gdb/event-loop.h

/* 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 PTR gdb_client_data;
typedef struct gdb_event gdb_event;

typedef void (file_handler_func) PARAMS ((gdb_client_data, int mask));
typedef void (async_handler_func) PARAMS ((gdb_client_data));
typedef void (event_handler_func) PARAMS ((int));

/* Event for the GDB event system.  Events are queued by calling
   async_queue_event and serviced later on by gdb_do_one_event. An
   event can be, for instance, a file descriptor becoming ready to be
   read. Servicing an event simply means that the procedure PROC will
   be called.  We have 2 queues, one for file handlers that we listen
   to in the event loop, and one for the file handlers+events that are
   ready. The procedure PROC associated with each event is always the
   same (handle_file_event).  Its duty is to invoke the handler
   associated with the file descriptor whose state change generated
   the event, plus doing other cleanups adn such. */

struct gdb_event
  {
    event_handler_func *proc;	/* Procedure to call to service this event. */
    int fd;			/* File descriptor that is ready. */
    struct gdb_event *next_event;	/* Next in list of events or NULL. */
  };

/* Information about each file descriptor we register with the event
   loop. */

typedef struct file_handler
  {
    int fd;			/* File descriptor. */
    int mask;			/* Events we want to monitor: POLLIN, etc. */
    int ready_mask;		/* Events that have been seen since
				   the last time. */
    file_handler_func *proc;	/* Procedure to call when fd is ready. */
    gdb_client_data client_data;	/* Argument to pass to proc. */
    struct file_handler *next_file;	/* Next registered file descriptor. */
  }
file_handler;

/* PROC is a function to be invoked when the READY flag is set. This
   happens when there has been a signal and the corresponding signal
   handler has 'triggered' this async_signal_handler for
   execution. The actual work to be done in response to a signal will
   be carried out by PROC at a later time, within process_event. This
   provides a deferred execution of signal handlers.
   Async_init_signals takes care of setting up such an
   asyn_signal_handler for each interesting signal. */

typedef struct async_signal_handler
  {
    int ready;	/* If ready, call this handler from the main event loop, 
				   using invoke_async_handler. */
    struct async_signal_handler *next_handler;	/* Ptr to next handler */
    async_handler_func *proc;	/* Function to call to do the work */
    gdb_client_data client_data;	/* Argument to async_handler_func */
  }
async_signal_handler;

/* 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)

/* Type of the mask arguments to select. */

#ifndef NO_FD_SET
#define SELECT_MASK fd_set
#else
#ifndef _AIX
typedef long fd_mask;
#endif
#if defined(_IBMR2)
#define SELECT_MASK void
#else
#define SELECT_MASK int
#endif
#endif

/* Define "NBBY" (number of bits per byte) if it's not already defined. */

#ifndef NBBY
#define NBBY 8
#endif


/* Define the number of fd_masks in an fd_set */

#ifndef FD_SETSIZE
#ifdef OPEN_MAX
#define FD_SETSIZE OPEN_MAX
#else
#define FD_SETSIZE 256
#endif
#endif
#if !defined(howmany)
#define howmany(x, y) (((x)+((y)-1))/(y))
#endif
#ifndef NFDBITS
#define NFDBITS NBBY*sizeof(fd_mask)
#endif
#define MASK_SIZE howmany(FD_SETSIZE, NFDBITS)


/* Stack for prompts. Each prompt is composed as a prefix, a prompt
   and a suffix. The prompt to be displayed at any given time is the
   one on top of the stack.  A stack is necessary because of cases in
   which the execution of a gdb command requires further input from
   the user, like for instance 'commands' for breakpoints and
   'actions' for tracepoints. In these cases, the prompt is '>' and
   gdb should process input using the asynchronous readline interface
   and the event loop.  In order to achieve this, we need to save
   somewhere the state of GDB, i.e. that it is processing user input
   as part of a command and not as part of the top level command loop.
   The prompt stack represents part of the saved state. Another part
   would be the function that readline would invoke after a whole line
   of input has ben entered. This second piece would be something
   like, for instance, where to return within the code for the actions
   commands after a line has been read.  This latter portion has not
   beeen implemented yet.  The need for a 3-part prompt arises from
   the annotation level. When this is set to 2, the prompt is actually
   composed of a prefix, the prompt itself and a suffix. */

/* At any particular time there will be always at least one prompt on
   the stack, the one being currently displayed by gdb. If gdb is
   using annotation level equal 2, there will be 2 prompts on the
   stack: the usual one, w/o prefix and suffix (at top - 1), and the
   'composite' one with prefix and suffix added (at top). At this
   time, this is the only use of the prompt stack. Resetting annotate
   to 0 or 1, pops the top of the stack, resetting its size to one
   element. The MAXPROMPTS limit is safe, for now. Once other cases
   are dealt with (like the different prompts used for 'commands' or
   'actions') this array implementation of the prompt stack may have
   to change. */

#define MAXPROMPTS 10
struct prompts
  {
    struct
      {
	char *prefix;
	char *prompt;
	char *suffix;
      }
    prompt_stack[MAXPROMPTS];
    int top;
  };

#define PROMPT(X) the_prompts.prompt_stack[the_prompts.top + X].prompt
#define PREFIX(X) the_prompts.prompt_stack[the_prompts.top + X].prefix
#define SUFFIX(X) the_prompts.prompt_stack[the_prompts.top + X].suffix

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

extern void start_event_loop PARAMS ((void));
extern void delete_file_handler PARAMS ((int));
extern void add_file_handler PARAMS ((int, file_handler_func, gdb_client_data));
extern void mark_async_signal_handler PARAMS ((async_signal_handler *));
extern async_signal_handler *
  create_async_signal_handler PARAMS ((async_handler_func *, gdb_client_data));
extern void delete_async_signal_handler PARAMS ((async_signal_handler *async_handler_ptr));

/* Exported functions from event-top.c. 
   FIXME: these should really go into top.h. */

extern void display_gdb_prompt PARAMS ((char*));
extern void async_init_signals PARAMS ((void));
extern void set_async_editing_command PARAMS ((char *, int, struct cmd_list_element *));
extern void set_async_annotation_level PARAMS ((char *, int, struct cmd_list_element *));
extern void set_async_prompt PARAMS ((char *, int, struct cmd_list_element *));
extern void handle_stop_sig PARAMS ((int));
extern void gdb_readline2 PARAMS ((void));

/* Exported variables from event-top.c.
   FIXME: these should really go into top.h. */

extern int async_command_editing_p;
extern char *async_annotation_suffix;
extern char *new_async_prompt;
extern struct prompts the_prompts;
extern void (*call_readline) PARAMS ((void));
extern void (*input_handler) PARAMS ((char *));