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ASIO: TimeBase treats small backward steps in systemTime as timeGetTime wraps, so stream instants race ahead and overflow after ~10 minutes

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@chrischaps 已经在做这个了。

开始于 2026年10月11日。

  • #1396 来自 @chrischaps —— 未关闭

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3/5
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1-2 天
新手友好度
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Issue 类型
缺陷
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技术栈
rust
领域
backend

调研方向

Start with TimeBase::to_stream_instant in src/host/asio/stream.rs and inspect how it distinguishes clock wraparound from backward jitter. The report includes a Focusrite ASIO reproduction and suggests checking callback timestamps for large jumps. Done means genuine wraps are handled without treating small backward steps as wraps, and callback instants avoid overflow; an open pull request is already linked.

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描述

host - asio platform - windows

cpal: 0.18.2, asio feature. Driver: Focusrite USB ASIO 4.150.0.432, Scarlett 2i2 1st Gen, 128-frame buffers at 48 kHz, Windows 11.

What happens

TimeBase::to_stream_instant (src/host/asio/stream.rs) treats any ns < prev as a timeGetTime() wrap, and adds TIMEGETIME_WRAP_NS (about 49.7 days) to the epoch:

let prev = self.last_ns.swap(ns, Ordering::Relaxed);
let epoch = if ns < prev {
    self.epoch_ns.fetch_add(TIMEGETIME_WRAP_NS, Ordering::Relaxed) + TIMEGETIME_WRAP_NS
} else { ... };
StreamInstant::from_nanos(epoch + ns)

Focusrite's ASIOTimeInfo::systemTime jitters: from one buffer switch to the next it sometimes steps back by tens to hundreds of microseconds. Over 10 s (3,746 callbacks) I counted 78 such steps, between 17 µs and 667 µs back. The normal step between callbacks ranged from 2.4 µs to 4.7 ms, against the nominal 2.67 ms. Each backward step adds 49.7 days, so:

  • the callback instant reaches about 10 years after 10 s;
  • epoch + ns overflows u64 after about 10 minutes. In a debug build this panics on the audio thread. In release it wraps.

Around that point, the latency an app reads as playback.checked_duration_since(callback) came out as about 1.6 × 10¹⁶ µs.

Suggested fix

Only count a wrap when the step back is large: a real timeGetTime wrap goes back by nearly 2³² ms. For example:

let epoch = if ns < prev && prev - ns > TIMEGETIME_WRAP_NS / 2 { /* wrap */ } else { /* jitter: keep epoch */ };

Optionally, clamp so the instant never runs backwards (max(prev_instant, new)) to keep instants monotonic through the jitter.

Repro

Build an output stream on the Focusrite USB ASIO driver. Log info.timestamp().callback for each callback, and look for callback-to-callback deltas of about 4.29 × 10¹⁵ ns.

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  3. Fork 仓库，在一个分支上完成修改。
  4. 提交 Pull Request，并在描述里引用这个 Issue 编号。

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