Start multiple Processes and wait till they are finished

Question

I'm trying to start multiple Task which will start a process on a remote maschine. After they concluded a mail should be send.

What should my Code do?: I have multiple Bots running on VMs/Remoteclients to simulate some traffic and im doing some research on their behavior after manipulating the machine and it takes hours to finish. This is done by my main machine that use ps tools to run scripts remotely on them. Basically I start one psexe to start my bot and a psexe to "watch" over the output of the bot. Until now I used 4 programs to let the script run on the 4 machines and one program that was looking after those 4 task if they have finish so it may send me a mail that the task have completed and if it had some errors or smth like that. And tbh its annoying to change always the code in 4 solutions^^ so I though I could make it run asynchrony but in class we only talked about the concept how smth like this may work and now I'm struggling with the different concepts of .net how to implement it. Below I provided a mockup of my code.

void mainClass(){
   doWithThreads(); // this works
   doWithTasks(); // this dosnt work
   doWithTaskAndWait(); // this works again
}

void doWithThreads(){
   Thread t1 = new Thread(() => startBot("Bot1"));
   t1.start();   
   Thread t2 = new Thread(() => startBot("Bot2"));
   t2.start();
   t1.join();
   t2.join();
   sendMail();
}

void async doWithTasks(){
   List<Task> tl = new List<Task>();
   tl.add(Task.Factory.Startnew(() => startBot("Bot3"));
   tl.add(Task.Factory.Startnew(() => startBot("Bot4"));
   await Task.WhenAll(tl); // jumps instantly to sendMail and Task in TL are never started
   sendMail();
}

void doWithTaskAndWait(){
   List<Task> tl = new List<Task>();
   tl.add(Task.Factory.Startnew(() => startBot("Bot5"));
   tl.add(Task.Factory.Startnew(() => startBot("Bot6"));
   Task.WhenAll(tl).Wait(); //I think this works bc its again busy waiting
   sendMail();
}

void startBot(string x){
   Process a = ... //pstoolsconfig
   Process check = ... //pstoolsconfig 
   a.start();
   check.start() // this one checks the logfile of process a
   while(!check.StandardError.ReadToEnd().Contains(x + " has finished")){
      check.start(); //should simulate busy waiting
      thread.sleep(1000) //wait a sec
   }//as soon it finds the phrases "BotX has finished" in the logfile it should be done with his job 

}

Unluckily I don't have anyone who I can ask about it and I don't have any idea why the async/await method doesn't work. My Idea is that the startBot method returns void and bc of this it never can "confirm" that it has finished to run. And the I think that the thread.join and the task.whenall.wait are like busy waiting operations that blocks everything else on the scheduler. But maybe I'm just lucky that those methods find very fast a spot on the scheduler and are executed "faster" then the sendmail.

I hope someone can help me to figure out what I'm doing wrong.

//Update 1:Thats the behavior of doWithTask

List<Task> tl = new List<Task>();
tl.add(Task.Factory.Startnew(() => startBot("Bot3"));
Console.WriteLine(tl.elementat(0).status)); // running 
Task.WhenAll (tl).ContineWith(t => sendMail());
Console.WriteLine(tl.elementat(0).status)); // running
//end of code exe closed

Possible duplicate of [Why exactly is void async bad?](https://stackoverflow.com/questions/45447955/why-exactly-is-void-async-bad) — Sinatr, Feb 14 '19 at 15:55
[`Task.WaitAll(tl.ToArray())`](https://learn.microsoft.com/en-us/dotnet/api/system.threading.tasks.task.waitall?view=netframework-4.7.2#System_Threading_Tasks_Task_WaitAll_System_Threading_Tasks_Task___) — Rufus L, Feb 14 '19 at 15:56

score 1 · Accepted Answer · answered Feb 14 '19 at 16:11

1

Lets have a look why it works like it does at the moment:

Thread.Join Doc

Blocks the calling thread until the thread represented by this instance terminates ...

It 'waits' for the threads (t1, t2) to terminate before continuing with sendMail().

Task.WhenAll Doc

Creates a task that will complete when all of the supplied tasks have completed.

This one does not wait. It is creating another Task an continues on as usual.

Task.WhenAll.Wait Doc

Waits for the Task to complete execution.

This one takes the Task create above and waits for its termination. (Task.WaitAll would have achived the same)

What you can do:

If you want to block the current thread until completion:

Task.WaitAll(tl.ToArray());

If you dont want to block the current thread:

Task.WhenAll(tl).ContinueWith(t => sendMail());

ContinueWith Creates a continuation that executes asynchronously when the target Task completes.

answered Feb 14 '19 at 16:11

Hyarus

922
6
14

This is a great answer but it doesn't help me. My problem is that startBot() is never finished befor the end of the code is reached. As example: List tl = new List(); tl.add(Task.Factory.Startnew(() => startBot("Bot3")); Console.WriteLine(tl.elementat(0).status)); // running Task.WhenAll(tl).ContineWith(t => sendMail()); Console.WriteLine(tl.elementat(0).status)); // running – Kleisophabo Feb 14 '19 at 16:27
@Kleisophabo if you want to wait for startBot() to finish you need to use `Task.WaitAll(tl.ToArray()); sendMail(); Console.WriteLine(tl.elementat(0).status));` or keep extending with ContinueWith `Task.WhenAll(tl).ContinueWith(t => sendMail()).ContinueWith(t => Console.WriteLine(t.status)));` – Hyarus Feb 15 '19 at 09:43
If this does not help you might to want to add your startBot() function. Maybe it is async itself? – Hyarus Feb 15 '19 at 09:44
Well thank you for your help but the only different between the startBot here and mine is a lot of strings to define the parameter to start pstools. – Kleisophabo Feb 15 '19 at 14:49

score 0 · Answer 2 · answered Feb 18 '19 at 10:19

0

Thank you all for your help. I figured it out during the weekend.

I changed the design from my startBot to let it return a Task and then the await did work.

answered Feb 18 '19 at 10:19

Kleisophabo

29
1
6

Start multiple Processes and wait till they are finished

2 Answers2