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/*
  This file is part of Anastasis
  Copyright (C) 2020 Taler Systems SA

  Anastasis is free software; you can redistribute it and/or modify it under the
  terms of the GNU Lesser General Public License as published by the Free Software
  Foundation; either version 3, or (at your option) any later version.

  Anastasis is distributed in the hope that it will be useful, but WITHOUT ANY
  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

  You should have received a copy of the GNU General Public License along with
  Anastasis; see the file COPYING.GPL.  If not, see <http://www.gnu.org/licenses/>
*/
/**
 * @file util/child_management.c
 * @brief anastasis child management
 * @author Christian Grothoff
 * @author Dominik Meister
 */
#include "platform.h"
#include "anastasis_util_lib.h"


/**
 * Struct which defines a Child Wait handle
 */
struct ANASTASIS_ChildWaitHandle
{
  /**
   * Linked list to the next child
   */
  struct ANASTASIS_ChildWaitHandle *next;
  /**
   * Linked list to the previous child
   */
  struct ANASTASIS_ChildWaitHandle *prev;
  /**
   * Child process which is managed
   */
  struct GNUNET_OS_Process *proc;
  /**
   * Callback which is called upon completion/death of the child task
   */
  ANASTASIS_ChildCompletedCallback cb;
  /**
   * Closure for the handle
   */
  void *cb_cls;
};


/**
 * Pipe used to communicate shutdown via signal.
 */
static struct GNUNET_DISK_PipeHandle *sigpipe;

static struct GNUNET_SIGNAL_Context *shc_chld;

static struct GNUNET_SCHEDULER_Task *sig_task;

static struct ANASTASIS_ChildWaitHandle *cwh_head;

static struct ANASTASIS_ChildWaitHandle *cwh_tail;

/**
 * Task triggered whenever we receive a SIGCHLD (child
 * process died) or when user presses CTRL-C.
 *
 * @param cls closure, NULL
 */
static void
maint_child_death (void *cls)
{
  char buf[16];
  const struct GNUNET_DISK_FileHandle *pr;
  struct ANASTASIS_ChildWaitHandle *nxt;

  (void) cls;
  sig_task = NULL;
  /* drain pipe */
  pr = GNUNET_DISK_pipe_handle (sigpipe,
                                GNUNET_DISK_PIPE_END_READ);
  GNUNET_assert (! GNUNET_DISK_handle_invalid (pr));

  (void) GNUNET_DISK_file_read (pr,
                                buf,
                                sizeof(buf));

  /* find applicable processes that exited */
  for (struct ANASTASIS_ChildWaitHandle *cwh = cwh_head;
       NULL != cwh;
       cwh = nxt)
  {
    enum GNUNET_OS_ProcessStatusType type;
    long unsigned int exit_code = 0;

    nxt = cwh->next;
    if (GNUNET_OK ==
        GNUNET_OS_process_status (cwh->proc,
                                  &type,
                                  &exit_code))
    {
      GNUNET_CONTAINER_DLL_remove (cwh_head,
                                   cwh_tail,
                                   cwh);
      cwh->cb (cwh->cb_cls,
               type,
               exit_code);
      GNUNET_free (cwh);
    }
  }
  if (NULL == cwh_head)
    return;
  /* wait for more */
  sig_task = GNUNET_SCHEDULER_add_read_file (
    GNUNET_TIME_UNIT_FOREVER_REL,
    GNUNET_DISK_pipe_handle (sigpipe,
                             GNUNET_DISK_PIPE_END_READ),
    &maint_child_death,
    NULL);
}


/**
 * Signal handler called for SIGCHLD.  Triggers the
 * respective handler by writing to the trigger pipe.
 */
static void
sighandler_child_death (void)
{
  static char c;
  int old_errno = errno; /* back-up errno */

  GNUNET_break (
    1 ==
    GNUNET_DISK_file_write (GNUNET_DISK_pipe_handle (sigpipe,
                                                     GNUNET_DISK_PIPE_END_WRITE),
                            &c,
                            sizeof(c)));
  errno = old_errno; /* restore errno */
}


void __attribute__ ((constructor))
child_management_start ()
{
  if (NULL != sigpipe)
    return; /* already initialized */
  sigpipe = GNUNET_DISK_pipe (GNUNET_DISK_PF_NONE);
  GNUNET_assert (sigpipe != NULL);
  shc_chld =
    GNUNET_SIGNAL_handler_install (GNUNET_SIGCHLD, &sighandler_child_death);
}


struct ANASTASIS_ChildWaitHandle *
ANASTASIS_wait_child (struct GNUNET_OS_Process *proc,
                      ANASTASIS_ChildCompletedCallback cb,
                      void *cb_cls)
{
  struct ANASTASIS_ChildWaitHandle *cwh;

  child_management_start ();
  cwh = GNUNET_new (struct ANASTASIS_ChildWaitHandle);
  cwh->proc = proc;
  cwh->cb = cb;
  cwh->cb_cls = cb_cls;
  GNUNET_CONTAINER_DLL_insert (cwh_head,
                               cwh_tail,
                               cwh);
  if (NULL == sig_task)
  {
    sig_task = GNUNET_SCHEDULER_add_read_file (
      GNUNET_TIME_UNIT_FOREVER_REL,
      GNUNET_DISK_pipe_handle (sigpipe,
                               GNUNET_DISK_PIPE_END_READ),
      &maint_child_death,
      NULL);
  }
  return cwh;
}


void
ANASTASIS_wait_child_cancel (struct ANASTASIS_ChildWaitHandle *cwh)
{
  GNUNET_CONTAINER_DLL_remove (cwh_head,
                               cwh_tail,
                               cwh);
  if (NULL == cwh_head)
  {
    GNUNET_SCHEDULER_cancel (sig_task);
    sig_task = NULL;
  }
  GNUNET_free (cwh);
}


/**
 * Clean up.
 */
void __attribute__ ((destructor))
ANASTASIS_CM_done ()
{
  GNUNET_assert (NULL == sig_task);
  GNUNET_SIGNAL_handler_uninstall (shc_chld);
  shc_chld = NULL;
  GNUNET_DISK_pipe_close (sigpipe);
  sigpipe = NULL;
}