Adds Helper#getUsedMBAfterGC.

Author: easbar

api/src/main/java/com/graphhopper/util/Helper.java

@@ -20,6 +20,8 @@
 import com.graphhopper.util.shapes.BBox;
 
 import java.io.*;
+import java.lang.management.GarbageCollectorMXBean;
+import java.lang.management.ManagementFactory;
 import java.nio.ByteBuffer;
 import java.nio.MappedByteBuffer;
 import java.nio.charset.Charset;
@@ -174,6 +176,29 @@ public static String getMemInfo() {
         return "totalMB:" + getTotalMB() + ", usedMB:" + getUsedMB();
     }
 
+    public static int getUsedMBAfterGC() {
+        long before = getTotalGcCount();
+        // trigger gc
+        System.gc();
+        while (getTotalGcCount() == before) {
+            // wait for the gc to have completed
+        }
+        long result = (ManagementFactory.getMemoryMXBean().getHeapMemoryUsage().getUsed() +
+                ManagementFactory.getMemoryMXBean().getNonHeapMemoryUsage().getUsed()) / (1024 * 1024);
+        return (int) result;
+    }
+
+    private static long getTotalGcCount() {
+        long sum = 0;
+        for (GarbageCollectorMXBean b : ManagementFactory.getGarbageCollectorMXBeans()) {
+            long count = b.getCollectionCount();
+            if (count != -1) {
+                sum += count;
+            }
+        }
+        return sum;
+    }
+
     public static int getSizeOfObjectRef(int factor) {
         // pointer to class, flags, lock
         return factor * (4 + 4 + 4);