Add multiprocessing to flexible_character_accuracy

qurator/dinglehopper/flexible_character_accuracy.py

@@ -13,12 +13,12 @@ Note that we deviated from the original algorithm at some places.
 
 import sys
 from collections import Counter
-from functools import lru_cache, reduce
+from functools import lru_cache, reduce, partial
 from itertools import product, takewhile
-from typing import List, Tuple, Optional
+from multiprocessing import cpu_count, get_context
+from typing import List, Tuple, Optional, Union
 
 from Levenshtein import editops
-from multimethod import multimethod
 
 from . import ExtractedText
 
@@ -38,45 +38,45 @@ else:
     )
 
 
-@multimethod
 def flexible_character_accuracy(
-    gt: ExtractedText, ocr: ExtractedText
+    gt: Union[str, ExtractedText],
+    ocr: Union[str, ExtractedText],
+    n_cpu: int = cpu_count(),
 ) -> Tuple[float, List[Match]]:
     """Calculate the flexible character accuracy.
 
     Reference: contains steps 1-7 of the flexible character accuracy algorithm.
 
-    :param gt: The ground truth ExtractedText object.
-    :param ocr: The ExtractedText object to compare the ground truth with.
-    :return: Score between 0 and 1 and match objects.
-    """
-    return flexible_character_accuracy(gt.text, ocr.text)
-
-
-@multimethod
-def flexible_character_accuracy(gt: str, ocr: str) -> Tuple[float, List[Match]]:
-    """Calculate the flexible character accuracy.
-
-    Reference: contains steps 1-7 of the flexible character accuracy algorithm.
-
     :param gt: The ground truth text.
     :param ocr: The text to compare the ground truth with.
+    :param n_cpu: numbers of cpus to use for multiprocessing.
     :return: Score between 0 and 1 and match objects.
     """
 
+    if isinstance(gt, ExtractedText):
+        gt = gt.text
+    if isinstance(ocr, ExtractedText):
+        ocr = ocr.text
+
     best_score = -sys.maxsize
     best_matches = []
     # TODO: should this be configurable?
-    combinations = product(
+    coeffs = (
+        Coefficients(
+            edit_dist=edit_dist, length_diff=length_diff, offset=offset, length=length
+        )
+        for edit_dist, length_diff, offset, length in product(
             range(15, 31, 5), range(0, 24, 3), range(0, 4, 1), range(0, 6, 1)
         )
-    # TODO: place to parallelize the algorithm?
-    for (edit_dist, length_diff, offset, length) in combinations:
-        coef = Coefficients(
-            edit_dist=edit_dist, length_diff=length_diff, offset=offset, length=length
     )
+    with get_context("spawn").Pool(processes=n_cpu) as pool:
         # Steps 1 - 6 of the flexible character accuracy algorithm.
-        matches = match_with_coefficients(gt, ocr, coef)
+        # We only use multiprocessing if we have more than 2 cpus available.
+        # Otherwise the overhead for creating processes and filling caches is too big.
+        map_fun = partial(pool.imap_unordered, chunksize=10) if n_cpu > 2 else map
+        for matches in map_fun(
+            partial(match_with_coefficients, gt=gt, ocr=ocr), coeffs
+        ):
             # Step 7 of the flexible character accuracy algorithm.
             score = character_accuracy_for_matches(matches)
             if score > best_score:
@@ -88,7 +88,7 @@ def flexible_character_accuracy(gt: str, ocr: str) -> Tuple[float, List[Match]]:
     return best_score, best_matches
 
 
-def match_with_coefficients(gt: str, ocr: str, coef: Coefficients) -> List[Match]:
+def match_with_coefficients(coef: Coefficients, gt: str, ocr: str) -> List[Match]:
     """Match ground truth with ocr and consider a given set of coefficients.
 
     Reference: contains steps 1 - 6 of the flexible character accuracy algorithm.

qurator/dinglehopper/tests/test_flexible_character_accuracy.py

@@ -104,7 +104,7 @@ def extended_case_to_text(gt, ocr):
 
 @pytest.mark.parametrize(CASE_ARGS, [*SIMPLE_CASES, *COMPLEX_CASES])
 def test_flexible_character_accuracy_str(gt, ocr, first_line_score, all_line_score):
-    score, _ = flexible_character_accuracy(gt, ocr)
+    score, _ = flexible_character_accuracy(gt, ocr, 1)
     assert score == pytest.approx(all_line_score)
 
 
@@ -132,7 +132,7 @@ def test_flexible_character_accuracy_xml(gt, ocr, first_line_score, all_line_sco
 
     gt_text = get_extracted_text(gt)
     ocr_text = get_extracted_text(ocr)
-    score, _ = flexible_character_accuracy(gt_text, ocr_text)
+    score, _ = flexible_character_accuracy(gt_text, ocr_text, 1)
     assert score == pytest.approx(all_line_score)
 
 
@@ -186,7 +186,7 @@ def test_flexible_character_accuracy(config, ocr):
     )
     expected_score = character_accuracy(expected_dist)
 
-    result, matches = flexible_character_accuracy(gt, ocr)
+    result, matches = flexible_character_accuracy(gt, ocr, 1)
     agg = reduce(
         lambda acc, match: acc + Counter(match.dist._asdict()), matches, Counter()
     )
@@ -201,7 +201,7 @@ def test_flexible_character_accuracy_extended(
 ):
     """Tests from figure 4 in the 10.1016/j.patrec.2020.02.003."""
     gt_sentence, ocr_sentence = extended_case_to_text(gt, ocr)
-    result, _ = flexible_character_accuracy(gt_sentence, ocr_sentence)
+    result, _ = flexible_character_accuracy(gt_sentence, ocr_sentence, 1)
     assert result == pytest.approx(all_line_score, abs=0.001)
 
 
@@ -210,7 +210,7 @@ def test_match_with_coefficients(gt, ocr, first_line_score, all_line_score):
     coef = Coefficients()
     if not isinstance(gt, str):
         gt, ocr = extended_case_to_text(gt, ocr)
-    matches = match_with_coefficients(gt, ocr, coef)
+    matches = match_with_coefficients(coef, gt, ocr)
     score = character_accuracy_for_matches(matches)
     assert score == pytest.approx(all_line_score, abs=0.001)