"""Custom implementation of multiprocessing.Pool with custom pickler. This module provides efficient ways of working with data stored in shared memory with numpy.memmap arrays without inducing any memory copy between the parent and child processes. This module should not be imported if multiprocessing is not available as it implements subclasses of multiprocessing Pool that uses a custom alternative to SimpleQueue. """ # Author: Olivier Grisel # Copyright: 2012, Olivier Grisel # License: BSD 3 clause import sys import warnings from time import sleep try: WindowsError except NameError: WindowsError = type(None) # Customizable pure Python pickler in Python 2 # customizable C-optimized pickler under Python 3.3+ from pickle import Pickler from pickle import HIGHEST_PROTOCOL from io import BytesIO from .disk import delete_folder from ._memmapping_reducer import get_memmapping_reducers from ._multiprocessing_helpers import mp, assert_spawning # We need the class definition to derive from it, not the multiprocessing.Pool # factory function from multiprocessing.pool import Pool try: import numpy as np except ImportError: np = None if sys.version_info[:2] > (2, 7): import copyreg ############################################################################### # Enable custom pickling in Pool queues class CustomizablePickler(Pickler): """Pickler that accepts custom reducers. HIGHEST_PROTOCOL is selected by default as this pickler is used to pickle ephemeral datastructures for interprocess communication hence no backward compatibility is required. `reducers` is expected to be a dictionary with key/values being `(type, callable)` pairs where `callable` is a function that give an instance of `type` will return a tuple `(constructor, tuple_of_objects)` to rebuild an instance out of the pickled `tuple_of_objects` as would return a `__reduce__` method. See the standard library documentation on pickling for more details. """ # We override the pure Python pickler as its the only way to be able to # customize the dispatch table without side effects in Python 2.7 # to 3.2. For Python 3.3+ leverage the new dispatch_table # feature from https://bugs.python.org/issue14166 that makes it possible # to use the C implementation of the Pickler which is faster. def __init__(self, writer, reducers=None, protocol=HIGHEST_PROTOCOL): Pickler.__init__(self, writer, protocol=protocol) if reducers is None: reducers = {} if hasattr(Pickler, 'dispatch'): # Make the dispatch registry an instance level attribute instead of # a reference to the class dictionary under Python 2 self.dispatch = Pickler.dispatch.copy() else: # Under Python 3 initialize the dispatch table with a copy of the # default registry self.dispatch_table = copyreg.dispatch_table.copy() for type, reduce_func in reducers.items(): self.register(type, reduce_func) def register(self, type, reduce_func): """Attach a reducer function to a given type in the dispatch table.""" if hasattr(Pickler, 'dispatch'): # Python 2 pickler dispatching is not explicitly customizable. # Let us use a closure to workaround this limitation. def dispatcher(self, obj): reduced = reduce_func(obj) self.save_reduce(obj=obj, *reduced) self.dispatch[type] = dispatcher else: self.dispatch_table[type] = reduce_func class CustomizablePicklingQueue(object): """Locked Pipe implementation that uses a customizable pickler. This class is an alternative to the multiprocessing implementation of SimpleQueue in order to make it possible to pass custom pickling reducers, for instance to avoid memory copy when passing memory mapped datastructures. `reducers` is expected to be a dict with key / values being `(type, callable)` pairs where `callable` is a function that, given an instance of `type`, will return a tuple `(constructor, tuple_of_objects)` to rebuild an instance out of the pickled `tuple_of_objects` as would return a `__reduce__` method. See the standard library documentation on pickling for more details. """ def __init__(self, context, reducers=None): self._reducers = reducers self._reader, self._writer = context.Pipe(duplex=False) self._rlock = context.Lock() if sys.platform == 'win32': self._wlock = None else: self._wlock = context.Lock() self._make_methods() def __getstate__(self): assert_spawning(self) return (self._reader, self._writer, self._rlock, self._wlock, self._reducers) def __setstate__(self, state): (self._reader, self._writer, self._rlock, self._wlock, self._reducers) = state self._make_methods() def empty(self): return not self._reader.poll() def _make_methods(self): self._recv = recv = self._reader.recv racquire, rrelease = self._rlock.acquire, self._rlock.release def get(): racquire() try: return recv() finally: rrelease() self.get = get if self._reducers: def send(obj): buffer = BytesIO() CustomizablePickler(buffer, self._reducers).dump(obj) self._writer.send_bytes(buffer.getvalue()) self._send = send else: self._send = send = self._writer.send if self._wlock is None: # writes to a message oriented win32 pipe are atomic self.put = send else: wlock_acquire, wlock_release = ( self._wlock.acquire, self._wlock.release) def put(obj): wlock_acquire() try: return send(obj) finally: wlock_release() self.put = put class PicklingPool(Pool): """Pool implementation with customizable pickling reducers. This is useful to control how data is shipped between processes and makes it possible to use shared memory without useless copies induces by the default pickling methods of the original