[RFC] Using bt command in async mode

[Nick Roberts <nickrob@snap.net.nz>]

This patch allows the bt to be executed in async mode while the inferior is
executing.  The idea being that the frontend can get a snapshot of what the
inferior is doing and update the UI.  It's just a proof of concept, so I've
used linux_nat_async_events and my_waitpid directly but eventually these could
be made into target methods, of course.

If the general idea is agreeable, I would like to extend it to other commands
like "info locals", "info threads" etc.

An example session looks like this:

 
    (gdb) maintenance set linux-async on
    (gdb) r&
    Starting program: /home/nickrob/donowt 
    (gdb) bt
    #0  0x080483c9 in mysub1 () at donowt.c:12
    #1  0x080483f7 in mysub () at donowt.c:22
    #2  0x0804840f in main () at donowt.c:28
    (gdb) interrupt
    (gdb) 
    Program received signal SIGINT, Interrupt.
    0x080483c9 in mysub1 () at donowt.c:12
    12            if (i == 5)

    (gdb) quit
    The program is running.  Quit anyway (and kill it)? (y or n) y
    nickrob@kahikatea:~$ 


-- 
Nick                                           http://www.inet.net.nz/~nickrob


2008-04-01  Nick Roberts  <nickrob@snap.net.nz>

	* stack.c (backtrace_command): Make it work in async mode when
	the target is executing.

	* top.c (execute_command): Enable bt command in async mode.

	* inferior.h: New externs

	* linux-nat.c (linux_nat_async_events, my_waitpid):  Make
	non-static.


*** stack.c	18 Mar 2008 08:32:24 +1200	1.164
--- stack.c	01 Apr 2008 12:58:57 +1200	
*************** static void
*** 1285,1293 ****
  backtrace_command (char *arg, int from_tty)
  {
    struct cleanup *old_chain = NULL;
!   int fulltrace_arg = -1, arglen = 0, argc = 0;
    struct backtrace_command_args btargs;
  
    if (arg)
      {
        char **argv;
--- 1285,1306 ----
  backtrace_command (char *arg, int from_tty)
  {
    struct cleanup *old_chain = NULL;
!   int fulltrace_arg = -1, arglen = 0, argc = 0, restart = 0;
    struct backtrace_command_args btargs;
  
+    if (target_executing)
+      {
+        int status, options, async_events_were_enabled;
+ 
+        /* Must be async to get here.  */
+        async_events_were_enabled = linux_nat_async_events (0);
+        target_stop ();
+        my_waitpid (PIDGET (inferior_ptid), &status, 0);
+        if (async_events_were_enabled)
+ 	 linux_nat_async_events (1);
+        restart = 1;
+      }
+ 
    if (arg)
      {
        char **argv;
*************** backtrace_command (char *arg, int from_t
*** 1342,1347 ****
--- 1355,1363 ----
  
    if (old_chain)
      do_cleanups (old_chain);
+ 
+   if (restart)
+     continue_command ("&", 0);
  }
  
  static void


*** top.c	01 Apr 2008 13:47:11 +1200	1.137
--- top.c	01 Apr 2008 13:35:00 +1200	
*************** execute_command (char *p, int from_tty)
*** 463,469 ****
  	    && strcmp (c->name, "pwd") != 0
  	    && strcmp (c->name, "show") != 0
  	    && strcmp (c->name, "info") != 0
! 	    && strcmp (c->name, "interrupt") != 0)
  	  error (_("Cannot execute this command while the target is running."));
  
        /* Pass null arg rather than an empty one.  */
--- 463,470 ----
  	    && strcmp (c->name, "pwd") != 0
  	    && strcmp (c->name, "show") != 0
  	    && strcmp (c->name, "info") != 0
! 	    && strcmp (c->name, "interrupt") != 0
! 	    && strcmp (c->name, "bt") != 0)
  	  error (_("Cannot execute this command while the target is running."));
  
        /* Pass null arg rather than an empty one.  */


*** inferior.h	30 Jan 2008 11:18:32 +1300	1.87
--- inferior.h	01 Apr 2008 09:24:04 +1200	
*************** struct regcache;
*** 49,54 ****
--- 49,57 ----
  
  struct inferior_status;
  
+ extern int my_waitpid (int pid, int *status, int flags);
+ extern int linux_nat_async_events (int enable);
+ 
  extern struct inferior_status *save_inferior_status (int);
  
  extern void restore_inferior_status (struct inferior_status *);

*** linux-nat.c	26 Mar 2008 08:51:33 +1200	1.80
--- linux-nat.c	01 Apr 2008 13:10:00 +1200	
*************** static volatile int linux_nat_num_queued
*** 176,182 ****
     target events are blocked.  */
  static int linux_nat_async_events_enabled;
  
- static int linux_nat_async_events (int enable);
  static void pipe_to_local_event_queue (void);
  static void local_event_queue_to_pipe (void);
  static void linux_nat_event_pipe_push (int pid, int status, int options);
--- 176,181 ----
*************** linux_tracefork_child (void)
*** 350,356 ****
  /* Wrapper function for waitpid which handles EINTR, and checks for
     locally queued events.  */
  
! static int
  my_waitpid (int pid, int *status, int flags)
  {
    int ret;
--- 349,355 ----
  /* Wrapper function for waitpid which handles EINTR, and checks for
     locally queued events.  */
  
! int
  my_waitpid (int pid, int *status, int flags)
  {
    int ret;
*************** async_sigchld_handler (int signo)
*** 3820,3826 ****
  
  /* Enable or disable async SIGCHLD handling.  */
  
! static int
  linux_nat_async_events (int enable)
  {
    int current_state = linux_nat_async_events_enabled;
--- 3819,3825 ----
  
  /* Enable or disable async SIGCHLD handling.  */
  
! int
  linux_nat_async_events (int enable)
  {
    int current_state = linux_nat_async_events_enabled;