CoroutineScope的一个用法

在执行下面的composable 函数里代码的时候发现挂起函数 playerOne.run(), playerOne.run()几乎没怎么执行

复制代码

    var raceInProgress by remember { mutableStateOf(true) }

    if (raceInProgress) {
        LaunchedEffect(playerOne, playerTwo) {

            launch() { playerOne.run() }
            launch { playerTwo.run() }

            raceInProgress = false
        }
    }

    suspend fun run() {
        try {
            Log.d("test", "run starts")
            while (currentProgress < maxProgress) {
                Log.d("test", "run: $currentProgress")
                delay(progressDelayMillis)
                currentProgress += progressIncrement
            }
        }catch (e: CancellationException) {
            Log.e("RaceParticipant", "$name: ${e.message}")
            throw e // Always re-throw CancellationException.
        }
    }

日志如下：

复制代码

2026-01-05 23:22:14.761  5941-5941  test                    com.example.racetracker              D  run starts
2026-01-05 23:22:14.761  5941-5941  test                    com.example.racetracker              D  run: 0
2026-01-05 23:22:14.761  5941-5941  test                    com.example.racetracker              D  run starts
2026-01-05 23:22:14.761  5941-5941  test                    com.example.racetracker              D  run: 0
2026-01-05 23:22:14.793  5941-5941  RaceParticipant         com.example.racetracker              E  Player 1: The coroutine scope left the composition
2026-01-05 23:22:14.793  5941-5941  RaceParticipant         com.example.racetracker              E  Player 2: The coroutine scope left the composition

可以看到，coroutine 被取消了。

原因是，launch 函数是非阻塞的，所以两个 launch函数把协程函数 run() 起来后不等 run()执行完即返回，然后把raceInProgress设置为false,触发重组，导致 launchedEffect被移出，从而协程函数run()被取消。

解决方法是把 run函数加入到 coroutineScope里.这个 coroutineScope是阻塞函数，等到run()函数执行完才返回。

复制代码

    var raceInProgress by remember { mutableStateOf(false) }

    if (raceInProgress) {
        LaunchedEffect(playerOne, playerTwo) {
            coroutineScope {
                launch() { playerOne.run() }
                launch { playerTwo.run() }
            }
            raceInProgress = false
        }
    }

coroutineScope的声明如下：

复制代码

package kotlinx.coroutines

public suspend fun <R> coroutineScope(block: suspend CoroutineScope.() -> R): R {
    contract {
        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }
    return suspendCoroutineUninterceptedOrReturn { uCont ->
        val coroutine = ScopeCoroutine(uCont.context, uCont)
        coroutine.startUndispatchedOrReturn(coroutine, block)
    }
}

参考：

https://developer.android.google.cn/codelabs/basic-android-kotlin-compose-coroutines-android-studio?hl=en#5