Limit concurrent HTTP requests #922
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Reworked this to reduce the boilerplate and ensure the semaphore permit is held until the response is fully consumed. Hopefully that doesn't confuse the import? |
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Ralith
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| .inspect(move |_| { | ||
| // Ensure we keep a concurrent request permit alive until the stream is consumed | ||
| let _guard = &semaphore_guard; | ||
| }) |
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This is a little cheeky and might be clearer as a stream transformer struct, but that would probably take about 4x as much code. Let me know if that'd be preferred.
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When building a non-trivial project with third-party dependencies fetched via
http_archiveor similar, e.g. from reindeer in non-vendored mode, buck2 can generate extremely large numbers of outgoing HTTP requests. Hyper does not enforce any limits itself, happily expanding its connection pool with every additional concurrent request. This can cause the remote HTTP server to reject requests, and even lead to buck2 itself failing with "too many open files" errors.Larger numbers of concurrent requests have rapidly diminishing returns, so while there's no obviously correct limit, any smallish number should improve behavior in most cases. It may even improve total throughput by reducing contention for network bandwidth.
See also discussion in facebookincubator/reindeer#46.