Groups > comp.lang.java.programmer > #7081

Re: Synchronization of the constructor

From	markspace <-@.>
Newsgroups	comp.lang.java.programmer
Subject	Re: Synchronization of the constructor
Date	2011-08-13 08:13 -0700
Organization	A noiseless patient Spider
Message-ID	<j264b6$3u5$1@dont-email.me> (permalink)
References	<j25hro$cjf$1@news.onet.pl> <j25uri$vm$1@dont-email.me>

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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.

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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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