[BUG] Issue with multi-threading when using blur filtering

[tnnandi]

Description

To Reproduce

Steps to reproduce the behavior:

1. Choose 'blur' for qc in the tile extraction step:

dataset.extract_tiles(qc='blur', #  ‘otsu’, ‘blur’, ‘both’, or None  # qc.GaussianV2()
                      save_tiles=True,
                      save_tfrecords=True,
                      skip_extracted=False,
                      max_tiles = 200,)

           INFO     Extracting tiles from 34 slides (tile_px=256, tile_um=9.9x)
           INFO     Using 64 processes (pool=fork)
           INFO     No ROI for TCGA-86-6562-01Z-00-DX1.5dea3015-e606-4837-9f99-ac14f0aa091b, using whole slide.
Speed:  ?
Extracting... ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━   0%  0/34 ● -:--:--[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 50: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 51: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 51: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 52: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 52: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 53: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 53: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 54: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 54: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 55: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 55: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 56: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 56: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 57: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 57: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 58: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 58: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 59: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 59: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 60: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 60: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 61: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 61: Can't spawn new thread: res = 11
[ERROR:[email protected]] global parallel_impl.cpp:244 WorkerThread 62: Can't spawn new thread: res = 11
[07:31:39] INFO     Finished tile extraction for TCGA-86-6562 (200 tiles of 2953 possible)
           INFO     No ROI for TCGA-86-7711-01Z-00-DX1.f64dd9d8-b9ca-4d1f-9783-d1042979132d, using whole slide.
Speed:  571 img/s
Extracting... ━╺━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━   3%  1/34 ● -:--:--
Traceback (most recent call last):
  File "/lus/eagle/clone/g2/projects/GeomicVar/tarak/multimodal_learning_T1/preprocessing/slideflow_preprocessing.py", line 45, in <module>
    dataset.extract_tiles(qc='blur', #  ‘otsu’, ‘blur’, ‘both’, or None  # qc.GaussianV2()
  File "/lus/eagle/clone/g2/projects/GeomicVar/tarak/multimodal_learning_T1/slideflow/slideflow/slideflow_scratch_env/lib/python3.9/site-packages/slideflow/dataset.py", line 1762, in extract_tiles
    wsi = _prepare_slide(
  File "/lus/eagle/clone/g2/projects/GeomicVar/tarak/multimodal_learning_T1/slideflow/slideflow/slideflow_scratch_env/lib/python3.9/site-packages/slideflow/dataset.py", line 140, in _prepare_slide
    slide.qc(method=qc, **qc_kwargs)
  File "/lus/eagle/clone/g2/projects/GeomicVar/tarak/multimodal_learning_T1/slideflow/slideflow/slideflow_scratch_env/lib/python3.9/site-packages/slideflow/slide/wsi.py", line 2552, in qc
    mask = qc(self)
  File "/lus/eagle/clone/g2/projects/GeomicVar/tarak/multimodal_learning_T1/slideflow/slideflow/slideflow_scratch_env/lib/python3.9/site-packages/slideflow/slide/qc/gaussian_v2.py", line 125, in __call__
    blur_mask = super().__call__(wsi)
  File "/lus/eagle/clone/g2/projects/GeomicVar/tarak/multimodal_learning_T1/slideflow/slideflow/slideflow_scratch_env/lib/python3.9/site-packages/slideflow/slide/qc/strided_qc.py", line 379, in __call__
    if self.filter_pool is not None:
  File "/lus/eagle/clone/g2/projects/GeomicVar/tarak/multimodal_learning_T1/slideflow/slideflow/slideflow_scratch_env/lib/python3.9/site-packages/slideflow/slide/qc/strided_qc.py", line 255, in filter_pool
    self._filter_pool = mp.dummy.Pool(self.filter_threads)
  File "/lus/eagle/clone/g2/projects/GeomicVar/tarak/multimodal_learning_T1/slideflow/slideflow/slideflow_scratch_env/lib/python3.9/multiprocessing/dummy/__init__.py", line 124, in Pool
    return ThreadPool(processes, initializer, initargs)
  File "/lus/eagle/clone/g2/projects/GeomicVar/tarak/multimodal_learning_T1/slideflow/slideflow/slideflow_scratch_env/lib/python3.9/multiprocessing/pool.py", line 927, in __init__
    Pool.__init__(self, processes, initializer, initargs)
  File "/lus/eagle/clone/g2/projects/GeomicVar/tarak/multimodal_learning_T1/slideflow/slideflow/slideflow_scratch_env/lib/python3.9/multiprocessing/pool.py", line 250, in __init__
    self._result_handler.start()
  File "/lus/eagle/clone/g2/projects/GeomicVar/tarak/multimodal_learning_T1/slideflow/slideflow/slideflow_scratch_env/lib/python3.9/threading.py", line 899, in start
    _start_new_thread(self._bootstrap, ())
RuntimeError: can't start new thread
Exception in thread Thread-1:
Traceback (most recent call last):
  File "/lus/eagle/clone/g2/projects/GeomicVar/tarak/multimodal_learning_T1/slideflow/slideflow/slideflow_scratch_env/lib/python3.9/threading.py", line 980, in _bootstrap_inner
    self.run()
  File "/lus/eagle/clone/g2/projects/GeomicVar/tarak/multimodal_learning_T1/slideflow/slideflow/slideflow_scratch_env/lib/python3.9/threading.py", line 917, in run
    self._target(*self._args, **self._kwargs)
  File "/lus/eagle/clone/g2/projects/GeomicVar/tarak/multimodal_learning_T1/slideflow/slideflow/slideflow_scratch_env/lib/python3.9/multiprocessing/managers.py", line 194, in accepter
    t.start()
  File "/lus/eagle/clone/g2/projects/GeomicVar/tarak/multimodal_learning_T1/slideflow/slideflow/slideflow_scratch_env/lib/python3.9/threading.py", line 899, in start
    _start_new_thread(self._bootstrap, ())
RuntimeError: can't start new thread

Expected behavior

Environment:

• Slideflow Version (e.g., 1.0): 2.3.1
• OS (e.g., Ubuntu):
• How you installed Slideflow (pip, source): Tried using both 'pip install' and install from source
• Python version: 3.9
• CUDA/cuDNN version: 12.1
• GPU models and configuration: A100
• Any other relevant information:

Additional context

The issue doesn't arise when 'blur' isn't used (e.g., qc='otsu')