Fix "Zeno’s paradox" like logic of the progress calculation.

Author: Dmytro Ukhlov

core/src/main/java/jenkins/widgets/RunListProgressiveRendering.java

@@ -24,6 +24,7 @@
 
 package jenkins.widgets;
 
+import com.google.common.collect.Iterables;
 import hudson.model.Run;
 import hudson.util.RunList;
 import java.util.ArrayList;
@@ -46,7 +47,9 @@ public abstract class RunListProgressiveRendering extends ProgressiveRendering {
      * The first increment will be sized as if this many runs will be in the total,
      * but then like Zeno’s paradox we will never seem to finish until we actually do.
      */
-    private static final double MAX_LIKELY_RUNS = 20;
+    private static final double MAX_LIKELY_RUNS = 20; // if (MAX_LIKELY_RUNS / 2) runs are processed, progress is 0.5
+    private static final int RUN_LIMIT = 1000; // Limit is need because UI doesn't have a pagination
+
     private final List<JSONObject> results = new ArrayList<>();
     private Iterable<? extends Run<?, ?>> builds;
 
@@ -56,8 +59,8 @@ public void setBuilds(Iterable<? extends Run<?, ?>> builds) {
     }
 
     @Override protected void compute() throws Exception {
-        double decay = 1;
-        for (Run<?, ?> build : builds) {
+        int processed = 0;
+        for (Run<?, ?> build : Iterables.limit(builds, RUN_LIMIT)) {
             if (canceled()) {
                 return;
             }
@@ -66,8 +69,8 @@ public void setBuilds(Iterable<? extends Run<?, ?>> builds) {
             synchronized (this) {
                 results.add(element);
             }
-            decay *= 1 - 1 / MAX_LIKELY_RUNS;
-            progress(1 - decay);
+            processed++;
+            progress(processed / (processed + MAX_LIKELY_RUNS / 2.0));
         }
     }