On Fri, 8 Apr 2022 06:49:09 GMT, Maxim Kartashev <d...@openjdk.java.net> wrote:
>> These crashes were not reproducible, so the fix is based on a hypothesis >> that there are two possible reasons for them: >> 1. `makeDefaultConfig()` returning `NULL`. >> 2. A race condition when the number of screens changes. >> The race scenario: `X11GraphisDevice.makeDefaultConfiguration()` is called >> on EDT so the call can race with `X11GraphisDevice.invalidate()` that >> re-sets the screen number of the device; the latter is invoked on the >> `AWT-XAWT` thread from `X11GraphicsEnvironment.rebuildDevices()`. So by the >> time `makeDefaultConfiguration()` makes a native call with the device's >> current screen number, the `x11Screens` array maintained by the native code >> could have become shorter. And the native methods like >> `Java_sun_awt_X11GraphicsDevice_getConfigColormap()` assume that the number >> passed to them is always current and valid. The AWT lock only protects >> against the changes during the native methods invocation and does not >> protect against them being called with an outdated screen number. With a >> larger screen number, those methods read past the end of the `x11Screens` >> array. >> >> The fix for (1) is to die gracefully instead of crashing in an attempt to >> de-reference a `NULL` pointer, which might happen upon returning from >> `makeDefaultConfig()` in `getAllConfigs()`. >> >> The fix for (2) is to eliminate the race by protecting >> `X11GraphisDevice.screen` with the AWT lock such that it doesn't change when >> the native methods working with it are active. >> >> We've been shipping JetBrains Runtime with this fix for a few months now and >> there were no crash reports with those specific patterns against the >> versions with the fix. > > Maxim Kartashev has updated the pull request incrementally with one > additional commit since the last revision: > > Restored the original code in X11GraphicsDevice.java that got auto-formatted Marked as reviewed by prr (Reviewer). ------------- PR: https://git.openjdk.java.net/jdk/pull/7182
