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Avoid constant stream of TARGET_WAITKIND_NO_RESUMED

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If we hit the synchronous execution command case described by
handle_no_resumed, and handle_no_resumed determines that the event
should be ignored, because it found a thread that is executing, we end
up in prepare_to_wait.

There, if the current target is not registered in the event loop right
now, we call mark_infrun_async_event_handler.  With that event handler
marked, the event loop calls again into fetch_inferior_event, which
calls target_wait, which returns TARGET_WAITKIND_NO_RESUMED, and we
end up in handle_no_resumed, again ignoring the event and marking
infrun_async_event_handler.  The result is that GDB is now always
keeping the CPU 100% busy in this loop, even though it continues to be
able to react to input and to real target events, because we still go
through the event-loop.

The problem is that marking of the infrun_async_event_handler in
prepare_to_wait.  That is there to handle targets that don't support
asynchronous execution.  So the correct predicate is whether async
execution is supported, not whether the target is async right now.

gdb/ChangeLog:

	PR gdb/26199
	* infrun.c (prepare_to_wait): Check target_can_async_p instead of
	target_is_async_p.
This commit is contained in:
Pedro Alves 2020-07-04 19:31:21 +01:00 committed by Pedro Alves
parent 43667cc6f6
commit 42bd97a6b1
2 changed files with 11 additions and 1 deletions
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6
gdb/ChangeLog
View File

@ -1,3 +1,9 @@
2020-07-10 Pedro Alves <pedro@palves.net>
PR gdb/26199
* infrun.c (prepare_to_wait): Check target_can_async_p instead of
target_is_async_p.
2020-07-10 Pedro Alves <pedro@palves.net>
PR gdb/26199

6
gdb/infrun.c
View File

@ -8116,7 +8116,11 @@ prepare_to_wait (struct execution_control_state *ecs)
ecs->wait_some_more = 1;
if (!target_is_async_p ())
/* If the target can't async, emulate it by marking the infrun event
handler such that as soon as we get back to the event-loop, we
immediately end up in fetch_inferior_event again calling
target_wait. */
if (!target_can_async_p ())
mark_infrun_async_event_handler ();
}