Re: Is 'new' operator thread-safe?

Patricia Shanahan <>
Tue, 05 Dec 2006 16:39:47 GMT
xie bo wrote:

    Reference? Oh, I dunno, but I'd be willing to
bet you'll find something in the JLS.

I checked JLS and following is citation.
Section 17.5 Final Field Semantics
An object is considered to be completely initialized when its
constructor finishes. A thread that can only see a reference to an
object after that object has been completely initialized is guaranteed
to see the correctly initialized values for that object's final fields.

Is the above reference mean '"new" operator is thread-safe for Java'?


Not necessarily. It depends, as Eric pointed out, on what the
constructor does:

public class SynchTest {
   static int count1 = 0;

   static int count2 = 0;

   public static void main(String[] args) {
     Runnable myRun = new Runnable() {
       public void run() {
           new SynchTest();

     Thread[] allThreads = new Thread[10];
     for(int i=0; i<allThreads.length; i++){
       allThreads[i] = new Thread(myRun);
     for(Thread t : allThreads){
     for(Thread t : allThreads){
       try {
       } catch (InterruptedException e) {
       "Actual=%d count1=%d count2=%d%n",
       allThreads.length, count1, count2

   public SynchTest() {

   private void goodIncrement() {
     synchronized (this.getClass()) {

   private void badIncrement() {
     int x = count2;
     try {
     } catch (InterruptedException e) {
     count2 = x;

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