Fix rare cases of corrupt feature flags in NDK reports #1801
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…on flag in the event_writer
…ring a write lock
Android notifier sizes
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kstenerud
approved these changes
Feb 7, 2023
bugsnag-plugin-android-ndk/src/main/jni/utils/serializer/event_writer.c
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Goal
Avoid reporting feature flags that were corrupted by being modified when a native crash was in progress.
Design
Added a new spin lock structure similar to a sequence-lock to protect the NDK-side feature flags. When altering feature flags its counter value will be odd (strictly
(counter & 1) != 0) and when no changes are taking place the value will be even (strictly(counter & 1) == 0).The signal handler takes a snapshot of the counter before and after writing the feature flags to the event dump. These two values are compared and a "verification" flag of one byte is written. If this value is zero (invalid) when loading the feature flags, all feature flags for the event are discarded (as they will have been corrupted).
This approach avoids the signal handler possibly having to wait on the lock, and avoids deadlocks.
Testing
Re-tested using a local saturation test.