SoundPlayer.Play() does not preserve in-memory WAV buffer lifetime

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Issue 类型
缺陷
描述清晰度
描述清楚
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技术栈
csharp
领域
backend, desktop

调研方向

Start with src/libraries/System.Windows.Extensions/src/System/Media/SoundPlayer.cs, especially Play(), PlayLooping(), and the PlaySoundW import, to trace how _streamData is passed to asynchronous playback and how stopping or replacing playback is handled. Then find the related SoundPlayer tests and run them. Done means in-memory WAV data stays at a stable address until asynchronous playback completes or looping playback stops, while synchronous and file-path playback remain unaffected.

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描述

area-System.IO bug untriaged
Description

For Stream and non-file URL sources, SoundPlayer copies the WAV into its private _streamData array. Play() and PlayLooping() then call PlaySoundW with SND_MEMORY | SND_ASYNC (plus SND_LOOP for looping).

The generated [LibraryImport] stub pins the managed array only for the duration of the P/Invoke call. PlaySoundW returns immediately under SND_ASYNC, ending that pin while playback may still be using the buffer. The Win32 contract requires the buffer to remain valid until playback completes.

Required:  pin [ PlaySoundW call ---------------- playback complete/stop ]
Actual:    pin [ PlaySoundW call ] return ------- playback may continue
Why this is a product bug

This occurs through a supported public API path, such as new SoundPlayer(Stream).Play() or PlayLooping(). SoundPlayer allocates and owns the private _streamData copy, selects SND_MEMORY | SND_ASYNC, and initiates the native operation. The caller cannot access or pin _streamData, and Play() exposes no completion task or callback through which the caller could maintain its address.

The lifetime obligation therefore belongs to SoundPlayer: it must satisfy the downstream WinMM contract for the operation it chose. This is not caller misuse or a general thread-safety issue.

Impact

The generated P/Invoke pins _streamData only for the duration of the PlaySoundW call. Because SND_ASYNC returns when playback starts, WinMM may continue accessing the buffer after the pin is released.

The PlaySound contract requires a buffer used with SND_MEMORY | SND_ASYNC to remain valid until playback completes. A compacting GC can move _streamData, and replacing Stream can clear the final managed reference, allowing the array to be collected and its address reused while playback is active.

A diagnostic reproduction can observe the private array moving:

using var player = new SoundPlayer(new MemoryStream(wav, writable: false));
player.Load();
player.PlayLooping();

GC.Collect(
    GC.MaxGeneration,
    GCCollectionMode.Forced,
    blocking: true,
    compacting: true);

Private reflection is needed only to compare the array's address before and after the collection, not to create the underlying lifetime condition.

Expected behavior

Keep the in-memory WAV at a stable address until one-shot playback completes or looping playback is stopped, for example through a persistent pin or native-owned stable copy.

PlaySync() is not affected by this specific issue because PlaySoundW returns only after synchronous playback completes. File-path playback is also unaffected because Windows receives a filename rather than a managed WAV pointer.

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