使Kotlin暂停函数可取消

import kotlinx.coroutines.*

fun main() {
    val job = GlobalScope.launch {
        val result = withTimeoutOrNull(5000) {
            longRunningOperation()
        }
        
        if (result != null) {
            println("操作成功: $result")
        } else {
            println("操作超时")
        }
    }
    
    // 模拟取消操作
    delay(3000)
    job.cancel()
    
    // 等待协程执行完毕
    runBlocking {
        job.join()
    }
}

suspend fun longRunningOperation(): String {
    delay(6000)
    return "操作完成"
}