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社区首页 >问答首页 >任务与连续调度

问任务与连续调度
EN

Stack Overflow用户
提问于 2016-04-21 06:44:06
回答 1查看 274关注 0票数 1

假设我有许多CPU密集型任务被转储到默认调度程序中(所有这些任务都一次运行，例如通过Task.Run或带有默认调度程序的Task.Factory.StartNew运行)。每个任务都有一个延续。调度程序将启动一些任务，并将其置于运行状态。当这些任务完成后，调度程序就会将原始任务和延续任务混合在队列中来调度，并且必须在两者之间进行选择。它是如何将连续任务与运行更多的组织任务进行排序的。具体来说，如果一个任务已经完成，并且它有一个连续，那么该延续在调度程序中获得优先级，而不是其他已经排队的任务。

例如，假设sheduler运行多个(T1 & T2)排队任务中的2(T1...Tn&T1...Tn)。当其中一个完成时，调度程序会运行延续C1，还是决定启动T3？它会选择哪一种决定论呢？调度程序是否会选择运行更多的任务，并且在T1结束和它的继续C1开始之间可能会有相当大的延迟？

更新:我运行了一些示例代码并添加了一个答案-，但是我仍然想知道这种观察到的行为是否得到了保证？。

task
taskscheduler
c#
multithreading
task-parallel-library
EN

回答 1

Stack Overflow用户

发布于 2016-04-21 07:08:28

所以我试了一个样本：

代码语言：javascript
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var continuations = new List<Task>();
for (int i = 0; i < 20; i++) {
    int counter = i;
    var continuation = Task.Run(() => {
        Console.WriteLine($"T{counter}: Start.");
        Thread.Sleep(500);
        Console.WriteLine($"T{counter}: Complete.");
    }).ContinueWith(t => {
        Console.WriteLine($"C{counter}: Start.");
        Thread.Sleep(50);
        Console.WriteLine($"C{counter}: Complete.");
    });
    continuations.Add(continuation);
}
Task.WaitAll(continuations.ToArray());

哪个输出-，这意味着调度程序确实优先于启动一个新任务(但这是保证的吗？)：

代码语言：javascript
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T1: Start.
T2: Start.
T3: Start.
T0: Start.
T1: Complete.
T2: Complete.
T3: Complete.
C1: Start.
C3: Start.
T0: Complete.
C0: Start.
C2: Start.
C1: Complete.
T4: Start.
C3: Complete.
T5: Start.
C0: Complete.
T6: Start.
C2: Complete.
T7: Start.
T4: Complete.
C4: Start.
T5: Complete.
C5: Start.
T6: Complete.
C6: Start.
T7: Complete.
C7: Start.
C4: Complete.
C5: Complete.
T9: Start.
T8: Start.
C7: Complete.
T10: Start.
C6: Complete.
T11: Start.
T8: Complete.
C8: Start.
T9: Complete.
C9: Start.
T11: Complete.
C11: Start.
T10: Complete.
C10: Start.
C9: Complete.
C8: Complete.
T13: Start.
T12: Start.
C11: Complete.
T14: Start.
C10: Complete.

变体。这里，在启动Task和注册延续之间的调用线程上有额外的执行。

代码语言：javascript
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var continuations = new List<Task>();
for (int i = 0; i < 20; i++) {
    int counter = i;
    var task = Task.Run(() => {
        Console.WriteLine($"T{counter}: Start.");
        Thread.Sleep(500);
        Console.WriteLine($"T{counter}: Complete.");
    });
    Thread.Sleep(100); // Do some stuff before registering continuation.
    var continuation = task.ContinueWith(t => {
    Console.WriteLine($"C{counter}: Start.");
        Thread.Sleep(150);
        Console.WriteLine($"C{counter}: Complete.");
    });
    continuations.Add(continuation);
}
Task.WaitAll(continuations.ToArray());

