切换异步任务以同步任务

Question

I have the following code:

Task.Factory.ContinueWhenAll(items.Select(p =>
{
    return CreateItem(p);
}).ToArray(), completedTasks => { Console.WriteLine("completed"); });

Is it possible to convert ContinueWhenAll to a synchronous method? I want to switch back between async and sync.

Edit: I should metnion that each of the "tasks" in the continuewhenall method should be executing synchronously.

Answer 1

Unless am mistaken this is what you're looking for

Task.WaitAll(tasks);
//continuation code here

Answer 2

If you want to leave your existing code intact and have a variable option of executing synchronously you should make these changes:

bool isAsync = false; // some flag to check for async operation

var batch = Task.Factory.ContinueWhenAll(items.Select(p =>
{
    return CreateItem(p);
}).ToArray(), completedTasks => { Console.WriteLine("completed"); });

if (!isAsync)
    batch.Wait();

This way you can toggle it programmatically instead of by editing your source code. And you can keep the continuation code the same for both methods.

Edit:

Here is a simple pattern for having the same method represented as a synchronous and async version:

public Item CreateItem(string name)
{
    return new Item(name);
}

public Task<Item> CreateItemAsync(string name)
{
    return Task.Factory.StartNew(() => CreateItem(name));
}

Answer 3

i think you can try this.

using TaskContinuationOptions for a simple scenario.

var taskFactory = new TaskFactory(TaskScheduler.Defau

var random = new Random();
var tasks = Enumerable.Range(1, 30).Select(p => {
    return taskFactory.StartNew(() => {
        var timeout = random.Next(5, p * 50);
        Thread.Sleep(timeout / 2);
        Console.WriteLine(@"  1: ID = " + p);
        return p;
    }).ContinueWith(t => {
        Console.WriteLine(@"* 2: ID = " + t.Result);
    }, TaskContinuationOptions.ExecuteSynchronously);
}).ToArray();

Task.WaitAll(tasks);

or using TPL Dataflow for a complex scenario.

var step2 = new ActionBlock<int>(i => {
    Thread.Sleep(i);
    Console.WriteLine(@"* 2: ID = " + i);
}, new ExecutionDataflowBlockOptions {
    MaxDegreeOfParallelism = 1,
    //MaxMessagesPerTask = 1
});

var random = new Random();
var tasks = Enumerable.Range(1, 50).Select(p => {
    return Task.Factory.StartNew(() => {
        var timeout = random.Next(5, p * 50);
        Thread.Sleep(timeout / 2);
        Console.WriteLine(@"  1: ID = " + p);
        return p;
    }).ContinueWith(t => {
        Thread.Sleep(t.Result);
        step2.Post(t.Result);
    });
}).ToArray();

await Task.WhenAll(tasks).ContinueWith(t => step2.Complete());
await step2.Completion;