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Ranch Hand
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Hey guys, I was doing an mock from ExamLab and this question appeared:


It says that the answer is: 000000

Can anyone explain to me what happened?

Thanks
 
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Matheus Souza wrote:It says that the answer is: 000000


That is correct.

Matheus Souza wrote:Can anyone explain to me what happened?


What exactly didn't you understand? Is it why 6 numbers are printed? Or is it why 0 is printed every time? Or both?

6 numbers were printed because, after execution of 1 thread (just one thread. not first or second - because we cannot guarantee which thread will execute first), length of s would be 1. After execution of 2 threads, length of s would be 2 and after execution of 3 threads length would be 3. Further, we are printing s for 3 times, hence, we get 1+2+3=6 numbers. This modification of s is thread safe because of synchronization(line 20)

Now, what happens to those numbers we passed during object creation (2,1 and 0)? Well, x is volatile. So, every time, a thread would refer copy from main memory (and not thread's local memory), so it will take 0 every time.

I hope this helps.
 
Greenhorn
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IMO x variable is static so it's value the same for all objects. The last constructor set x to 0 and then started all threads, thats why result 000000.
 
Anayonkar Shivalkar
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rimantas grebliunas wrote:IMO x variable is static so it's value the same for all objects. The last constructor set x to 0 and then started all threads, thats why result 000000.


How did I miss this?

Thanks rimantas grebliunas for the correction.
 
Matheus Souza
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Anayonkar Shivalkar wrote:

rimantas grebliunas wrote:IMO x variable is static so it's value the same for all objects. The last constructor set x to 0 and then started all threads, thats why result 000000.


How did I miss this?

Thanks rimantas grebliunas for the correction.



Thanks you guys, I got it. This is a very tricky question, insn't it? =]
 
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