/* Definitions used by the GDB event loop.
   Copyright 1999 Free Software Foundation, Inc.
   Written by Elena Zannoni <ezannoni@cygnus.com> of Cygnus Solutions.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program 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 this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

/* An event loop listens for events from multiple event sources. When
   an event arrives, it is queued and processed by calling the
   appropriate event handler. The event loop then continues to listen
   for more events. An event loop completes when there are no event
   sources to listen on.  External event sources can be plugged into
   the loop.

   There are 3 main components: 
   - a list of file descriptors to be monitored, GDB_NOTIFIER.  
   - a list of events that have occurred, EVENT_QUEUE.  
   - a list of signal handling functions, SIGHANDLER_LIST.

   GDB_NOTIFIER keeps track of the event sources. Event sources for
   gdb are currently the UI and the target.  Gdb communicates with the
   command line user interface via the readline library and usually
   communicates with remote targets via a serial port. Serial ports
   are represented in GDB as file descriptors and select/poll calls.
   For native targets instead, the communication consists of calls to
   ptrace and waits (via signals) or calls to poll/select (via file
   descriptors). In the current gdb, the code handling events related
   to the target resides in the wait_for_inferior function and in
   various target specific files (*-tdep.c).

   EVENT_QUEUE keeps track of the events that have happened during the
   last iteration of the event loop, and need to be processed.  An
   event is represented by a procedure to be invoked in order to
   process the event.  The queue is scanned head to tail.  If the
   event of interest is a change of state in a file descriptor, then a
   call to poll or select will be made to detect it.

   If the events generate signals, they are also queued by special
   functions that are invoked through traditional signal handlers.
   The actions to be taken is response to such events will be executed
   when the SIGHANDLER_LIST is scanned, the next time through the
   infinite loop.  

   Corollary tasks are the creation and deletion of event sources. */

typedef void *gdb_client_data;
struct async_signal_handler;
typedef void (handler_func) (int, gdb_client_data);
typedef void (sig_handler_func) (gdb_client_data);
typedef void (timer_handler_func) (gdb_client_data);

/* Where to add an event onto the event queue, by queue_event. */
typedef enum
  {
    /* Add at tail of queue. It will be processed in first in first
       out order. */
    TAIL,
    /* Add at head of queue. It will be processed in last in first out
       order. */
    HEAD
  }
queue_position;

/* Tell create_file_handler what events we are interested in. 
   This is used by the select version of the event loop. */

#define GDB_READABLE	(1<<1)
#define GDB_WRITABLE	(1<<2)
#define GDB_EXCEPTION	(1<<3)

/* Exported functions from event-loop.c */

extern void start_event_loop (void);
extern void delete_file_handler (int fd);
extern void add_file_handler (int fd, handler_func * proc, gdb_client_data client_data);
extern void mark_async_signal_handler (struct async_signal_handler *async_handler_ptr);
extern struct async_signal_handler *
  create_async_signal_handler (sig_handler_func * proc, gdb_client_data client_data);
extern void delete_async_signal_handler (struct async_signal_handler **async_handler_ptr);
extern int create_timer (int milliseconds, timer_handler_func * proc, gdb_client_data client_data);
extern void delete_timer (int id);
