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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`memcpy` data race in `setobject.c`","articleBody":"# Bug report\n\nSeen when running locally. We should use the `ptr_wise_atomic_memmove` from `listobject.c`.\n\n```\nWARNING: ThreadSanitizer: data race (pid=833878)\n  Write of size 8 at 0x7fffb57ba460 by thread T10318:\n    #0 __tsan_memcpy \u003cnull\u003e (python+0xf4b62) (BuildId: 62048a720cd5edc7e743b66781182a91a8a5cb4a)\n    #1 set_swap_bodies /home/sgross/cpython/Objects/setobject.c:1465:9 (python+0x396739) (BuildId: 62048a720cd5edc7e743b66781182a91a8a5cb4a)\n    #2 set_intersection_update /home/sgross/cpython/Objects/setobject.c:1740:5 (python+0x391a91) (BuildId: 62048a720cd5edc7e743b66781182a91a8a5cb4a)\n    #3 set_iand /home/sgross/cpython/Objects/setobject.c:1795:14 (python+0x391a91)\n...\n\n  Previous atomic read of size 8 at 0x7fffb57ba460 by thread T10317:\n    #0 _Py_atomic_load_ptr_acquire /home/sgross/cpython/./Include/cpython/pyatomic_gcc.h:557:18 (python+0x38bb7c) (BuildId: 62048a720cd5edc7e743b66781182a91a8a5cb4a)\n    #1 set_compare_threadsafe /home/sgross/cpython/Objects/setobject.c:100:26 (python+0x38bb7c)\n    #2 set_do_lookup /home/sgross/cpython/Objects/setobject.c:234:22 (python+0x38bb7c)\n    #3 set_lookkey_threadsafe /home/sgross/cpython/Objects/setobject.c:452:14 (python+0x38bb7c)\n    #4 set_contains_entry /home/sgross/cpython/Objects/setobject.c:566:12 (python+0x38bb7c)\n```\n\nhttps://github.com/python/cpython/blob/6536fab19410ce701575b553d381cf805d3ef323/Objects/setobject.c#L1463-L1467\n\nhttps://github.com/python/cpython/blob/6536fab19410ce701575b553d381cf805d3ef323/Objects/setobject.c#L96-L100\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-143114\n* gh-143127\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/colesbury","@type":"Person","name":"colesbury"},"datePublished":"2025-12-23T15:48:41.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/143100/cpython/issues/143100"}