kotlin - 为什么 runBlocking 没有阻塞调用线程

Question

我想了解 kotlin 中的 runBlocking。

 println("before runBlocking ${Thread.currentThread().name}")

    runBlocking { // but this expression blocks the main thread
        delay(2000L) // non blocking
        println("inside runBlocking ${Thread.currentThread().name}")
        delay(2000L)
    }

    println("after runBlocking ${Thread.currentThread().name}")

输出

before runBlocking main
inside runBlocking main
after runBlocking main

Kotlin Says

1. runBlocking - Runs a new coroutine and blocks the current thread interruptibly until its completion
2. The main thread invoking runBlocking blocks until the coroutine inside runBlocking completes.

第 1 点:- 如果 runBlocking 阻止了 main上面例子中的线程。然后在 runBlocking 中我如何获得 main再次线程。

第 2 点:- 如果 Runs a new coroutine在上面的陈述中是真的，那么为什么它没有创建新的 coroutine里面runBlocking .

Answer 1

runBlocking ( doc ) 的签名是

fun <T> runBlocking(
    context: CoroutineContext = EmptyCoroutineContext,
    block: suspend CoroutineScope.() -> T
): T (source)

如果您看到 context 参数，它默认为 EmptyCoroutineContext。因此，当您不传递特定上下文时，默认值是当前线程上的事件循环。由于运行 runBlocking block 之前的当前线程是主线程，因此无论您在该 block 内运行什么，都仍在主线程上。

如果你像下面这样传递协程上下文，你就会让 runBlocking 中的 block 在不同的线程中运行。

println("before runBlocking ${Thread.currentThread().name}")

runBlocking(Dispatchers.Default) {
    delay(2000L)
    println("inside runBlocking ${Thread.currentThread().name}")
    delay(2000L)
}

println("after runBlocking ${Thread.currentThread().name}")

输出

before runBlocking main
inside runBlocking DefaultDispatcher-worker-1
after runBlocking main

或者，如果您在不传递上下文的情况下启动 runBlocking，但如下所示在内部启动协程，您会看到它在不同的线程上运行。

println("before runBlocking ${Thread.currentThread().name}")

runBlocking { 
    println("inside runBlocking ${Thread.currentThread().name}")
    delay(2000L) 
    CoroutineScope(Dispatchers.Default).launch {
        println("inside runBlocking coroutineScope ${Thread.currentThread().name}")
    }
    delay(2000L)
}

println("after runBlocking ${Thread.currentThread().name}")

输出

before runBlocking main
inside runBlocking main
inside runBlocking coroutineScope DefaultDispatcher-worker-1
after runBlocking main