8134930: Defer stack trace walking of NashornException for extracting line number and file name

Reviewed-by: hannesw, sundar

nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/api/scripting/NashornException.java

@@ -51,6 +51,8 @@ public abstract class NashornException extends RuntimeException {
     private String fileName;
     // script line number
     private int line;
+    // are the line and fileName unknown?
+    private boolean lineAndFileNameUnknown;
     // script column number
     private int column;
     // underlying ECMA error object - lazily initialized
@@ -92,27 +94,10 @@ public abstract class NashornException extends RuntimeException {
      */
     protected NashornException(final String msg, final Throwable cause) {
         super(msg, cause == null ? null : cause);
-        // This is not so pretty - but it gets the job done. Note that the stack
-        // trace has been already filled by "fillInStackTrace" call from
-        // Throwable
-        // constructor and so we don't pay additional cost for it.
-
         // Hard luck - no column number info
         this.column = -1;
-
-        // Find the first JavaScript frame by walking and set file, line from it
-        // Usually, we should be able to find it in just few frames depth.
-        for (final StackTraceElement ste : getStackTrace()) {
-            if (ECMAErrors.isScriptFrame(ste)) {
-                // Whatever here is compiled from JavaScript code
-                this.fileName = ste.getFileName();
-                this.line = ste.getLineNumber();
-                return;
-            }
-        }
-
-        this.fileName = null;
-        this.line = 0;
+        // We can retrieve the line number and file name from the stack trace if needed
+        this.lineAndFileNameUnknown = true;
     }
 
     /**
@@ -121,6 +106,7 @@ public abstract class NashornException extends RuntimeException {
      * @return the file name
      */
     public final String getFileName() {
+        ensureLineAndFileName();
         return fileName;
     }
 
@@ -131,6 +117,7 @@ public abstract class NashornException extends RuntimeException {
      */
     public final void setFileName(final String fileName) {
         this.fileName = fileName;
+        lineAndFileNameUnknown = false;
     }
 
     /**
@@ -139,6 +126,7 @@ public abstract class NashornException extends RuntimeException {
      * @return the line number
      */
     public final int getLineNumber() {
+        ensureLineAndFileName();
         return line;
     }
 
@@ -148,6 +136,7 @@ public abstract class NashornException extends RuntimeException {
      * @param line the line number
      */
     public final void setLineNumber(final int line) {
+        lineAndFileNameUnknown = false;
         this.line = line;
     }
 
@@ -274,4 +263,19 @@ public abstract class NashornException extends RuntimeException {
     public void setEcmaError(final Object ecmaError) {
         this.ecmaError = ecmaError;
     }
+
+    private void ensureLineAndFileName() {
+        if (lineAndFileNameUnknown) {
+            for (final StackTraceElement ste : getStackTrace()) {
+                if (ECMAErrors.isScriptFrame(ste)) {
+                    // Whatever here is compiled from JavaScript code
+                    fileName = ste.getFileName();
+                    line = ste.getLineNumber();
+                    return;
+                }
+            }
+
+            lineAndFileNameUnknown = false;
+        }
+    }
 }