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Re: [libmicrohttpd] Double regarding suspended connection and pthread_ex

From: silvioprog
Subject: Re: [libmicrohttpd] Double regarding suspended connection and pthread_exit
Date: Mon, 16 Mar 2020 17:16:04 -0300

On Mon, Mar 16, 2020 at 4:29 PM Christian Grothoff <address@hidden> wrote:
This seems kind-of OK (I personally think pthread_detach is always messy
and in 99.9% of cases a bad idea).

Hm... Could you point the disadvantages of using detached threads? I'm a little newbie with this feature of pthreads.

I'm going to use suspend/resume and pthread in requests that takes a long time processing read-only data (e.g. report generation) that could block the main loop, but "discard" them if the server stops.

hat you do need to (somehow) ensure
is that you do MHD_resume_connection() (and let it finish) *before*
calling MHD_stop_daemon().

The current design looks like this: 

static void *bar_cb(void *cls) {
  MHD_resume_connection(... con sent with cls above ...);
  ... calls the user-defined callback sent with cls above ...
  return NULL;

// foo() is called inside a MHD_AccessHandlerCallback

int foo(... some params ...) {
  ... some param checking ...
  ret =
    pthread_create(detached_thread, NULL, bar_cb, cls);
  if (ret != 0)
    goto error;
  ret = pthread_detach(detached_thread);
  if (ret != 0)
    goto error;
  return 0;
  ... some error handling ...
  return ret;

The MHD_resume_connection() was called before calling the user-defined callback to avoid "MHD_stop_daemon() called while we have suspended connections". :-)

BTW I'm OK to remove the pthread_detach() if it could raise future problems in my application.

Silvio Clécio

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