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ASIO: collecting output_devices() into Vec only returns the first device #1106
Description
Summary
On Windows ASIO, host.output_devices() behaves differently depending on whether the iterator is collected first.
- Iterating directly prints all devices.
- Collecting into
Vec<_>first, then iterating, only prints the first device.
collect should not change the visible device set.
Environment
- cpal:
0.17.1 - OS: Windows (x64)
- Backend: ASIO (
cpal::HostId::Asio) - Devices in my setup:
Focusrite USB ASIORealtek ASIOUSB DAC ASIO
Minimal Repro
use anyhow::Result;
use cpal::traits::{DeviceTrait, HostTrait};
fn list_output_devices() -> Result<()> {
let host = cpal::host_from_id(cpal::HostId::Asio)?;
let devices = host.output_devices()?;
// let devices = devices.collect::<Vec<_>>();
for device in devices {
println!("{}", device.description()?);
}
Ok(())
}
fn main() -> Result<()> {
list_output_devices()
}Actual Behavior
Without collect:
Focusrite USB ASIO
Realtek ASIO
USB DAC ASIO
With:
let devices = devices.collect::<Vec<_>>();Only the first device is printed:
Focusrite USB ASIO
Expected Behavior
Both versions should enumerate the same set of devices (all 3 in this environment).
Related
Possibly related to ASIO enumeration/lifetime behavior in #798 (this repro is single-threaded and triggered by collecting Device values).
Activity
roderickvd commentedon Feb 18, 2026
Thanks for the report. This is due to ASIO only allowing one driver being loaded at a time. Please try out #1107.
roderickvd commentedon Feb 23, 2026
@mikai233 sorry, I went ahead merging #1107 because I mistakenly thought that you had already confirmed it works. Let me know if it does or doesn't.
mikai233 commentedon Feb 24, 2026
Hi @roderickvd — sorry for the late reply. I’ve been busy with my project and didn’t get a chance to follow up in time.
I retested on the latest master after the fix was merged:
cpal v0.18.0 (https://github.com/RustAudio/cpal.git#1c64e49c) (from cargo tree -i cpal)Windows + ASIO
On my side, the enumeration is still missing one device, and now it happens both when iterating directly and when collecting into a Vec first (so the behavior is consistent, but still incomplete).
Current output:
fix(asio): enumerate devices without known sample rate
roderickvd commentedon Feb 24, 2026
No worries, thanks for the feedback. Please try #1112.
(I don't have ASIO so I am doing this purely from a code standpoint, please bear with me.)
mikai233 commentedon Feb 25, 2026
@roderickvd, I've tested the new fix and confirmed it works well both when iterating and when collecting into a Vec on the minimal reproducible example. I've also tested it in my music player, and it works perfectly there too. Thanks for the fix!
fix(asio): enumerate devices without known sample rate (RustAudio#1112)