Is it thread safy to modify a mutable variable for a mutableStateFlow in producer and consumer concurrently?

Question

Refer to following codes:

    @Test
    fun test() = runBlocking {
        val tag = testName.methodName
        var mutFlow = MutableStateFlow(mutableListOf<Int>())
        val imFlow = mutFlow.asStateFlow()

        Log.d(tag, "mutable value is ${imFlow.value}")
        val job = launch {
            imFlow.collect {
                Log.d(tag, "job1 collected value is $it @${System.identityHashCode(it)}")
                it.add(100)
            }
        }
        repeat (5) {
            val a = mutFlow.value
            a.add(it)
            mutFlow.value = a
            delay(1)
        }
        delay(10)
        Log.d(tag, "mutable value is ${imFlow.value}")
        job.cancelAndJoin()
    }

Two questions:

1. Is it thread safy to modify a mutable variable in producer and consumer concurrently?
2. Why consumer just got one collect callback?

This is the log:

D test: mutable value is []
D test: job1 collected value is [0] @153163998
D test: mutable value is [0, 100, 1, 2, 3, 4]