why call runtime_doSpin after setting awoke =true

chenniannian · January 30, 2022, 3:40pm

golang/go/blob/897b3da2e079b9b940b309747305a5379fffa6ec/src/sync/mutex.go#L121

    
      
          	awoke := false
          	iter := 0
          	old := m.state
          	for {
          		// Don't spin in starvation mode, ownership is handed off to waiters
          		// so we won't be able to acquire the mutex anyway.
          		if old&(mutexLocked|mutexStarving) == mutexLocked && runtime_canSpin(iter) {
          			// Active spinning makes sense.
          			// Try to set mutexWoken flag to inform Unlock
          			// to not wake other blocked goroutines.
          			if !awoke && old&mutexWoken == 0 && old>>mutexWaiterShift != 0 &&
          				atomic.CompareAndSwapInt32(&m.state, old, old|mutexWoken) {
          				awoke = true
          			}
          			runtime_doSpin()
          			iter++
          			old = m.state
          			continue
          		}
          		new := old
          		// Don't try to acquire starving mutex, new arriving goroutines must queue.

According to the review, spinning is to set mutewoken.
But why it may call runtime_doSpin after setting awoke =true？

system · April 30, 2022, 3:41pm

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