CODEWITHSUNDEEP
javamultithreadingsynchronizationthread-safety
Bravo
Bravo

Reputation: 9029

is CAS (compare and SWAP ) work perfectly fine?

Have a small doubt on the correctness of "compare and swap " in java , because

i am still thinking this CAS also have a chance to lost the values , for example

lets a shared resource S , with the value 5

and threads T1 and T2 , want to update the values with the new values 6 and 7 respectively .

1 . T1 compare the value with 5 and found same 2. T2 compare the value with 5 and found same 3 . T2 set the values to 7 4. T1 set the value to 6

so now here the value set by the T2 lost as the T1 reads the old current value which is 5 at that time.

can anyone please explain on this please

Upvotes: 0

Views: 87

Answers (1)

Kayaman
Kayaman

Reputation: 73528

What you described can't happen, due to the atomicity of CAS.

It's not "Compare-Then-Swap", it's "Compare-And-Swap". There's no separate phase for compare and another phase for swap. That's the whole beauty of it.

Upvotes: 2

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