[x270880x]

Problem

GlStreamInterface.draw() takes a snapshot of the extra preview surfaces with multiPreviewSurfaceManagers.values.toList(). For a collection of exactly one element, Kotlin's toList() reads size and then calls iterator().next() as a separate step. If that surface is removed from another thread in between (in our app removeMultiPreviewSurface() is called from the main thread, while draw() runs on the GL thread), the iterator is already empty and next() throws NoSuchElementException. Without a RenderErrorCallback the exception is rethrown on the GL thread and the app crashes.

With two or more surfaces toList() already copies through an ArrayList, so only the common case of one extra preview is affected.

We hit this in production with 2.8.0 (the same line, 346 there): first as a crash on a Samsung Galaxy S24 Ultra (Android 16), and, after we set a RenderErrorCallback that skips the frame, again on a Vivo phone (Android 16). In both cases the exception came from the ConcurrentHashMap iterator inside toList() in draw().

Change

Take the snapshot with ArrayList(multiPreviewSurfaceManagers.values). ArrayList copies through ConcurrentHashMap's toArray(), which tolerates concurrent changes, so a surface removed meanwhile is simply in or out of this frame's snapshot, as already happens with two or more surfaces. One line, plus a comment so it isn't changed back to toList().

Testing

• ./gradlew :library:compileReleaseKotlin and ./gradlew :library:testDebugUnitTest (22 tests) pass locally.
• A throwaway JVM loop, not included in the PR: one thread keeps removing and re-adding the only entry of a ConcurrentHashMap, another snapshots values the way draw() does. This is an artificial worst case, only to show the mechanism: toList() threw NoSuchElementException 1,839,677 times in 6,835,364 snapshots in 5 s; ArrayList(values) threw 0 times in 29,150,687.
• Not run on a device: the window is tiny, and on a phone it only shows up occasionally.

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