When the time is triggered the tread?

Learning
1

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)
{
   printf("hello\n");
}

int main() {
        pthread_t t;
        pthread_create(&t, NULL, t_function, NULL);
        sleep(3);
}

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.

2

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.

3

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;;
4

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
5

Oh yes! you are right :slight_smile:

Thank you