202408281908

Tags : Concurrent Programming

TAS Lock

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TAS lock is an implementation of a lock that uses the read-modify-write instructions to work with hardware architecture that could otherwise reorder lock implementations and break them.

struct TAS{
	state : Atom<bool>
}
 
impl Lock for TAS {
  fn lock(self) {
    wait_while(state.get_and_set(true))
    // This lock will stop waiting only when 
    // another process sets the lock to false
  }
  fn unlock(self) {
    state.set(false)
  }
}

The correctness of the lock comes from the fact that the state if false iff there is no thread in the critical section, each time a threads wants to get into one, it sets the state to false until it exists CS at which point another thread can enter the critical section.

Expensive

The problem with TAS lock is that it repeatedly uses the get_and_set() functions which is extremely expensive. This problem is improved with TTAS Lock

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References