From 2abec5dd6b714f1b693a632b534f9faf95ebe237 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Genevi=C3=A8ve=20Bastien?= <gbastien+lttng@versatic.net>
Date: Tue, 21 Feb 2017 14:35:45 -0500
Subject: [PATCH] datastore: Keep a snapshot of the latest branch
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This avoids making immutable copies of the same branch over and over.

Also use the latest branch directly in the node insertion instead of
the getter.

This change alone removes all performance impact of the datastore
when building.

Change-Id: If85ae9bded364cfd6f1243416d025df6307cf909
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/91755
Reviewed-by: Hudson CI
Reviewed-by: Loic Prieur-Drevon <loic.prieur.drevon@ericsson.com>
---
 .../core/historytree/AbstractHistoryTree.java    | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/statesystem/org.eclipse.tracecompass.datastore.core/src/org/eclipse/tracecompass/internal/provisional/datastore/core/historytree/AbstractHistoryTree.java b/statesystem/org.eclipse.tracecompass.datastore.core/src/org/eclipse/tracecompass/internal/provisional/datastore/core/historytree/AbstractHistoryTree.java
index 85df36becf..b61152059e 100644
--- a/statesystem/org.eclipse.tracecompass.datastore.core/src/org/eclipse/tracecompass/internal/provisional/datastore/core/historytree/AbstractHistoryTree.java
+++ b/statesystem/org.eclipse.tracecompass.datastore.core/src/org/eclipse/tracecompass/internal/provisional/datastore/core/historytree/AbstractHistoryTree.java
@@ -118,6 +118,8 @@ public abstract class AbstractHistoryTree<E extends IHTInterval, N extends HTNod
     /* Lock used to protect the accesses to the HT_IO object */
     private final ReentrantReadWriteLock fRwl = new ReentrantReadWriteLock(false);
 
+    private transient @Nullable List<N> fLatestBranchSnapshot = null;
+
     /**
      * Create a new State History from scratch, specifying all configuration
      * parameters.
@@ -364,8 +366,15 @@ public abstract class AbstractHistoryTree<E extends IHTInterval, N extends HTNod
      * @return The immutable latest branch
      */
     @VisibleForTesting
-    List<N> getLatestBranch() {
-        return ImmutableList.copyOf(fLatestBranch);
+    final List<N> getLatestBranch() {
+        List<N> latestBranchSnapshot = fLatestBranchSnapshot;
+        if (latestBranchSnapshot == null) {
+            synchronized (fLatestBranch) {
+                latestBranchSnapshot = ImmutableList.copyOf(fLatestBranch);
+                fLatestBranchSnapshot = latestBranchSnapshot;
+            }
+        }
+        return latestBranchSnapshot;
     }
 
     /**
@@ -634,7 +643,7 @@ public abstract class AbstractHistoryTree<E extends IHTInterval, N extends HTNod
      *            insertion
      */
     protected final void tryInsertAtNode(E interval, int depth) {
-        N targetNode = getLatestBranch().get(depth);
+        N targetNode = fLatestBranch.get(depth);
         informInsertingAtDepth(depth);
 
         /* Verify if there is enough room in this node to store this interval */
@@ -710,6 +719,7 @@ public abstract class AbstractHistoryTree<E extends IHTInterval, N extends HTNod
     private final void addSiblingNode(int depth, long newNodeStartTime) {
         synchronized (fLatestBranch) {
             final long splitTime = fTreeEnd;
+            fLatestBranchSnapshot = null;
 
             if (depth >= fLatestBranch.size()) {
                 /*
-- 
2.34.1