1

我有两个在 ViewModel 中并行启动的挂起方法：

init {
    viewModelScope.launch(Dispatchers.Default) {
        launch { loadTotalCirculation() }
        launch { loadMarketPrice() }
    }
}

private suspend fun loadTotalCirculation() {
    val totalCirculation = bitcoinChartsRepository.getTotalCirculation(5, TimeUnit.HOURS)
    _viewState.value = _viewState.value.copy(totalCirculation = chartViewEntityMapper(totalCirculation))
}

private suspend fun loadMarketPrice() {
    val marketPrice = bitcoinChartsRepository.getMarketPrice(27, TimeUnit.DAYS)
    _viewState.value = _viewState.value.copy(marketPrice = chartViewEntityMapper(marketPrice))
}

但是，我想防止_viewState.value = _viewState.value.copy...在我的两种方法中同时执行这些部分。实现这一目标的最佳方法是什么？

4

1 回答 1

3

同步并行协程有多种可能性。可能最简单的方法是创建一个单线程上下文，类似于主线程或使用Mutex。请注意，此互斥锁是专门为 couroutines 设计的，它不是来自 Java 标准库的东西。

单线程上下文：

val context = Executors.newSingleThreadExecutor().asCoroutineDispatcher()

private suspend fun loadTotalCirculation() {
    val totalCirculation = bitcoinChartsRepository.getTotalCirculation(5, TimeUnit.HOURS)
    withContext (context) {
        _viewState.value = _viewState.value.copy(totalCirculation = chartViewEntityMapper(totalCirculation))
    }
}

private suspend fun loadMarketPrice() {
    val marketPrice = bitcoinChartsRepository.getMarketPrice(27, TimeUnit.DAYS)
    withContext (context) {
        _viewState.value = _viewState.value.copy(marketPrice = chartViewEntityMapper(marketPrice))
    }
}

或者，您可以通过以下方式重用主线程，而不是创建自己的线程withContext(Dispatchers.Main)：

互斥体：

val mutex = Mutex()

private suspend fun loadTotalCirculation() {
    val totalCirculation = bitcoinChartsRepository.getTotalCirculation(5, TimeUnit.HOURS)
    mutex.withLock {
        _viewState.value = _viewState.value.copy(totalCirculation = chartViewEntityMapper(totalCirculation))
    }
}

private suspend fun loadMarketPrice() {
    val marketPrice = bitcoinChartsRepository.getMarketPrice(27, TimeUnit.DAYS)
    mutex.withLock {
        _viewState.value = _viewState.value.copy(marketPrice = chartViewEntityMapper(marketPrice))
    }
}

使用主线程或互斥锁可能是首选，因为如果我们创建自己的线程，我们需要确保在不再需要它时正确停止/关闭它。

您可以从官方文档中阅读本文的更多内容：https ://kotlinlang.org/docs/shared-mutable-state-and-concurrency.html

于 2021-06-03T20:18:21.040 回答