of busy workers as expressed by a list the length of that number. @return: the number of workers currently processing a work item. @rtype: L{list} of L{None} """ return [None] * self._team.statistics().busyWorkerCount @property def waiters(self): """ For legacy compatibility purposes, return the number of idle workers as expressed by a list the length of that number. @return: the number of workers currently alive (with an allocated thread) but waiting for new work. @rtype: L{list} of L{None} """ return [None] * self._team.statistics().idleWorkerCount @property def _queue(self): """ For legacy compatibility purposes, return an object with a C{qsize} method that indicates the amount of work not yet allocated to a worker. @return: an object with a C{qsize} method. """ class NotAQueue: def qsize(q): """ Pretend to be a Python threading Queue and return the number of as-yet-unconsumed tasks. @return: the amount of backlogged work not yet dispatched to a worker. @rtype: L{int} """ return self._team.statistics().backloggedWorkCount return NotAQueue() q = _queue # Yes, twistedchecker, I want a single-letter # attribute name. def start(self): """ Start the threadpool. """ self.joined = False self.started = True # Start some threads. self.adjustPoolsize() backlog = self._team.statistics().backloggedWorkCount if backlog: self._team.grow(backlog) def startAWorker(self): """ Increase the number of available workers for the thread pool by 1, up to the maximum allowed by L{ThreadPool.max}. """ self._team.grow(1) def _generateName(self): """ Generate a name for a new pool thread. @return: A distinctive name for the thread. @rtype: native L{str} """ return f"PoolThread-{self.name or id(self)}-{self.workers}" def stopAWorker(self): """ Decrease the number of available workers by 1, by quitting one as soon as it's idle. """ self._team.shrink(1) def __setstate__(self, state): setattr(self, "__dict__", state) ThreadPool.__init__(self, self.min, self.max) def __getstate__(self): state = {} state["min"] = self.min state["max"] = self.max return state def callInThread(self, func, *args, **kw): """ Call a callable object in a separate thread. @param func: callable object to be called in separate thread @param args: positional arguments to be passed to C{func} @param kw: keyword args to be passed to C{func} """ self.callInThreadWithCallback(None, func, *args, **kw) def callInThreadWithCallback(self, onResult, func, *args, **kw): """ Call a callable object in a separate thread and call C{onResult} with the return value, or a L{twisted.python.failure.Failure} if the callable raises an exception. The callable is allowed to block, but the C{onResult} function must not block and should perform as little work as possible. A typical action for C{onResult} for a threadpool used with a Twisted reactor would be to schedule a L{twisted.internet.defer.Deferred} to fire in the main reactor thread using C{.callFromThread}. Note that C{onResult} is called inside the separate thread, not inside the reactor thread. @param onResult: a callable with the signature C{(success, result)}. If the callable returns normally, C{onResult} is called with C{(True, result)} where C{result} is the return value of the callable. If the callable throws an exception, C{onResult} is called with C{(False, failure)}. Optionally, C{onResult} may be L{None}, in which case it is not called at all. @param func: callable object to be called in separate thread @param args: positional arguments to be passed to C{func} @param kw: keyword arguments to be passed to C{func} """ if self.joined: return ctx = context.theContextTracker.currentContext().contexts[-1] def inContext(): try: result = inContext.theWork() # type: ignore[attr-defined] ok = True except BaseException: result = Failure() ok = False inContext.theWork = None # type: ignore[attr-defined] if inContext.onResult is not None: # type: ignore[attr-defined] inContext.onResult(ok, result) # type: ignore[attr-defined] inContext.onResult = None # type: ignore[attr-defined] elif not ok: log.err(result) # Avoid closing over func, ctx, args, kw so that we can carefully # manage their lifecycle. See # test_threadCreationArgumentsCallInThreadWithCallback. inContext.theWork = lambda: context.call( # type: ignore[attr-defined] ctx, func, *args, **kw ) inContext.onResult = onResult # type: ignore[attr-defined] self._team.do(inContext) def stop(self): """ Shutdown the threads in the threadpool. """ self.joined = True self.started = False self._team.quit() for thread in self.threads: thread.join() def adjustPoolsize(self, minthreads=None, maxthreads=None): """ Adjust the number of available threads by setting C{min} and C{max} to new values. @param minthreads: The new value for L{ThreadPool.min}. @param maxthreads: The new value for L{ThreadPool.max}. """ if minthreads is None: minthreads = self.min if maxthreads is None: maxthreads = self.max assert minthreads >= 0, "minimum is negative" assert minthreads <= maxthreads, "minimum is greater than maximum" self.min = minthreads self.max = maxthreads if not self.started: return # Kill of some threads if we have too many. if self.workers > self.max: self._team.shrink(self.workers - self.max) # Start some threads if we have too few. if self.workers < self.min: self._team.grow(self.min - self.workers) def dumpStats(self): """ Dump some plain-text informational messages to the log about the state of this L{ThreadPool}. """ log.msg(f"waiters: {self.waiters}") log.msg(f"workers: {self.working}") log.msg(f"total: {self.threads}")