HBASE-25995 Change the method name for DoubleArrayCost.setCosts (#3381)

Signed-off-by: Yulin Niu <[email protected]>

Author: Apache9

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/DoubleArrayCost.java

@@ -43,7 +43,16 @@ void prepare(int length) {
     }
   }
 
-  void setCosts(Consumer<double[]> consumer) {
+  /**
+   * We do not want to introduce a getCosts method to let upper layer get the cost array directly,
+   * so here we introduce this method to take a {@link Consumer} as parameter, where we will pass
+   * the actual cost array in, so you can change the element of the cost array in the
+   * {@link Consumer} implementation.
+   * <p/>
+   * Usually, in prepare method, you need to fill all the elements of the cost array, while in
+   * regionMoved method, you just need to update the element for the effect region servers.
+   */
+  void applyCostsChange(Consumer<double[]> consumer) {
     consumer.accept(costs);
     costsChanged = true;
   }

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/StochasticLoadBalancer.java

@@ -864,7 +864,7 @@ static class RegionCountSkewCostFunction extends CostFunction {
     void init(Cluster cluster) {
       super.init(cluster);
       cost.prepare(cluster.numServers);
-      cost.setCosts(costs -> {
+      cost.applyCostsChange(costs -> {
         for (int i = 0; i < cluster.numServers; i++) {
           costs[i] = cluster.regionsPerServer[i].length;
         }
@@ -886,7 +886,7 @@ protected double cost() {
 
     @Override
     protected void regionMoved(int region, int oldServer, int newServer) {
-      cost.setCosts(costs -> {
+      cost.applyCostsChange(costs -> {
         costs[oldServer] = cluster.regionsPerServer[oldServer].length;
         costs[newServer] = cluster.regionsPerServer[newServer].length;
       });
@@ -928,7 +928,7 @@ void init(Cluster cluster) {
         return;
       }
       cost.prepare(cluster.numServers);
-      cost.setCosts(costs -> {
+      cost.applyCostsChange(costs -> {
         for (int i = 0; i < costs.length; i++) {
           costs[i] = computeCostForRegionServer(i);
         }
@@ -942,7 +942,7 @@ boolean isNeeded() {
 
     @Override
     protected void regionMoved(int region, int oldServer, int newServer) {
-      cost.setCosts(costs -> {
+      cost.applyCostsChange(costs -> {
         costs[oldServer] = computeCostForRegionServer(oldServer);
         costs[newServer] = computeCostForRegionServer(newServer);
       });
@@ -1110,7 +1110,7 @@ private double computeCostForRegionServer(int regionServerIndex) {
     void init(Cluster cluster) {
       super.init(cluster);
       cost.prepare(cluster.numServers);
-      cost.setCosts(costs -> {
+      cost.applyCostsChange(costs -> {
         for (int i = 0; i < costs.length; i++) {
           costs[i] = computeCostForRegionServer(i);
         }
@@ -1120,7 +1120,7 @@ void init(Cluster cluster) {
     @Override
     protected void regionMoved(int region, int oldServer, int newServer) {
       // recompute the stat for the given two region servers
-      cost.setCosts(costs -> {
+      cost.applyCostsChange(costs -> {
         costs[oldServer] = computeCostForRegionServer(oldServer);
         costs[newServer] = computeCostForRegionServer(newServer);
       });

hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestDoubleArrayCost.java

@@ -38,15 +38,15 @@ public void testComputeCost() {
     DoubleArrayCost cost = new DoubleArrayCost();
 
     cost.prepare(100);
-    cost.setCosts(costs -> {
+    cost.applyCostsChange(costs -> {
       for (int i = 0; i < 100; i++) {
         costs[i] = 10;
       }
     });
     assertEquals(0, cost.cost(), 0.01);
 
     cost.prepare(101);
-    cost.setCosts(costs -> {
+    cost.applyCostsChange(costs -> {
       for (int i = 0; i < 100; i++) {
         costs[i] = 0;
       }
@@ -55,7 +55,7 @@ public void testComputeCost() {
     assertEquals(1, cost.cost(), 0.01);
 
     cost.prepare(200);
-    cost.setCosts(costs -> {
+    cost.applyCostsChange(costs -> {
       for (int i = 0; i < 100; i++) {
         costs[i] = 0;
         costs[i + 100] = 100;