Gargi-jais11 commented on code in PR #10109:
URL: https://github.com/apache/ozone/pull/10109#discussion_r3233389538
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hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/impl/ContainerSet.java:
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@@ -279,6 +285,49 @@ public Container<?> getContainer(long containerId) {
return containerMap.get(containerId);
}
+ /**
+ * Returns the max retry for a container map swap while acquiring container
lock.
+ * @return max retry count
+ */
+ public static int maxContainerMapSwapRetries() {
+ return MAX_CONTAINER_MAP_SWAP_RETRIES;
+ }
+
+ /**
+ * Locks the container mapped to {@code containerId} for write, and verifies
that the instance locked is still
+ * the one stored in this set. If the mapping is swapped or the container no
longer exists, unlocks and retries up to
+ * {@link #maxContainerMapSwapRetries()} times, then returns {@code null}.
+ *
+ * @return the locked container, or {@code null} if none mapped, or mapping
could not be stabilized
+ */
+ @Nullable
+ public Container<?> acquireContainerLock(long containerId) {
+ for (int retry = 0; retry < MAX_CONTAINER_MAP_SWAP_RETRIES; retry++) {
+ Container<?> candidate = getContainer(containerId);
+ if (candidate == null) {
+ LOG.info("Container {} no longer present in ContainerSet, skipping.",
containerId);
+ return null;
+ }
+ candidate.writeLock();
+ Container<?> current = getContainer(containerId);
+ if (current == null) {
+ candidate.writeUnlock();
+ LOG.info("Container {} no longer exists in ContainerSet while
acquiring lock.", containerId);
+ return null;
+ }
+ if (current != candidate) {
+ candidate.writeUnlock();
+ if (LOG.isDebugEnabled()) {
+ LOG.debug("Container {} mapping changed during lock acquisition
(attempt {}); retrying.",
Review Comment:
@sodonnel but for now there is only diskbalancer which will swap container
in in-memory. for one diskbalancer task it operates only one time on that
container. It's very rarest case that the same container will be eligible to
move to other disk again but that too will happen in next iteration of balancer
and since we already writeLock wound be working on current then diskbalancer
won't able to acquire readLock again on same container.
considering the above I don't think there is any gap left for this. Please
correct me if I am wrong.
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