GH-609 cache value of static field java.lang.StringUTF16.HI_BYTE_SHIFT and java.lang.StringUTF16.LO_BYTE_SHIFT

Author: thurka

visualvm/libs.profiler/lib.profiler.heap/src/org/graalvm/visualvm/lib/jfluid/heap/HprofProxy.java

@@ -25,7 +25,9 @@
 
 package org.graalvm.visualvm.lib.jfluid.heap;
 
+import java.util.Map;
 import java.util.Properties;
+import java.util.WeakHashMap;
 
 
 /**
@@ -143,16 +145,24 @@ private static char[] getChars(PrimitiveArrayDump chars, Byte coder, int offset,
                 return "*unknown coder*".toCharArray();
         }
     }
-    
+
+    private static final Map<Heap,int[]> CACHE = new WeakHashMap<>();
+
     private static int[] getStringUTF16ShiftBytes(Heap heap) {
-        JavaClass utf16Class = heap.getJavaClassByName("java.lang.StringUTF16");                  // NOI18N
-        Integer HI_BYTE_SHIFT = (Integer) utf16Class.getValueOfStaticField("HI_BYTE_SHIFT");      // NOI18N
-        Integer LO_BYTE_SHIFT = (Integer) utf16Class.getValueOfStaticField("LO_BYTE_SHIFT");      // NOI18N
+        int[] shiftBytes = CACHE.get(heap);
 
-        if (HI_BYTE_SHIFT != null && LO_BYTE_SHIFT != null) {
-            return new int[] {HI_BYTE_SHIFT.intValue(),LO_BYTE_SHIFT.intValue()};
+        if (shiftBytes == null) {
+            JavaClass utf16Class = heap.getJavaClassByName("java.lang.StringUTF16");                  // NOI18N
+            Integer HI_BYTE_SHIFT = (Integer) utf16Class.getValueOfStaticField("HI_BYTE_SHIFT");      // NOI18N
+            Integer LO_BYTE_SHIFT = (Integer) utf16Class.getValueOfStaticField("LO_BYTE_SHIFT");      // NOI18N
+
+            if (HI_BYTE_SHIFT != null && LO_BYTE_SHIFT != null) {
+                shiftBytes = new int[] {HI_BYTE_SHIFT.intValue(), LO_BYTE_SHIFT.intValue()};
+            }
+            // use default
+            shiftBytes = new int[] {0,8};
+            CACHE.put(heap, shiftBytes);
         }
-        // use default
-        return new int[] {0,8};
+        return shiftBytes;
     }
 }

visualvm/libs.profiler/profiler.heapwalker/src/org/graalvm/visualvm/lib/profiler/heapwalk/details/api/StringDecoder.java

@@ -25,6 +25,8 @@
 package org.graalvm.visualvm.lib.profiler.heapwalk.details.api;
 
 import java.util.List;
+import java.util.Map;
+import java.util.WeakHashMap;
 import org.graalvm.visualvm.lib.jfluid.heap.Heap;
 import org.graalvm.visualvm.lib.jfluid.heap.JavaClass;
 
@@ -34,6 +36,8 @@
  */
 public final class StringDecoder {
 
+    private static final Map<Heap,int[]> CACHE = new WeakHashMap<>();
+
     private final byte coder;
     private final List<String> values;
     private int HI_BYTE_SHIFT;
@@ -43,18 +47,23 @@ public StringDecoder(Heap heap, byte c, List<String> val) {
         coder = c;
         values = val;
         if (coder == 1) {
-            JavaClass utf16Class = heap.getJavaClassByName("java.lang.StringUTF16"); // NOI18N
-            Integer hiShift = (Integer) utf16Class.getValueOfStaticField("HI_BYTE_SHIFT"); // NOI18N
-            Integer loShift = (Integer) utf16Class.getValueOfStaticField("LO_BYTE_SHIFT"); // NOI18N
+            int[] shiftBytes = CACHE.get(heap);
+
+            if (shiftBytes == null) {
+                JavaClass utf16Class = heap.getJavaClassByName("java.lang.StringUTF16"); // NOI18N
+                Integer hiShift = (Integer) utf16Class.getValueOfStaticField("HI_BYTE_SHIFT"); // NOI18N
+                Integer loShift = (Integer) utf16Class.getValueOfStaticField("LO_BYTE_SHIFT"); // NOI18N
 
-            if (hiShift != null && loShift != null) {
-                HI_BYTE_SHIFT = hiShift.intValue();
-                LO_BYTE_SHIFT = loShift.intValue();
-            } else {
-                // use default
-                HI_BYTE_SHIFT = 0;
-                LO_BYTE_SHIFT = 8;
+                if (hiShift != null && loShift != null) {
+                    shiftBytes = new int[] {hiShift.intValue(), loShift.intValue()};
+                } else {
+                    // use default
+                    shiftBytes = new int[] {0,8};
+                }
+                CACHE.put(heap, shiftBytes);
             }
+            HI_BYTE_SHIFT = shiftBytes[0];
+            LO_BYTE_SHIFT = shiftBytes[1];
         }
     }