我的代码（SendPingAsync）有什么问题

Question

Im writing a C# Ping-Application. I started with a synchronous Ping-method, but I figurred out that pinging several server with one click takes more and more time. So I decided to try the asynchronous method.

Can someone help me out?

public async Task<string> CustomPing(string ip, int amountOfPackets, int sizeOfPackets)
{
    // timeout
    int Timeout = 2000;
    // PaketSize logic
    string packet = "";
    for (int j = 0; j < sizeOfPackets; j++)
    {
        packet += "b";
    };
    byte[] buffer = Encoding.ASCII.GetBytes(packet);
    // time-var
    long ms = 0;
    // Main Method
    using (Ping ping = new Ping())
        for (int i = 0; i < amountOfPackets; i++)
        {
            PingReply reply = await ping.SendPingAsync(ip, Timeout, buffer);
            ms += reply.RoundtripTime;
        };
    return (ms / amountOfPackets + " ms");
};

I defined a "Server"-Class (Ip or host, City, Country).

Then I create a "server"-List:

List<Server> ServerList = new List<Server>()
            {
                new Server("www.google.de", "Some City,", "Some Country")
};

Then I loop through this list and I try to call the method like this:

foreach (var server in ServerList)
ListBox.Items.Add("The average response time of your custom server is: " + server.CustomPing(server.IP, amountOfPackets, sizeOfPackets));

Unfortunately, this is much more competitive than the synchronous method, and at the point where my method should return the value, it returns

System.Threading.Tasks.Taks`1[System.string]

Answer 1

The class System.Threading.Tasks.Task<TResult> is a helper class for Multitasking. While it resides in the Threading Namespace, it works for Threadless Multitasking just as well. Indeed if you see a function return a task, you can usually use it for any form of Multitasking. Tasks are very agnostic in how they are used. You can even run it synchronously, if you do not mind that little extra overhead of having a Task doing not a lot.

Task helps with some of the most important rules/convetions of Multitasking:

• Do not accidentally swallow exceptions. Threadbase Multitasking is notoriously good in doing just that.
• Do not use the result after a cancelation

It does that by throwing you exceptions in your face (usually the Aggregate one) if you try to access the Result Property when convention tells us you should not do that.

As well as having all those other usefull properties for Multitasking.

Answer 2

since you have an async method it will return the task when it is called like this:

Task<string> task = server.CustomPing(server.IP, amountOfPackets, sizeOfPackets);

when you add it directly to your ListBox while concatenating it with a string it will use the ToString method, which by default prints the full class name of the object. This should explaint your output:

System.Threading.Tasks.Taks`1[System.string]

The [System.string] part actually tells you the return type of the task result. This is what you want, and to get it you would need to await it! like this:

foreach (var server in ServerList)
   ListBox.Items.Add("The average response time of your custom server is: " + await server.CustomPing(server.IP, amountOfPackets, sizeOfPackets));

1) this has to be done in another async method and

2) this will mess up all the parallelity that you are aiming for. Because it will wait for each method call to finish.

What you can do is to start all tasks one after the other, collect the returning tasks and wait for all of them to finish. Preferably you would do this in an async method like a clickhandler:

private async void Button1_Click(object sender, EventArgs e)
{
    Task<string> [] allTasks = ServerList.Select(server => server.CustomPing(server.IP, amountOfPackets, sizeOfPackets)).ToArray();
    // WhenAll will wait for all tasks to finish and return the return values of each method call
    string [] results = await Task.WhenAll(allTasks);
    // now you can execute your loop and display the results:
    foreach (var result in results)
    {
        ListBox.Items.Add(result);
    }

}