[RFC v5 6/8] fix py-finish-breakpoint.exp with always-async

[Tom Tromey <tromey@redhat.com>]

With target async enabled, py-finish-breakpoint.exp will trigger an
assertion failure.

The failure occurs because execute_command re-enters the event loop in
some circumstances, and in this case resets the sync_execution flag.
Then later gdb reaches this assertion in normal_stop:

      gdb_assert (sync_execution || !target_can_async_p ());

execute_command has a comment explaining why it dispatches events:

      /* If the interpreter is in sync mode (we're running a user
	 command's list, running command hooks or similars), and we
	 just ran a synchronous command that started the target, wait
	 for that command to end.  */

However, the code did not follow this comment -- it didn't check to
see if the command started the target, just whether the target was
executing a sync command at this point.

This patch fixes the problem by noting whether the target was
executing in sync_execution mode before running the command, and then
augmenting the condition to test this as well.

2013-10-30  Tom Tromey  <tromey@redhat.com>

	PR gdb/14135:
	* top.c (execute_command): Only dispatch events if command
	started target.
---
 gdb/ChangeLog | 6 ++++++
 gdb/top.c     | 4 +++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/gdb/top.c b/gdb/top.c
index e1a1331..fa20025 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -406,6 +406,8 @@ execute_command (char *p, int from_tty)
     {
       const char *cmd = p;
       char *arg;
+      int was_sync = sync_execution;
+
       line = p;
 
       /* If trace-commands is set then this will print this command.  */
@@ -461,7 +463,7 @@ execute_command (char *p, int from_tty)
 	 command's list, running command hooks or similars), and we
 	 just ran a synchronous command that started the target, wait
 	 for that command to end.  */
-      if (!interpreter_async && sync_execution)
+      if (!interpreter_async && !was_sync && sync_execution)
 	{
 	  while (gdb_do_one_event () >= 0)
 	    if (!sync_execution)
-- 
1.8.1.4