Kotlin 协程 yield() 的目的是什么

发布于03月03日

我不确定yield函数的目的是什么.你能看看我举的这个例子吗？

我正在遵循一个here的例子.

以下是代码:

val job = launch {
    val child = launch {
        try {
            delay(Long.MAX_VALUE)
        } finally {
            println("Child is cancelled")
        }
    }
    yield() //why do i need this ???????
    println("取消子项")
    child.cancel()
    child.join()
    yield()
    println("家长没有被取消")
}
job.join()

When I comment out the first yield I get the following results:

取消子项

家长没有被取消

但如果我保持yield 率不变:

取消子项

Child is cancelled

家长没有被取消

What does it mean to use yield here?

Yields a thread (or thread pool) of the current coroutine dispatcher to other coroutines to run. If the coroutine dispatcher does not have its own thread pool (like Dispatchers.Unconfined) then this function does nothing, but checks if the coroutine Job was completed. This suspending function is cancellable. If the Job of the current coroutine is cancelled or completed when this suspending function is invoked or while this function is waiting for dispatching, it resumes with CancellationException.

它至少可以完成一些事情

It temporarily deprioritises the current long running CPU task, giving other tasks a fair opportunity to run.
Checks whether the current job is cancelled, since otherwise in a tight CPU bound loop, the job may not check until the end.
允许子作业(job)的进度，其中存在争用，因为作业(job)比线程多.如果当前工作应根据其他工作的进展进行调整，这一点可能很重要.