Questions on `Mutex.kt` ``` internal class MutexI...

# coroutines

[dsgryazin]

Questions on Mutex.kt

internal class MutexImpl(locked: Boolean) : Mutex, SelectClause2<Any?, Mutex> {
    // State is: Empty | LockedQueue | OpDescriptor
    // shared objects while we have no waiters
    private val _state = atomic<Any?>(if (locked) EmptyLocked else EmptyUnlocked)

    // resumeNext is: RESUME_QUIESCENT | RESUME_ACTIVE | ResumeReq
    private val _resumeNext = atomic<Any>(RESUME_QUIESCENT)

    public override val isLocked: Boolean get() {
        _state.loop { state ->
            when (state) {
                is Empty -> return state.locked !== UNLOCKED
                is LockedQueue -> return true
                is OpDescriptor -> state.perform(this) // help
                else -> error("Illegal state $state")
            }
        }
    }

1. Please, explain, what is meant by each of Empty | LockedQueue | OpDescriptor?
2. What is for resumeNext is: RESUME_QUIESCENT | RESUME_ACTIVE | ResumeReq?
3. What means the `help`comment in is OpDescriptor -> state.perform(this) // help? 😅

[elizarov]

1 & 2 explain what possible types can be stored in the corresponding variable with declared type of Any?

[elizarov]

3. Read docs in OpDescriptor class and AtomicOp in the same file.

[dsgryazin]

Well, ok, gonna study the paper

[dsgryazin]

I wanted to understand how the mutex is done, that is what questions 1&2 are about. Can not understand what OpDescriptor is for. Is there a popular preparation of Mutex?

[elizarov]

You don’t have to understand OpDescriptor for that. It is only use when Mutex is a part of select, which you can ignore at first. Assume that OpDescriptor never happens there