objects passed as arguments to dispatch. `forward_reducers` and `backward_reducers` are expected to be dictionaries with key/values being `(type, callable)` pairs where `callable` is a function that, given an instance of `type`, will return a tuple `(constructor, tuple_of_objects)` to rebuild an instance out of the pickled `tuple_of_objects` as would return a `__reduce__` method. See the standard library documentation about pickling for more details. """ def __init__(self, processes=None, forward_reducers=None, backward_reducers=None, **kwargs): if forward_reducers is None: forward_reducers = dict() if backward_reducers is None: backward_reducers = dict() self._forward_reducers = forward_reducers self._backward_reducers = backward_reducers poolargs = dict(processes=processes) poolargs.update(kwargs) super(PicklingPool, self).__init__(**poolargs) def _setup_queues(self): context = getattr(self, '_ctx', mp) self._inqueue = CustomizablePicklingQueue(context, self._forward_reducers) self._outqueue = CustomizablePicklingQueue(context, self._backward_reducers) self._quick_put = self._inqueue._send self._quick_get = self._outqueue._recv class MemmappingPool(PicklingPool): """Process pool that shares large arrays to avoid memory copy. This drop-in replacement for `multiprocessing.pool.Pool` makes it possible to work efficiently with shared memory in a numpy context. Existing instances of numpy.memmap are preserved: the child suprocesses will have access to the same shared memory in the original mode except for the 'w+' mode that is automatically transformed as 'r+' to avoid zeroing the original data upon instantiation. Furthermore large arrays from the parent process are automatically dumped to a temporary folder on the filesystem such as child processes to access their content via memmapping (file system backed shared memory). Note: it is important to call the terminate method to collect the temporary folder used by the pool. Parameters ---------- processes: int, optional Number of worker processes running concurrently in the pool. initializer: callable, optional Callable executed on worker process creation. initargs: tuple, optional Arguments passed to the initializer callable. temp_folder: str, optional Folder to be used by the pool for memmapping large arrays for sharing memory with worker processes. If None, this will try in order: - a folder pointed by the JOBLIB_TEMP_FOLDER environment variable, - /dev/shm if the folder exists and is writable: this is a RAMdisk filesystem available by default on modern Linux distributions, - the default system temporary folder that can be overridden with TMP, TMPDIR or TEMP environment variables, typically /tmp under Unix operating systems. max_nbytes int or None, optional, 1e6 by default Threshold on the size of arrays passed to the workers that triggers automated memory mapping in temp_folder. Use None to disable memmapping of large arrays. mmap_mode: {'r+', 'r', 'w+', 'c'} Memmapping mode for numpy arrays passed to workers. See 'max_nbytes' parameter documentation for more details. forward_reducers: dictionary, optional Reducers used to pickle objects passed from master to worker processes: see below. backward_reducers: dictionary, optional Reducers used to pickle return values from workers back to the master process. verbose: int, optional Make it possible to monitor how the communication of numpy arrays with the subprocess is handled (pickling or memmapping) prewarm: bool or str, optional, "auto" by default. If True, force a read on newly memmapped array to make sure that OS pre-cache it in memory. This can be useful to avoid concurrent disk access when the same data array is passed to different worker processes. If "auto" (by default), prewarm is set to True, unless the Linux shared memory partition /dev/shm is available and used as temp folder. `forward_reducers` and `backward_reducers` are expected to be dictionaries with key/values being `(type, callable)` pairs where `callable` is a function that give an instance of `type` will return a tuple `(constructor, tuple_of_objects)` to rebuild an instance out of the pickled `tuple_of_objects` as would return a `__reduce__` method. See the standard library documentation on pickling for more details. """ def __init__(self, processes=None, temp_folder=None, max_nbytes=1e6, mmap_mode='r', forward_reducers=None, backward_reducers=None, verbose=0, context_id=None, prewarm=False, **kwargs): if context_id is not None: warnings.warn('context_id is deprecated and ignored in joblib' ' 0.9.4 and will be removed in 0.11', DeprecationWarning) forward_reducers, backward_reducers, self._temp_folder = \ get_memmapping_reducers( id(self), temp_folder=temp_folder, max_nbytes=max_nbytes, mmap_mode=mmap_mode, forward_reducers=forward_reducers, backward_reducers=backward_reducers, verbose=verbose, prewarm=prewarm) poolargs = dict( processes=processes, forward_reducers=forward_reducers, backward_reducers=backward_reducers) poolargs.update(kwargs) super(MemmappingPool, self).__init__(**poolargs) def terminate(self): n_retries = 10 for i in range(n_retries): try: super(MemmappingPool, self).terminate() break except OSError as e: if isinstance(e, WindowsError): # Workaround occasional "[Error 5] Access is denied" issue # when trying to terminate a process under windows. sleep(0.1) if i + 1 == n_retries: warnings.warn("Failed to terminate worker processes in" " multiprocessing pool: %r" % e) delete_folder(self._temp_folder)