Why am I getting this error with OTL?

Question

I am using OTL for the first time and I was trying to use the Async/Await abstraction.

Now, I created a small program just to see what will happen. It's just a button and it calls this procedure.

procedure TForm2.Button1Click(Sender: TObject);
var i : integer;
begin
Button1.enabled := false; //Only for second try

for i := 0 to 100 do
begin

Async(
  procedure begin
    sleep(5000);
end).
Await(
  procedure begin

  //First Try - Button1.Enabled := true;

  //Second Try - showmessage('finished')

  end
);

Button1.enabled := true; //Only for the second try.

  end;
end; 

First Try

For this it works fine the first time, disable the button, sleep for the asyncs and then enable it back.

But the second time I click the button, it is disabled but never gets enabled again.

Second Try

This time I wanted to show a message x100 times and it works the first time aswell, but when I call the procedure again I get the following error TOminCommunicationEndpoint.Send: Queue is full

Can someone who has used this library explain to me, why am I getting this error? And if it is related to the problem with the first try?

Answer 1

It seems you are hitting an internal limitation of OTL.

Each call to Async-Await starts a new thread and returns immediately. When the loop is done you end up with 100 threads, each waiting 5 seconds before executing the Await code.

AFAIK, there is a limitation of 60 concurrent threads in OTL when using the threadpool.