android - Kotlin 中 CoroutineScope 和 coroutineScope 的区别

Question

任何人都可以明确功能之间的关系CoroutineScope()和 coroutineScope() ?

当我试图检查源代码时，我发现它们都是CoroutineScope.kt的函数。 .此外，coroutineScope()是 suspend函数，而另一个是 normal功能

以下是我能找到的文档:

/**
 * Creates a [CoroutineScope] that wraps the given coroutine [context].
 *
 * If the given [context] does not contain a [Job] element, then a default `Job()` is created.
 * This way, cancellation or failure or any child coroutine in this scope cancels all the other children,
 * just like inside [coroutineScope] block.
 */
@Suppress("FunctionName")
public fun CoroutineScope(context: CoroutineContext): CoroutineScope =
    ContextScope(if (context[Job] != null) context else context + Job())

和

/**
 * Creates a [CoroutineScope] and calls the specified suspend block with this scope.
 * The provided scope inherits its [coroutineContext][CoroutineScope.coroutineContext] from the outer scope, but overrides
 * the context's [Job].
 *
 * This function is designed for _parallel decomposition_ of work. When any child coroutine in this scope fails,
 * this scope fails and all the rest of the children are cancelled (for a different behavior see [supervisorScope]).
 * This function returns as soon as the given block and all its children coroutines are completed.
 * A usage example of a scope looks like this:
 *
 * ```
 * suspend fun showSomeData() = coroutineScope {
 *
 *   val data = async(Dispatchers.IO) { // <- extension on current scope
 *      ... load some UI data for the Main thread ...
 *   }
 *
 *   withContext(Dispatchers.Main) {
 *     doSomeWork()
 *     val result = data.await()
 *     display(result)
 *   }
 * }
 * ```
 *
 * The scope in this example has the following semantics:
 * 1) `showSomeData` returns as soon as the data is loaded and displayed in the UI.
 * 2) If `doSomeWork` throws an exception, then the `async` task is cancelled and `showSomeData` rethrows that exception.
 * 3) If the outer scope of `showSomeData` is cancelled, both started `async` and `withContext` blocks are cancelled.
 * 4) If the `async` block fails, `withContext` will be cancelled.
 *
 * The method may throw a [CancellationException] if the current job was cancelled externally
 * or may throw a corresponding unhandled [Throwable] if there is any unhandled exception in this scope
 * (for example, from a crashed coroutine that was started with [launch][CoroutineScope.launch] in this scope).
 */
public suspend fun <R> coroutineScope(block: suspend CoroutineScope.() -> R): R =
    suspendCoroutineUninterceptedOrReturn { uCont ->
        val coroutine = ScopeCoroutine(uCont.context, uCont)
        coroutine.startUndispatchedOrReturn(coroutine, block)
    }

我想弄清楚它们之间的区别。如果有人可以回答何时使用哪一个，那将很有帮助。

Answer 1

CoroutineScope 之间的最佳区别(大写 C 版本)与 coroutineScope (较小的 c 版本)，我可以弄清楚并且很容易理解的是将它们与 相关联非结构化 对比 结构化 并发
让我分享一个例子:

class MainActivity : AppCompatActivity() {
    private lateinit var btn: Button
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        btn = findViewById(R.id.start_btn)
        btn.setOnClickListener {
            CoroutineScope(Dispatchers.Main).launch {
                val result = downloadUserData()
                Toast.makeText(applicationContext, "Result : $result", Toast.LENGTH_LONG).show()
            }
        }
    }

    private suspend fun downloadUserData(): Int {
        var result = 0
        // Here, we use CoroutineScope (Capital C version) which will start a new scope and
        // launch coroutine in new scope Dispatchers.IO, Not In Parent Scope which is Dispatchers.Main
        // Thus, this function would directly return without waiting for loop completion and will return 0
        CoroutineScope(Dispatchers.IO).launch {
            for (i in 0 until 100) {
                kotlinx.coroutines.delay(10)
                result++
            }
        }
        return result
    }
}

输出 : Result : 0这是 的示例非结构化并发不能保证子协程在返回之前完成。因此，调用者/父协程会得到子协程返回的错误值。甚至，当子协程已经返回时，子协程可能正在后台运行(处于 Activity 状态)，这可能导致 内存泄漏 在某些情况下。
解决方案:
当我们需要在多个协程之间进行通信时，我们需要确保 结构化并发 (推荐的)
这可以通过在子/被调用协程内重新使用父/调用者协程范围来完成。这可以通过 coroutineScope {} 来实现(较小的 c)子/被调用协程内的版本。

private suspend fun downloadUserData(): Int {
    var result = 0
    // By using coroutineScope (Smaller c version) below, we ensure that this coroutine would execute in the
    // parent/caller coroutine's scope, so it would make sure that the for loop would complete
    // before returning from this suspended function. This will return 20000 properly
    coroutineScope {
        for (i in 0 until 100) {
            kotlinx.coroutines.delay(10)
            result++
        }
    }
    return result
}

输出: Result : 100