/* Copyright (c) 2007-2018 Dovecot authors, see the included COPYING file */

#include "lib.h"
#include "lib-signals.h"
#include "hash.h"
#include "child-wait.h"

#include <sys/wait.h>

struct child_wait {
	unsigned int pid_count;

	child_wait_callback_t *callback;
	void *context;
};

static int child_wait_refcount = 0;

/* pid_t => wait */
static HASH_TABLE(void *, struct child_wait *) child_pids;

static void
sigchld_handler(const siginfo_t *si ATTR_UNUSED, void *context ATTR_UNUSED);

#undef child_wait_new_with_pid
struct child_wait *
child_wait_new_with_pid(pid_t pid, child_wait_callback_t *callback,
			void *context)
{
	struct child_wait *wait;

	wait = i_new(struct child_wait, 1);
	wait->callback = callback;
	wait->context = context;

	if (pid != (pid_t)-1)
		child_wait_add_pid(wait, pid);
	return wait;
}

void child_wait_free(struct child_wait **_wait)
{
	struct child_wait *wait = *_wait;
	struct hash_iterate_context *iter;
	void *key;
	struct child_wait *value;

	*_wait = NULL;

	if (wait->pid_count > 0) {
		/* this should be rare, so iterating hash is fast enough */
		iter = hash_table_iterate_init(child_pids);
		while (hash_table_iterate(iter, child_pids, &key, &value)) {
			if (value == wait) {
				hash_table_remove(child_pids, key);
				if (--wait->pid_count == 0)
					break;
			}
		}
		hash_table_iterate_deinit(&iter);
	}

	i_free(wait);
}

void child_wait_add_pid(struct child_wait *wait, pid_t pid)
{
	wait->pid_count++;
	hash_table_insert(child_pids, POINTER_CAST(pid), wait);

	lib_signals_set_expected(SIGCHLD, TRUE, sigchld_handler, NULL);
}

void child_wait_remove_pid(struct child_wait *wait, pid_t pid)
{
	wait->pid_count--;
	hash_table_remove(child_pids, POINTER_CAST(pid));

	if (hash_table_count(child_pids) == 0)
		lib_signals_set_expected(SIGCHLD, FALSE, sigchld_handler, NULL);
}

static void
sigchld_handler(const siginfo_t *si ATTR_UNUSED, void *context ATTR_UNUSED)
{
	struct child_wait_status status;

	while ((status.pid = waitpid(-1, &status.status, WNOHANG)) > 0) {
		status.wait = hash_table_lookup(child_pids,
						POINTER_CAST(status.pid));
		if (status.wait != NULL) {
			child_wait_remove_pid(status.wait, status.pid);
			status.wait->callback(&status, status.wait->context);
		}
	}

	if (status.pid == -1 && errno != EINTR && errno != ECHILD)
		i_error("waitpid() failed: %m");
}

void child_wait_switch_ioloop(void)
{
	lib_signals_switch_ioloop(SIGCHLD, sigchld_handler, NULL);
}

void child_wait_init(void)
{
	if (child_wait_refcount++ > 0) {
		child_wait_switch_ioloop();
		return;
	}

	hash_table_create_direct(&child_pids, default_pool, 0);

	lib_signals_set_handler(SIGCHLD, LIBSIG_FLAGS_SAFE,
		sigchld_handler, NULL);
}

void child_wait_deinit(void)
{
	struct hash_iterate_context *iter;
	void *key;
	struct child_wait *value;

	i_assert(child_wait_refcount > 0);
	if (--child_wait_refcount > 0) {
		child_wait_switch_ioloop();
		return;
	}

	lib_signals_unset_handler(SIGCHLD, sigchld_handler, NULL);

	iter = hash_table_iterate_init(child_pids);
	while (hash_table_iterate(iter, child_pids, &key, &value))
		i_free(value);
	hash_table_iterate_deinit(&iter);

	hash_table_destroy(&child_pids);
}