CODEWITHSUNDEEP
multithreading
Ares
Ares

Reputation: 1461

Multi thread lock requirements

I had this as an interview question a while back, but I wasn't sure of the answer.

If you calculate c = c+1 with 100 threads, do you need a lock?

Upvotes: 1

Views: 178

Answers (2)

Malt
Malt

Reputation: 30285

Yes. The reason is that the statement c = c + 1 is actually (about) three low level statements:

1. read c from the memory
2. increment c by one
3. store c back to the memory

If two threads execute (1), they will both increment c to the same value and store it. So instead of being incremented twice, c will be incremented only once.

Upvotes: 1

usr
usr

Reputation: 171178

Yes, in pretty much every programming language that supports concurrency.

Upvotes: 0

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