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Alternative attempt at fixing memleak by being explicit about copies by filmor · Pull Request #2722 · pythonnet/pythonnet · GitHub
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Alternative attempt at fixing memleak by being explicit about copies #2722

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Alternative attempt at fixing memleak by being explicit about copies #2722

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a305127
Fix MethodBinding/OverloadMapper memory leak (#691)
greateggsgreg May 9, 2026
7f8a247
Tighten leak-test threshold to 10% to actually fail the bug
greateggsgreg May 9, 2026
11bebe4
Bugfix and improvements
filmor May 11, 2026
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Tighten leak-test threshold to 10% to actually fail the bug 
The previous 90% threshold (0.9 MB/iter against a 1 MB allocation)
documented the issue but did not reproduce it: master leaks
~600-765 KB/iter, which the 0.9 MB threshold accepts as passing.

Drop the threshold to 10% (104 KB/iter). On the 2026-05-09 verification
run with Python 3.14 GIL on linux-aarch64:

  Without fix (master):   ~572-765 KB/iter (FAIL)
  With fix (this branch): ~-500 B/iter     (PASS)

Margin is roughly 6x in either direction across .NET 8 and .NET 10, so
the threshold cleanly separates buggy from fixed states without being
sensitive to GC noise.
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@greateggsgreg @filmor
greateggsgreg authored and filmor committed May 11, 2026
commit 7f8a2475f970313251eefba38f597f16b8077660
15 changes: 8 additions & 7 deletions tests/test_method.py
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Original file line number Diff line number Diff line change
Expand Up @@ -983,9 +983,10 @@ def test_getting_generic_method_binding_does_not_leak_memory(memory_usage_tracki
bytesAllocatedPerIteration = pow(2, 20) # 1MB
bytesLeakedPerIteration = processBytesDelta / iterations

# Allow 90% threshold - this shows the original issue is fixed, which leaks the full allocated bytes per iteration
# Increased from 50% to ensure that it works on Windows with Python >3.13
failThresholdBytesLeakedPerIteration = bytesAllocatedPerIteration * 0.9
# Tight 10% threshold: with the fix the per-iteration leak is essentially
# zero, while the bug retains the bulk of the 1 MB payload (~600 KB/iter
# on 3.14 GIL). 100 KB/iter cleanly distinguishes the two states.
failThresholdBytesLeakedPerIteration = bytesAllocatedPerIteration * 0.1

assert bytesLeakedPerIteration < failThresholdBytesLeakedPerIteration

Expand Down Expand Up @@ -1025,8 +1026,8 @@ def test_getting_overloaded_method_binding_does_not_leak_memory(memory_usage_tra
bytesAllocatedPerIteration = pow(2, 20) # 1MB
bytesLeakedPerIteration = processBytesDelta / iterations

# Allow 90% threshold - this shows the original issue is fixed, which leaks the full allocated bytes per iteration
failThresholdBytesLeakedPerIteration = bytesAllocatedPerIteration * 0.9
# Tight 10% threshold; see test_getting_generic_method_binding_does_not_leak_memory.
failThresholdBytesLeakedPerIteration = bytesAllocatedPerIteration * 0.1

assert bytesLeakedPerIteration < failThresholdBytesLeakedPerIteration

Expand Down Expand Up @@ -1068,8 +1069,8 @@ def test_getting_method_overloads_binding_does_not_leak_memory(memory_usage_trac
bytesAllocatedPerIteration = pow(2, 20) # 1MB
bytesLeakedPerIteration = processBytesDelta / iterations

# Allow 90% threshold - this shows the original issue is fixed, which leaks the full allocated bytes per iteration
failThresholdBytesLeakedPerIteration = bytesAllocatedPerIteration * 0.9
# Tight 10% threshold; see test_getting_generic_method_binding_does_not_leak_memory.
failThresholdBytesLeakedPerIteration = bytesAllocatedPerIteration * 0.1

assert bytesLeakedPerIteration < failThresholdBytesLeakedPerIteration

Expand Down
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