lib: Make random number generation thread safe #6480
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| Original file line number | Diff line number | Diff line change |
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| """Test of gis library lrand48 PRNG thread-safety | ||
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| @author Maris Nartiss | ||
| @author Gemini | ||
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| @copyright 2025 by the GRASS Development Team | ||
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| @license This program is free software under the GNU General Public License (>=v2). | ||
| Read the file COPYING that comes with GRASS | ||
| for details | ||
| """ | ||
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| import ctypes | ||
| import threading | ||
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| from grass.gunittest.case import TestCase | ||
| from grass.gunittest.main import test | ||
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| from grass.lib.gis import G_srand48, G_lrand48 | ||
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| class Lrand48ThreadSafetyTestCase(TestCase): | ||
| """Test case for lrand48 thread-safety and reproducibility.""" | ||
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| def test_thread_safety_and_reproducibility(self): | ||
| """Verify that multi-threaded execution produces the same set of | ||
| random numbers as single-threaded execution.""" | ||
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| seed = 1337 | ||
| num_values = 10000 | ||
| num_threads = 4 | ||
| values_per_thread = num_values // num_threads | ||
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| self.assertEqual( | ||
| num_values % num_threads, | ||
| 0, | ||
| "Total number of values must be divisible by the number of threads.", | ||
| ) | ||
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| # --- Define ctypes function signatures --- | ||
| G_srand48.argtypes = [ctypes.c_long] | ||
| G_srand48.restype = None | ||
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| G_lrand48.argtypes = [] | ||
| G_lrand48.restype = ctypes.c_long | ||
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Member
There was a problem hiding this comment. Isn't this ctypesgen job? Isn't that already done? |
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| # --- 1. Single-threaded execution --- | ||
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Member
There was a problem hiding this comment. While often seen in generated code, I think our experience is that these ASCII comment graphic is hard to maintain and inherently inconsistent (thinking about old code we cleaned in GRASS). |
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| list_single = [] | ||
| G_srand48(seed) | ||
| for _ in range(num_values): | ||
| list_single.append(G_lrand48()) | ||
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| # --- 2. Multi-threaded execution --- | ||
| list_multi_raw = [] | ||
| lock = threading.Lock() | ||
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| def worker(): | ||
| """Calls G_lrand48 and appends the result to a shared list.""" | ||
| local_results = [] | ||
| for _ in range(values_per_thread): | ||
| # G_lrand48() itself is protected by a C-level mutex | ||
| local_results.append(G_lrand48()) | ||
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| # Use a Python-level lock to safely extend the shared list | ||
| with lock: | ||
| list_multi_raw.extend(local_results) | ||
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| # Reset the seed to ensure the sequence starts from the beginning | ||
| G_srand48(seed) | ||
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| threads = [] | ||
| for _ in range(num_threads): | ||
| thread = threading.Thread(target=worker) | ||
| threads.append(thread) | ||
| thread.start() | ||
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| for thread in threads: | ||
| thread.join() | ||
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| # --- 3. Verification --- | ||
| self.assertEqual( | ||
| len(list_single), | ||
| len(list_multi_raw), | ||
| "Single-threaded and multi-threaded runs produced a different number of values.", | ||
| ) | ||
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| # Check for duplicates in the multi-threaded list. The presence of duplicates | ||
| # would indicate that the C-level mutex failed and multiple threads | ||
| # received the same random number. | ||
| self.assertEqual( | ||
| len(list_multi_raw), | ||
| len(set(list_multi_raw)), | ||
| "Duplicate values found in multi-threaded run, indicating a race condition.", | ||
| ) | ||
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| # The sorted lists of numbers must be identical. | ||
| # This confirms that although threads ran in parallel, the C-level mutex | ||
| # correctly serialized access to the PRNG, yielding the exact same | ||
| # block of numbers. | ||
| self.assertListEqual( | ||
| sorted(list_single), | ||
| sorted(list_multi_raw), | ||
| "The set of generated numbers differs between single-threaded and multi-threaded runs.", | ||
| ) | ||
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| if __name__ == "__main__": | ||
| test() | ||
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No need. Human author is, or at least should be, the owner of the code in ways which matter to us. Approach to copyright differs in between countries and I would not even venture into it.
If there is a important provenance info, it should go to the commit message (and/or PR description).
We will not be inviting Gemini to a code sprint or to join the development team, nor expecting more insights into a code it generated comparing to any other code.