Fixes a critical data race where resetVidMap() was writing to the vidMap
pointer while other methods were reading it concurrently without synchronization.
Changes:
- Removed embedded *vidMap from MasterClient
- Added vidMapLock (sync.RWMutex) to protect vidMap pointer access
- Created safe accessor methods (GetLocations, GetDataCenter, etc.)
- Updated all direct vidMap accesses to use thread-safe methods
- Updated resetVidMap() to acquire write lock during pointer swap
The vidMap already has internal locking for its operations, but this fix
protects the vidMap pointer itself from concurrent read/write races.
Verified with: go test -race ./weed/wdclient/...
Impact:
- Prevents potential panics from concurrent pointer access
- No performance impact - uses RWMutex for read-heavy workloads
- Maintains backward compatibility through wrapper methods
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