smengcl commented on code in PR #10988:
URL: https://github.com/apache/ozone/pull/10988#discussion_r3755439599
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hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/volume/MutableVolumeSet.java:
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@@ -421,6 +432,36 @@ public StorageLocationReport[] getStorageReport() {
}
}
+ /**
+ * Lock-free variant of {@link #getStorageReport()}. Both {@code volumeMap}
+ * and {@code failedVolumeMap} are {@link ConcurrentHashMap}s, so this
returns
+ * a weakly-consistent snapshot (mirroring {@link #getVolumesList()}) without
+ * acquiring the volume-set lock.
+ *
+ * <p>Use this from callers that must not block on the volume-set lock. In
+ * particular, metrics sampling runs while the {@code DefaultMetricsSystem}
+ * monitor is held, and a volume-failure handler holds the volume-set write
+ * lock while unregistering volume metrics (which needs that same monitor);
+ * acquiring the volume-set lock from the sampling thread can therefore
+ * deadlock the whole metrics system.
+ */
+ public StorageLocationReport[] getStorageReportSnapshot() {
+ // No lock is held, so the map sizes can change concurrently; collect into
a
+ // list instead of indexing into a pre-sized array.
+ List<StorageLocationReport> reports = new ArrayList<>(volumeMap.size() +
failedVolumeMap.size());
Review Comment:
done
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