[GitHub] [lucene] mikemccand commented on a diff in pull request #11780: GH#11601: Add ability to compute reader states after refresh

[GitBox <gi...@apache.org>]

mikemccand commented on code in PR #11780:
URL: https://github.com/apache/lucene/pull/11780#discussion_r982553986


##########
lucene/core/src/java/org/apache/lucene/search/ReferenceManager.java:
##########
@@ -219,6 +219,36 @@ public final boolean maybeRefresh() throws IOException {
     return doTryRefresh;
   }
 
+  /** Compute some state of the reference using a parameter. */
+  @FunctionalInterface
+  public interface StateCalculator<R, G, P> {
+    R calculate(G current, P param);
+  }
+
+  /**
+   * If you need to compute something after the refresh, you can use this method instead of {@link
+   * #maybeRefresh()}.
+   *
+   * @throws IOException if refreshing the resource causes an {@link IOException}
+   */
+  public final <R, P> R maybeRefreshAndReturnState(
+      StateCalculator<R, G, P> refreshedStateCalculator, P param) throws IOException {
+    ensureOpen();
+
+    // Ensure only 1 thread does refresh at once; other threads just return immediately:
+    final boolean doTryRefresh = refreshLock.tryLock();
+    if (doTryRefresh) {
+      try {
+        doMaybeRefresh();
+        return refreshedStateCalculator.calculate(current, param);

Review Comment:
   Hmm why is it necessary to compute this state under lock?  Can't the caller just compute the state themselves when they get the refreshed reader?



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