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Code RoomMetrics registry deadlocks
HardPrep Room Coding #2045

Metrics registry deadlocks

Code reviewConcurrencySenior–Staff~32 min

Review this Java metrics registry. `record` is the hot path; it lazily creates a counter under a read lock then upgrades to write.

What a strong answer looks like

Separate real bugs from style. Rank issues by severity, point at the root cause rather than the symptom, and suggest a concrete fix, specific and kind.

0:00 of about 32 min
Mark a line and say what kind of problem it is.0 findings
1private final ReadWriteLock rw = new ReentrantReadWriteLock();
2private final Map<String, AtomicLong> counters = new HashMap<>();
3 
4void record(String name) {
5 rw.readLock().lock();
6 if (!counters.containsKey(name)) {
7 rw.writeLock().lock(); // upgrade
8 counters.put(name, new AtomicLong());
9 rw.writeLock().unlock();
10 }
11 counters.get(name).incrementAndGet();
12 rw.readLock().unlock();
13}
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