[JENKINS-75586] Add configurable maximum concurrent indexing limit

src/main/java/jenkins/branch/MultiBranchProject.java

@@ -132,6 +132,13 @@
 
     private static /* not final */ boolean FIRE_SCM_SOURCE_BUILDS_AFTER_SAVE =
         SystemProperties.getBoolean(MultiBranchProject.class.getName() + ".fireSCMSourceBuildsAfterSave", true);
+
+    /**
+     * Maximum concurrent indexing.
+     * Can be configured via system property jenkins.branch.MultiBranchProject.maxConcurrentIndexing
+     */
+    private static final int MAX_CONCURRENT_INDEXING = 
+        SystemProperties.getInteger(MultiBranchProject.class.getName() + ".maxConcurrentIndexing", 5);
 
     /**
      * Our logger.
@@ -905,6 +912,15 @@
     public synchronized BranchIndexing<P, R> getIndexing() {
         return (BranchIndexing) getComputation();
     }
+
+    /**
+     * Returns the maximum concurrent indexing limit.
+     *
+     * @return the maximum concurrent indexing limit
+     */
+    public static int getMaxConcurrentIndexing() {
+        return MAX_CONCURRENT_INDEXING;
+    }
 
     /**
      * {@inheritDoc}
@@ -1082,6 +1098,35 @@
         }
         return super.isBuildable() && !sources.isEmpty();
     }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public hudson.model.queue.CauseOfBlockage getCauseOfBlockage() {
+        // Check if we've exceeded the maximum concurrent indexing limit
+        if (indexingCount() > MAX_CONCURRENT_INDEXING) {
+            return hudson.model.queue.CauseOfBlockage.fromMessage(
+                Messages._MultiBranchProject_MaxConcurrentIndexing(MAX_CONCURRENT_INDEXING)
+            );
+        }
+        return super.getCauseOfBlockage();
+    }
+
+    /**
+     * Count the number of multibranch projects currently indexing.
+     * 
+     * @return the number of projects currently indexing
+     */
+    private static int indexingCount() {
+        int count = 0;
+        for (MultiBranchProject<?, ?> project : Jenkins.get().getAllItems(MultiBranchProject.class)) {
+            if (project.getComputation() != null && project.getComputation().isBuilding()) {
+                count++;
+            }
+        }
+        return count;
+    }
 
     /**
      * {@inheritDoc}

src/main/resources/jenkins/branch/Messages.properties

@@ -48,6 +48,7 @@ RateLimitBranchProperty.duration.month=Month
 RateLimitBranchProperty.duration.year=Year
 MultiBranchProject.BranchIndexing.displayName=Scan {0}
 MultiBranchProject.CopyItemVeto.reason=Copying branch projects outside of their multi-branch container is not supported.
+MultiBranchProject.MaxConcurrentIndexing=Already indexing maximum number of projects (limit: {0})
 MultiBranchProjectDisplayNamingTrait.DisplayName=Job display name with fallback to name
 MultiBranchProjectDisplayNamingTrait.Raw=Simple name only
 MultiBranchProjectDisplayNamingTrait.RawAndDisplayName=Name and, if available, display name