Source code for

# Copyright 2020 - 2021 MONAI Consortium
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
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# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
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from queue import Empty, Full, Queue
from threading import Thread

from import DataLoader, Dataset

[docs]class ThreadBuffer: """ Iterates over values from self.src in a separate thread but yielding them in the current thread. This allows values to be queued up asynchronously. The internal thread will continue running so long as the source has values or until the stop() method is called. One issue raised by using a thread in this way is that during the lifetime of the thread the source object is being iterated over, so if the thread hasn't finished another attempt to iterate over it will raise an exception or yield unexpected results. To ensure the thread releases the iteration and proper cleanup is done the stop() method must be called which will join with the thread. Args: src: Source data iterable buffer_size: Number of items to buffer from the source timeout: Time to wait for an item from the buffer, or to wait while the buffer is full when adding items """ def __init__(self, src, buffer_size=1, timeout=0.01): self.src = src self.buffer_size = buffer_size self.timeout = timeout self.buffer = Queue(self.buffer_size) self.gen_thread = None self.is_running = False def enqueue_values(self): for src_val in self.src: while self.is_running: try: self.buffer.put(src_val, timeout=self.timeout) except Full: pass # try to add the item again else: break # successfully added the item, quit trying else: # quit the thread cleanly when requested to stop break def stop(self): self.is_running = False # signal the thread to exit if self.gen_thread is not None: self.gen_thread.join() self.gen_thread = None def __iter__(self): self.is_running = True self.gen_thread = Thread(target=self.enqueue_values, daemon=True) self.gen_thread.start() try: while self.is_running and (self.gen_thread.is_alive() or not self.buffer.empty()): try: yield self.buffer.get(timeout=self.timeout) except Empty: pass # queue was empty this time, try again finally: self.stop() # ensure thread completion
class ThreadDataLoader(DataLoader): """ Subclass of `DataLoader` using a `ThreadBuffer` object to implement `__iter__` method asynchronously. This will iterate over data from the loader as expected however the data is generated on a separate thread. Use this class where a `DataLoader` instance is required and not just an iterable object. """ def __init__(self, dataset: Dataset, num_workers: int = 0, **kwargs): super().__init__(dataset, num_workers, **kwargs) # ThreadBuffer will use the inherited __iter__ instead of the one defined below self.buffer = ThreadBuffer(super().__iter__()) def __iter__(self): yield from self.buffer