When the time is triggered the tread?

Hi :slight_smile:

Very simple example here

1 let t = Thread.create (fun _ -> Printf.printf "hello\n") ();;
2 let _ = Unix.sleep 3;;

In line 1, I triggered thread and expect string of hello is printed to my terminal.

In line 2, I have a some trick to prevent terminating my program before starting the thread.

But, my output will be shown after 3 sec. why?

See this example in C/C++ style.

#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

void *t_function(void *data)

int main() {
        pthread_t t;
        pthread_create(&t, NULL, t_function, NULL);

The string of hello is printed right after start the program and wait 3 sec. this is my expectation and works well.

So, How can I handle the mechanism of thread same as C/C++ ? the example of first program(Ocaml) is not my expectation.

Not running your code, but I notice you’re using Printf.printf. stdout is buffered. IIRC, so is stderr (sigh). So you need to “flush stdout” after the printf, in that thread.

Oh thanks!

This code work, that print out before consumes 3 seconds.

let t = Thread.create (fun _ -> Printf.printf "hello\n"; flush stdout) ();;
let _ =  Unix.sleep 3;;

But this code not works but I don’t know difference between above and below

let t = Thread.create (fun _ -> Printf.printf "hello\n") ();;
let _ =  flush stdout; Unix.sleep 3;;

I suppose flush runs before the thread. Try

let t = Thread.create (fun _ -> Printf.printf "hello\n") ();;
let _ = print_endline "world"; Unix.sleep 3;;

You can use %! in your format string for printf to flush the channel:

let t = Thread.create (fun _ -> Printf.printf "hello\n%!") ()
let () = Unix.sleep 3
1 Like

Oh yes! you are right :slight_smile:

Thank you