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+/* 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.  */
+
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/time.h>
+#include <signal.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/wait.h>
+#include "defs.h"
+
+/* 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
+
+extern void delete_file_handler PARAMS ((int));
+extern void 
+  create_file_handler PARAMS ((int, int, file_handler_func, gdb_client_data));
+extern int gdb_do_one_event PARAMS ((void));
+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));
+