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Re: Synchronization of the constructor

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On Aug 13, 8:13 am, markspace <-@.> wrote:
> On 8/13/2011 6:36 AM, Eric Sosman wrote:
>
> > On 8/13/2011 5:58 AM, MaciekL wrote:
> >> Hi,
>
> >> I have a doubt because Java disables synchronization of the constructor
> >> by default.
>
> > The constructor can be synchronized,
>
> It really can't.  Recall that the compiler will insert a call to a super
> constructor if the first statement doesn't have a such a call or a call
> to another class constructor.  Consider this:
>
> public class SomeClass {
>    public SomeClass() {
>      synchronized( SomeClass.class ) {
>        ...
>      }
>    }
> ...
>
> What you get is this:
>
> public class SomeClass {
>    public SomeClass() {
>      super();
>      synchronized( SomeClass.class ) {
>        ...
>      }
>    }
> ...
>
> And thus you see that some writes in the construction occur outside of
> the synchronized block, a classic case of incorrectly written
> synchronization.
>
> The closest Java gets to a synchronized constructor is immutable objects
> made with final fields.
>
> public class Immutable {
>    private final SomeObject o;
>    public Immutable() {
>      o = new SomeObject();
>    }
> ...
>
> This is thread safe, and immutable, because the fields written are
> declared "final."  Java takes special processing at the end of the
> constructor to synchronize all final fields, and any writes made to
> objects accessible via those final fields, with all other threads in the
> system.  So now this Immutable class can be used safely by any thread in
> the system.

Doesn't that depend on how Immutable SomeObject is and how Immutable's
immutability relates to it?
Also, other standard caveats apply (e.g. Immutable should be declared
final).

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Synchronization of the constructor MaciekL <__nospam__maclab@o2.pl> - 2011-08-13 11:58 +0200
  Re: Synchronization of the constructor Robert Klemme <shortcutter@googlemail.com> - 2011-08-13 12:17 +0200
    Re: Synchronization of the constructor "Qu0ll" <Qu0llSixFour@gmail.com> - 2011-08-13 21:36 +1000
      Re: Synchronization of the constructor Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-08-13 09:30 -0300
    [OT] Natural language. Was: Re: Synchronization of the constructor Patricia Shanahan <pats@acm.org> - 2011-08-13 07:10 -0700
  Re: Synchronization of the constructor Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-08-13 09:36 -0400
    Re: Synchronization of the constructor markspace <-@.> - 2011-08-13 08:13 -0700
      Re: Synchronization of the constructor Lew <lewbloch@gmail.com> - 2011-08-13 09:23 -0700
        Re: Synchronization of the constructor Patricia Shanahan <pats@acm.org> - 2011-08-13 10:04 -0700
          Re: Synchronization of the constructor Lew <lewbloch@gmail.com> - 2011-08-13 21:29 -0700
            Re: Synchronization of the constructor kedar mhaswade <kedar.mhaswade@gmail.com> - 2011-08-13 23:16 -0700
            Re: Synchronization of the constructor "Qu0ll" <Qu0llSixFour@gmail.com> - 2011-08-15 14:24 +1000
              Re: Synchronization of the constructor Lew <lewbloch@gmail.com> - 2011-08-14 23:03 -0700
      Re: Synchronization of the constructor kedar mhaswade <kedar.mhaswade@gmail.com> - 2011-08-13 23:12 -0700
        Re: Synchronization of the constructor markspace <-@.> - 2011-08-14 07:42 -0700
          Re: Synchronization of the constructor markspace <-@.> - 2011-08-14 07:51 -0700
            Re: Synchronization of the constructor Lew <lewbloch@gmail.com> - 2011-08-14 09:10 -0700
              Re: Synchronization of the constructor markspace <-@.> - 2011-08-14 11:28 -0700

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