Progress printing with threads?

[Simen Kjærås]

On Wednesday, 1 July 2020 at 07:52:28 UTC, AB wrote:
> Hello. I am unsure how to proceed about printing progress in my 
> program.
>
> Suppose the program is processing a very big file and is 
> iterating the file's bytes using a for loop. The processing 
> takes several minutes and I want a progress percentage be 
> printed every 2 seconds in this manner:
>
> Progress: 0.40%
> Progress: 3.20%
> Progress: 5.73%
>
> Is it a good idea to std.concurrency.spawn a new thread and 
> pass to it
>     cast(float)i * 100 / fileSize
> somehow? If not, what's a better way to do this?
>
> This example code shows my situation:
>
>     MmFile  input       = new MmFile(/* ... */);
>     ulong   fileSize    = input.length;
>
>     for (ulong i = 0; i < fileSize; ++i)
>     {
>         // ...
>     }
>
> Thanks in advance.

If doing the update in the same thread that does the processing 
is somehow not an option, this works for me:

import std.concurrency;
import std.stdio;
import core.thread;
import core.time;

void main() {
     ulong filesize = 1234;
     ulong i = 0;
     Tid progress = spawn((shared const(ulong)* p, ulong f){
             while (!receiveTimeout(2000.msecs, (int i){ })) {
                 writeln(*p, "/", f, ": ", *p*100.0/f, "%");
             }
         }, cast(shared)&i, filesize);
     for (; i < filesize; ++i) {
         // Process
     }
     progress.send(0); // Stop
}

There's a cast to shared there which may be suboptimal, but since 
the progress thread is only reading it, I would say it's ok.

--
   Simen