ThreadLocal/CoroutineContext 弥合差距

Question

我想在线程级别或协程级别维护一个对象，具体取决于应用程序在不同线程/协程中执行的工作类型。有没有办法实现这个目标？

为了简单起见，我可以编写一个 Spring Boot 应用程序，其中许多事情都是基于线程发生的，并且只有代码的某些部分使用协程来利用它们的好处。如何根据当前执行维护状态？有办法做到这一点吗？

Answer 1

也许我的回答有点晚了，但你可以通过其中之一来做到

1. ContinuationInterceptor

2. CopyableThreadContextElement

提供了更详细的答案和示例这里。

下面我将展示从这些答案复制的

ContinuationInterceptor

的示例。

class WrappedDispatcher(
    private val dispatcher: ContinuationInterceptor,
    private var savedCounter: Int = counterThreadLocal.get() ?: 0
) : AbstractCoroutineContextElement(ContinuationInterceptor), ContinuationInterceptor {
    override fun <T> interceptContinuation(continuation: Continuation<T>): Continuation<T> =
        dispatcher.interceptContinuation(ContinuationWrapper(continuation))

    private inner class ContinuationWrapper<T>(val base: Continuation<T>) : Continuation<T> by base {

        override fun resumeWith(result: Result<T>) {
            counterThreadLocal.set(savedCounter)
            try {
                base.resumeWith(result)
            } finally {
                savedCounter = counterThreadLocal.get()
            }
        }
    }
}

及使用方法

val counterThreadLocal: ThreadLocal<Int> = ThreadLocal()

fun showCounter() {
    println("-------------------------------------------------")
    println("Thread: ${Thread.currentThread().name}\n Counter value: ${counterThreadLocal.get()}")
}

fun main() {
    runBlocking(WrappedDispatcher(Dispatchers.IO)) {
        showCounter()
        counterThreadLocal.set(2)
        delay(100)
        showCounter()
        counterThreadLocal.set(3)
        withContext(WrappedDispatcher(Dispatchers.Default)) {
            println("__________NESTED START___________")
            counterThreadLocal.set(4)
            showCounter()
            println("__________NESTED END_____________")
        }
        delay(100)
        showCounter()
    }
}

输出将是

-------------------------------------------------
Thread: DefaultDispatcher-worker-1
 Counter value: 0
-------------------------------------------------
Thread: DefaultDispatcher-worker-1
 Counter value: 2
__________NESTED START___________
-------------------------------------------------
Thread: DefaultDispatcher-worker-3
 Counter value: 4
__________NESTED END_____________
-------------------------------------------------
Thread: DefaultDispatcher-worker-3
 Counter value: 3