Re: [RFC] New threadnum command for breakpoints

["Frédéric Riss" <frederic.riss@gmail.com>]

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Le lundi 31 juillet 2006 à 16:00 +0200, Frederic RISS a écrit :
>  I'll follow up soon with a patch doing this.

Here's a code patch for discussion and a tentative doco patch. I've
chosen to initialize the variable early in handle_inferior_event, so
that it's set whatever happens. I thought that if we document it, it'd
rather be always set and not only for breakpoint condition evaluation. 

I'm still wondering about 2 things:

1. Should it change on a user requested thread switch? That would be a
simple patch to thread.c:switch_to_thread. But maybe documenting it as
'the id of the last stopped thread' wouldn't be a bad idea. I don't
think GDB provides a way for the user to get this information (I mean
once he has selected another thread). This way 'thread $_gdb_thread'
would always bring you back to the stopped thread.

2. Should we add support for read-only convenience variables? Writing in
$_gdb_thread makes no sense... but it causes no harm either. We already
have $bpnum in the same situation. I see some ways to support this:
        - Add lval_internalvar_readonly 
        - Add a read_only flag to struct internalvar and check it at
        assignment time. Internal vars are already special-cased there,
        so this should be easy. Would be my solution of choice.
        - Don't create a real convenience variable, but add OP_THREADID
        to expression.h and generate it in write_dollar_var. Also add
        some API to infrun.c to export the stopped threadid.

Fred.

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2006-07-31  Frederic Riss  <frederic.riss@st.com>

	* infrun.c (handle_inferior_event): Set the $_gdb_thread convenience
	variable.  Don't call breakpoint_thread_match anymore.  Suggested by
	Vladimir Prus  <vladimir@codesourcery.com>
	

Index: infrun.c
===================================================================
RCS file: /cvs/src/src/gdb/infrun.c,v
retrieving revision 1.213
diff -u -p -r1.213 infrun.c
--- infrun.c	22 Jul 2006 14:48:03 -0000	1.213
+++ infrun.c	31 Jul 2006 19:26:33 -0000
@@ -1250,6 +1250,10 @@ handle_inferior_event (struct execution_
 
   int sw_single_step_trap_p = 0;
   int stopped_by_watchpoint = -1;	/* Mark as unknown.  */
+  static struct internalvar *gdb_thread_var = NULL;
+
+  if (gdb_thread_var == NULL)
+    gdb_thread_var = lookup_internalvar("_gdb_thread");
 
   /* Cache the last pid/waitstatus. */
   target_last_wait_ptid = ecs->ptid;
@@ -1307,6 +1311,10 @@ handle_inferior_event (struct execution_
       ui_out_text (uiout, "]\n");
     }
 
+  set_internalvar (gdb_thread_var,
+		   value_from_longest (builtin_type_int,
+				       pid_to_thread_id (ecs->ptid)));
+
   switch (ecs->ws.kind)
     {
     case TARGET_WAITKIND_LOADED:
@@ -1589,8 +1597,6 @@ handle_inferior_event (struct execution_
       if (breakpoints_inserted && breakpoint_here_p (stop_pc))
 	{
 	  ecs->random_signal = 0;
-	  if (!breakpoint_thread_match (stop_pc, ecs->ptid))
-	    thread_hop_needed = 1;
 	}
       else if (SOFTWARE_SINGLE_STEP_P () && singlestep_breakpoints_inserted_p)
 	{

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2006-07-31  Frederic Riss  <frederic.riss@st.com>

	* gdb.texinfo (Stopping and starting multi-thread programs): Mention
	the $_gdb_thread convenience variable.



Index: gdb.texinfo
===================================================================
RCS file: /cvs/src/src/gdb/doc/gdb.texinfo,v
retrieving revision 1.345
diff -u -p -r1.345 gdb.texinfo
--- gdb.texinfo	21 Jul 2006 14:46:55 -0000	1.345
+++ gdb.texinfo	31 Jul 2006 19:22:50 -0000
@@ -4208,8 +4208,10 @@ breakpoints on all threads, or on a part
 @cindex breakpoints and threads
 @cindex thread breakpoints
 @kindex break @dots{} thread @var{threadno}
+@vindex $_gdb_thread@r{, convenience variable}
 @item break @var{linespec} thread @var{threadno}
 @itemx break @var{linespec} thread @var{threadno} if @dots{}
+@itemx break @var{linespec} if $_gdb_thread == @var{threadno} @r{[} && @dots@r{]}
 @var{linespec} specifies source lines; there are several ways of
 writing them, but the effect is always to specify some source line.
 
@@ -4231,6 +4233,15 @@ breakpoint condition, like this:
 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
 @end smallexample
 
+Alternatively, you can use the @samp{$_gdb_thread} convenience variable in 
+the breakpoint's condition.  The @samp{$_gdb_thread} variable is set by 
+@value{GDBN} to the thread identifier of the stopped thread.  This can be used 
+for example to make a breakpoint trigger in multiple threads, like this:
+
+@smallexample
+(@value{GDBP}) break frik.c:13 if $_gdb_thread == 8 ||  $_gdb_thread == 9
+@end smallexample
+
 @end table
 
 @cindex stopped threads