结果与上述情况相同，即任务N的延拓被赋予其他排队任务的优先级。

代码语言：javascript
运行
复制
T0: Start.
T1: Start.
T2: Start.
T3: Start.
T0: Complete.
C0: Start.
T1: Complete.
C1: Start.
C0: Complete.
T4: Start.
T2: Complete.
C2: Start.
C1: Complete.
T5: Start.
T3: Complete.
C3: Start.
C2: Complete.
T6: Start.
C3: Complete.
T7: Start.
T4: Complete.
C4: Start.
T5: Complete.
C5: Start.
C4: Complete.
T8: Start.
T6: Complete.
C6: Start.
C5: Complete.
T9: Start.
T7: Complete.
C7: Start.
C6: Complete.
T10: Start.
C7: Complete.
T11: Start.
T8: Complete.
C8: Start.
T9: Complete.
C9: Start.
C8: Complete.
T12: Start.
T10: Complete.
C10: Start.
C9: Complete.
T13: Start.
T11: Complete.
C11: Start.
T14: Start.
C10: Complete.
T15: Start.
C11: Complete.
T16: Start.
T12: Complete.
C12: Start.
T13: Complete.
C13: Start.
T14: Complete.
C14: Start.
C12: Complete.
T17: Start.
T15: Complete.
C15: Start.......

另一个变体。在这里，所有任务都先在scheuler上排队(并且可以被调度为运行)，然后再注册连续程序。

代码语言：javascript
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复制
const int taskCount = 20;
var tasks = new List<Task>();
for (int i = 0; i < taskCount; i++) {
    int counter = i;
    var task = Task.Run(() => {
        Console.WriteLine($"T{counter}: Start.");
        Thread.Sleep(500);
        Console.WriteLine($"T{counter}: Complete.");
    });
    tasks.Add(task);
}
Thread.Sleep(400);
var continuations = new List<Task>();
for (int i = 0; i < taskCount; i++) {
    int counter = i;
    var continuation = tasks[i].ContinueWith(t => {
        Console.WriteLine($"C{counter}: Start.");
        Thread.Sleep(150);
        Console.WriteLine($"C{counter}: Complete.");
    });
    continuations.Add(continuation);
}
Task.WaitAll(continuations.ToArray());

结果和以前一样--延续优先。

代码语言：javascript
运行
复制
T0: Start.
T2: Start.
T3: Start.
T1: Start.
T1: Complete.
T3: Complete.
T0: Complete.
T2: Complete.
C2: Start.
C0: Start.
C3: Start.
C1: Start.
C2: Complete.
C1: Complete.
C0: Complete.
C3: Complete.
T7: Start.
T4: Start.
T6: Start.
T5: Start.
T6: Complete.
T5: Complete.
T7: Complete.
T4: Complete.
C6: Start.
C5: Start.
C7: Start.
C4: Start.
C7: Complete.
T8: Start.
C5: Complete.
T9: Start.
C6: Complete.
T10: Start.
C4: Complete.
T11: Start.
T8: Complete.
C8: Start.
T10: Complete.
C10: Start.
T9: Complete.
C9: Start.
T11: Complete.
C11: Start.
C8: Complete.
T12: Start.
C9: Complete.
T13: Start.
C10: Complete.
T14: Start.
C11: Complete.
T15: Start.
T14: Complete.
T12: Complete.
C12: Start.
T13: Complete.
C13: Start.
C14: Start.
T15: Complete.
C15: Start.
T16: Start.
C12: Complete.
C13: Complete.
T18: Start.
T17: Start.
C14: Complete.
T19: Start.
C15: Complete.
T16: Complete.
C16: Start.
T18: Complete.
C18: Start.
T17: Complete.
T19: Complete.
C19: Start.
C16: Complete.
C17: Start.
C18: Complete.
C19: Complete.
C17: Complete.
票数 0
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：

https://stackoverflow.com/questions/36761619

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