31 lines
1.1 KiB
Rust
31 lines
1.1 KiB
Rust
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//! Exponential backoff with jitter.
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//!
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//! Three use cases (subagent, provider, workflow) all share the same formula
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//! with different caps. This module provides a single implementation.
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use std::time::{Duration, SystemTime, UNIX_EPOCH};
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/// Compute an exponential backoff with ±25% jitter.
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///
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/// `attempt` is 0-based (first retry -> attempt=0 -> base=1s,
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/// second retry -> attempt=1 -> base=2s, etc.).
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/// `max_secs` sets the cap.
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pub fn backoff_seconds(attempt: u32, max_secs: u64) -> Duration {
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let base_secs = (2u64).pow(attempt).min(max_secs);
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let quarter = (base_secs * 250_000_000).max(100_000_000); // 25% of base, min 100ms
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let offset = jitter_ns(quarter);
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// ±25%: offset in [0, quarter), so result = base - quarter/2 + offset
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// which lies in [base - 25%, base + 25%).
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let ns = base_secs * 1_000_000_000 + offset - quarter / 2;
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Duration::from_nanos(ns)
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}
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/// Return a jitter offset in the range [0, range_ns).
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fn jitter_ns(range_ns: u64) -> u64 {
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let nanos = SystemTime::now()
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.duration_since(UNIX_EPOCH)
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.unwrap_or_default()
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.as_nanos() as u64;
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nanos % range_ns
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}
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