From d3f7c0196ecf58b78574d8b80e1844ecb4e223d6 Mon Sep 17 00:00:00 2001
From: Tuukka Lehtonen <tuukka.lehtonen@semantum.fi>
Date: Fri, 5 Jun 2020 01:33:16 +0300
Subject: [PATCH] Avoid useless reallocation of empty TreeMaps and map
 iterators

The problem was that when the database is doing work, MainProgram.run
runs in pretty much busy loop mode and previously it was always
allocating a new TreeMap on each round and also calling Map.entrySet()
to get construct iterators for empty TreeMaps which eventually
accumulates up to somewhat signinificant amount of memory allocated.

Possibly an even more efficient way would be to have the Map be a closed
hashing hashmap instead and then sorting the data for iteration
separately.

gitlab #548

Change-Id: Ib2208dc35b270c9d682362d45f24f1fe01bb8969
---
 .../src/org/simantics/acorn/MainProgram.java          | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/bundles/org.simantics.acorn/src/org/simantics/acorn/MainProgram.java b/bundles/org.simantics.acorn/src/org/simantics/acorn/MainProgram.java
index 1e4b5cbac..52be328eb 100644
--- a/bundles/org.simantics.acorn/src/org/simantics/acorn/MainProgram.java
+++ b/bundles/org.simantics.acorn/src/org/simantics/acorn/MainProgram.java
@@ -70,7 +70,7 @@ public class MainProgram implements Runnable, Closeable {
 		this.updateSchedules = new ArrayList[CLUSTER_THREADS];
 		for(int i=0;i<clusterUpdateThreads.length;i++) {
 			clusterUpdateThreads[i] = Executors.newSingleThreadExecutor(new ClusterThreadFactory("Cluster Updater " + (i+1), false));
-			updateSchedules[i] = new ArrayList<ClusterUpdateOperation>();
+			updateSchedules[i] = new ArrayList<>();
 		}
 	}
 
@@ -93,11 +93,13 @@ public class MainProgram implements Runnable, Closeable {
 
 		try {
 
+			TreeMap<ClusterUID, List<ClusterUpdateOperation>> updates = new TreeMap<>(clusterComparator);
+
 			main:
 			while(alive) {
 
-				TreeMap<ClusterUID, List<ClusterUpdateOperation>> updates = new TreeMap<ClusterUID, List<ClusterUpdateOperation>>(clusterComparator);
-
+				if (!updates.isEmpty())
+					updates.clear();
 				operationQueue.pumpUpdates(updates);
 
 				if(updates.isEmpty()) {
@@ -165,6 +167,9 @@ public class MainProgram implements Runnable, Closeable {
 		for(int i=0;i<CLUSTER_THREADS;i++)
 			updateSchedules[i].clear();
 
+		if (updates.isEmpty())
+			return;
+
 		final Semaphore s = new Semaphore(0);
 
 		for(Map.Entry<ClusterUID, List<ClusterUpdateOperation>> entry : updates.entrySet()) {
-- 
2.43.2