[coredump] close idle connection

[hongzhidao]

Hi!

A rash happens in close idle connection. The main problem is with nxt_conn_accept function.

1. Is it better insert the accepted connection into idle_connections after generating next connection?
   `diff -r 411ed164f393 src/nxt_conn_accept.c
   --- a/src/nxt_conn_accept.c Fri Oct 27 11:05:37 2017 +0300
   +++ b/src/nxt_conn_accept.c Mon Nov 20 03:06:11 2017 -0500
   @@ -191,8 +191,6 @@
   nxt_debug(task, "client: %*s",
   c->remote->address_length, nxt_sockaddr_address(c->remote));

• nxt_queue_insert_head(&task->thread->engine->idle_connections, &c->link);
• c->read_work_queue = lev->work_queue;
  c->write_work_queue = lev->work_queue;

@@ -214,6 +212,8 @@
nxt_work_queue_add(lev->socket.read_work_queue,
lev->accept, task, lev, next);
}
+

• nxt_queue_insert_head(&task->thread->engine->idle_connections, &c->link);
  }`

Since nxt_conn_accept_next may close the connection just generated.

2. The write_state of connection may not be set yet before closed as the previous description.

3. The engine connections forget to decrease after free connection?
   Maybe it's better to add a handy function nxt_conn_free(task, c);

4. The way of free connection is different in the controller (mp_destroy) and router (mp_release) ?

Anyway, the main problem is with closing the idle connections.

Thanks.

[hongzhidao]

`
diff -r 411ed164f393 src/nxt_queue.h
--- a/src/nxt_queue.h Fri Oct 27 11:05:37 2017 +0300
+++ b/src/nxt_queue.h Mon Nov 20 03:26:29 2017 -0500
@@ -161,6 +161,8 @@
do {
(link)->next->prev = (link)->prev;
(link)->prev->next = (link)->next; \

•    (link)->prev = (link);                                                \
  

•    (link)->next = (link);                                                \
  

  } while (0)

#endif
`

It's better to combine nxt_queue_remove and nxt_queue_self.