Kotlin协程介绍（五）挂起函数

矫情吗；* 2023-07-02 07:28 16阅读 0赞

[Kotlin协程介绍（二）实现原理][Kotlin] 中介绍过，挂起函数经过编译后以CPS的形式运行。反之，也可以将CPS转成挂起函数，使之可在协程中使用。这具体是通过suspendCoroutine\{\}或suspendCancellableCoroutine\{\}实现的

public suspend inline fun <T> suspendCoroutine(crossinline block: (Continuation<T>) -> Unit): T =
        suspendCoroutineUninterceptedOrReturn { c: Continuation<T> ->
            val safe = SafeContinuation(c.intercepted())
            block(safe)
            safe.getOrThrow()
        }
    
    public suspend inline fun <T> suspendCancellableCoroutine(
        crossinline block: (CancellableContinuation<T>) -> Unit): T =
        suspendCoroutineUninterceptedOrReturn { uCont ->
            val cancellable = CancellableContinuationImpl(uCont.intercepted(), resumeMode = MODE_CANCELLABLE)
            // 和 suspendCoroutine 的区别就在这里，如果协程已经被取消或者已完成，就会抛出 CancellationException 异常
            cancellable.initCancellability()
            block(cancellable)
            cancellable.getResult()
        }

suspendCoroutine和suspendCancellableCoroutine内部都会调用suspendCoroutineUninterceptedOrReturn，它会返回CPS的Continuation，通过Continuation回调结果或异常。

例如，我们可以将Guava的FutureCallback改造为挂起函数：

suspend fun <T> Future<T>.await(): T = suspendCoroutine {
        Futures.addCallback(this, object: FutureCallback<T> {
            override fun onSuccess(result: T?) {
                if (result != null) {
                    it.resumeWith(Result.success(result))
                }
            }
    
            override fun onFailure(t: Throwable) {
                it.resumeWithException(t)
            }
        })
    }

resumeWith传递执行结果，resumeWithExeption传递异常。

[Kotlin]: https://blog.csdn.net/vitaviva/article/details/104092566