8349241: Fix the concurrent execution JVM crash of StringBuilder::append(int/long)

src/java.base/share/classes/java/lang/AbstractStringBuilder.java

@@ -241,11 +241,30 @@ public void ensureCapacity(int minimumCapacity) {
      */
     private void ensureCapacityInternal(int minimumCapacity) {
         // overflow-conscious code
-        int oldCapacity = value.length >> coder;
+        ensureCapacityInternal(minimumCapacity, coder);
+    }
+
+    /**
+     * For positive values of {@code minimumCapacity}, this method
+     * behaves like {@code ensureCapacity}, however it is never
+     * synchronized.
+     * If {@code minimumCapacity} is non positive due to numeric
+     * overflow, this method throws {@code OutOfMemoryError}.
+     *
+     * @param   minimumCapacity   the minimum desired capacity.
+     * @param   coder the coder to be used when calculating the capacity length.
+     * @return  Returns the value that ensures the capacity
+     */
+    private byte[] ensureCapacityInternal(int minimumCapacity, byte coder) {
+        // overflow-conscious code
+        byte[] val = this.value;
+        int oldCapacity = val.length >> coder;
         if (minimumCapacity - oldCapacity > 0) {
-            value = Arrays.copyOf(value,
-                    newCapacity(minimumCapacity) << coder);
+            val = Arrays.copyOf(val,
+                    newCapacity(minimumCapacity, val.length, coder) << coder);
+            this.value = val;
         }
+        return val;
     }
 
     /**
@@ -257,11 +276,12 @@ private void ensureCapacityInternal(int minimumCapacity) {
      * unless the given minimum capacity is greater than that.
      *
      * @param  minCapacity the desired minimum capacity
+     * @param  oldLength the raw length of the current value array, without being processed using coder.
+     * @param  coder the coder to be used when calculating the capacity length
      * @throws OutOfMemoryError if minCapacity is less than zero or
      *         greater than (Integer.MAX_VALUE >> coder)
      */
-    private int newCapacity(int minCapacity) {
-        int oldLength = value.length;
+    private static int newCapacity(int minCapacity, int oldLength, byte coder) {
         int newLength = minCapacity << coder;
         int growth = newLength - oldLength;
         int length = ArraysSupport.newLength(oldLength, growth, oldLength + (2 << coder));
@@ -838,8 +858,9 @@ public AbstractStringBuilder append(char c) {
     public AbstractStringBuilder append(int i) {
         int count = this.count;
         int spaceNeeded = count + DecimalDigits.stringSize(i);
-        ensureCapacityInternal(spaceNeeded);
-        if (isLatin1()) {
+        byte coder = this.coder;
+        byte[] value = ensureCapacityInternal(spaceNeeded, coder);
+        if (coder == LATIN1) {
             DecimalDigits.getCharsLatin1(i, spaceNeeded, value);
         } else {
             DecimalDigits.getCharsUTF16(i, spaceNeeded, value);
@@ -863,8 +884,9 @@ public AbstractStringBuilder append(int i) {
     public AbstractStringBuilder append(long l) {
         int count = this.count;
         int spaceNeeded = count + DecimalDigits.stringSize(l);
-        ensureCapacityInternal(spaceNeeded);
-        if (isLatin1()) {
+        byte coder = this.coder;
+        byte[] value = ensureCapacityInternal(spaceNeeded, coder);
+        if (coder == LATIN1) {
             DecimalDigits.getCharsLatin1(l, spaceNeeded, value);
         } else {
             DecimalDigits.getCharsUTF16(l, spaceNeeded, value);