Groups > comp.lang.java.programmer > #30928

Re: a simple multi-thread question

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From	Robbie Brown <rob@example.com>
Newsgroups	comp.lang.java.programmer
Subject	Re: a simple multi-thread question
Date	Mon, 26 Jan 2015 19:51:10 +0000
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On 26/01/15 18:27, Arne Vajhøj wrote:
> On 1/26/2015 1:05 PM, Robbie Brown wrote:
>> On 26/01/15 15:55, Eric Sosman wrote:
>>> On 1/26/2015 10:40 AM, John wrote:
>>>>
>>>> I am amazed at what I saw:
>>>>
>>>> synchronized private void print()
>>>> {
>>>>       System.out.println("printing A");
>>>>       System.out.println("printing B");
>>>>       System.out.println("printing C");
>>>> }
>>>> [... he gets interleaved output ...]
>>>
>>>      Each Java object has its own lock ("monitor"), independent of the
>>> locks belonging to other Java objects.  When you call a synchronized
>>> instance method, Java acquires the lock of the "this" object before
>>> proceeding, and releases it when the method finishes.  If there are
>>> several object instances floating around, there are several "this"
>>> and several independent locks.
>>>
>>>> I thought the method is atomic.
>>>
>>>      No.  Synchronization is not about methods (or code blocks), but
>>> about objects: You lock the *object*, not a method.
>>
>> Are you sure?
>>
>> If you have a class with two methods and one (or more) of them is
>> synchronized and one (or more) isn't then a thread can obtain the lock
>> on an instance of that class which locks out all other threads from the
>> synchronized methods but the non synchronized methods of that instance
>> are still available to other threads.
>>
>> At least that's how I remember it.
>
> I think that is what Eric is saying.

Really?

"No.  Synchronization is not about methods (or code blocks), but
about objects: You lock the *object*, not a method"

seems pretty clear to me. 'still, I'm sure you know best.


-- 
Not floundering ... just fishing

Thread

a simple multi-thread question John <xsli2@yahoo.com> - 2015-01-26 07:40 -0800
  Re: a simple multi-thread question Arne Vajhøj <arne@vajhoej.dk> - 2015-01-26 10:53 -0500
  Re: a simple multi-thread question Robert Klemme <shortcutter@googlemail.com> - 2015-01-26 07:54 -0800
  Re: a simple multi-thread question Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-01-26 10:55 -0500
    Re: a simple multi-thread question Robbie Brown <rob@example.com> - 2015-01-26 18:05 +0000
      Re: a simple multi-thread question Robbie Brown <rob@example.com> - 2015-01-26 18:08 +0000
        Re: a simple multi-thread question Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-01-26 17:19 -0500
      Re: a simple multi-thread question Arne Vajhøj <arne@vajhoej.dk> - 2015-01-26 13:27 -0500
        Re: a simple multi-thread question Robbie Brown <rob@example.com> - 2015-01-26 19:51 +0000
  Re: a simple multi-thread question Jukka Lahtinen <jtfjdehf@hotmail.com.invalid> - 2015-01-28 21:55 +0200

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