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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`concurrent.futures.Executor.map` temporarily exceeds its `buffersize` while collecting the next result","articleBody":"# Bug report\n\n### Bug description:\n\nPotential follow up after the merge of #125663 (introduce `buffersize` param in `Executor.map`).\n\n**\"Bug\": `concurrent.futures.Executor.map` temporarily exceeds its `buffersize` while collecting the next result:**\n\nLet's define:\n```python\nresults: Iterator = executor.map(fn, iterable, buffersize=buffersize)\n```\n\n**What happens when calling `next(results)`:**\n1. fetch the next `arg` from `interable` and put a task for `fn(arg)` in the buffer\n2. wait for next result to be available\n3. yield the collected result\n\nSo during step 2. the buffer's size is actually `buffersize + 1`.\n\nIf we want a strict guarantee that there is at most `buffersize` concurrent tasks even during a `next`, we have to **swap step 1. and step 2.**\n\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\n_No response_\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-131467\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/ebonnal","@type":"Person","name":"ebonnal"},"datePublished":"2025-03-19T15:53:38.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/131466/cpython/issues/131466"}