⚡ Optimize DeflateEncoder to safely avoid zero-filling output buffers#378
⚡ Optimize DeflateEncoder to safely avoid zero-filling output buffers#378
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Replaced `unsafe { output.set_len(bound) }` with the safer `output.clear()`, `output.try_reserve(bound)`, and `output.spare_capacity_mut()` pattern. This avoids the undefined behavior of creating references to uninitialized memory while maintaining the performance benefit of skipping zero-initialization.
Benchmark results (Stream Processing):
- Baseline (resize with 0): ~810 MiB/s
- Optimized (safe pattern): ~973 MiB/s
- Improvement: ~20% throughput increase.
Co-authored-by: 404Setup <[email protected]>
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404Setup
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💡 What:
Replaced the potentially unsafe
output.set_len(bound)pattern (which was previously optimized fromresize(bound, 0)) with a safer, idiomatic Rust pattern usingoutput.clear(),output.try_reserve(bound), andoutput.spare_capacity_mut(). This allowsDeflateEncoderto write directly to uninitialized memory without exposing it as initialized data before it is written.🎯 Why:
Zero-filling the output buffer (
resize(bound, 0)) is a performance bottleneck for high-throughput compression. The previous optimization attempt usedunsafe { set_len(bound) }on uninitialized memory, which technically triggers Undefined Behavior (UB) because it exposes uninitialized memory as valid&[u8]. The new approach usesspare_capacity_mut()to provide a&mut [MaybeUninit<u8>]slice to the compressor, which is both safe (no UB) and performant.📊 Measured Improvement:
Benchmark:
cargo bench --bench bench_main "Stream Processing"resize(bound, 0)): ~810 MiB/s (1.23 ms)spare_capacity_mut): ~973 MiB/s (1.02 ms)This confirms that the safer implementation maintains the high performance of avoiding zero-initialization while adhering to Rust's safety guarantees.
PR created automatically by Jules for task 14984143046502692767 started by @404Setup