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Fix gdb.mi/mi-nsmoribund.exp timeouts

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The PPC64 buildbot has been showing timeouts in mi-nsmoribund.exp,
like this:

 (...)
 -thread-info
 FAIL: gdb.mi/mi-nsmoribund.exp: thread state: all running except the breakpoint thread (timeout)

... and I can reproduce this on gcc110 (PPC64) on the gcc compile
farm.

That is, the test sends "-thread-info" to GDB, but GDB never replies
back.

The problem is that these machines are too fast for gdb.  :-)

That test has a few threads running the same tight loop, and
constantly hitting a thread-specific breakpoint that needs to be
stepped over.  If threads trip on breakpoints fast enough that
linux-nat.c's event pipe associated with SIGCHLD is constantly being
written to, even if the stdin file descriptor also has an event to
handle, gdb never gets to it. because linux-nat.c's pipe comes first
in the set of descriptors served by the poll/select code in the event
loop.

Fix this by having the event loop serve file event sources in
round-robin-like fashion, similarly to how its done in
gdb_do_one_event.

Unfortunately, the poll and the select variants each need their own
fixing.

Tested on x86_64 Fedora 20 (poll and select variants), and PPC64
Fedora 18.  Fixes the timeout in the PPC64 machine in the compile farm
that times out without this, and I won't be surprised if it fixes
other random timeouts in other tests.

(gdbserver's copy of the event-loop doesn't need this (yet), as it
still pushes all ready events to an event queue.  That is, it hasn't
had 70b66289 merged yet.  We should really merge both event-loop.c
copies into a single shared file, but that's for another day.)

gdb/ChangeLog:
2015-05-15  Pedro Alves  <palves@redhat.com>
	    Simon Marchi  <simon.marchi@ericsson.com>

	* event-loop.c (gdb_notifier) <next_file_handler,
	next_poll_fds_index>: New fields.
	(get_next_file_handler_to_handle_and_advance): New function.
	(delete_file_handler): If deleting the next file handler to
	handle, advance to the next file handler.
	(gdb_wait_for_event): Bail early if no event fired.  Poll file
	handlers in round-robin fashion.
This commit is contained in:
Pedro Alves 2015-05-15 16:26:53 +01:00
parent 452003ef2c
commit 4e63d0ac89
2 changed files with 100 additions and 33 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
gdb/ChangeLog
View File

@ -1,3 +1,14 @@
2015-05-15 Pedro Alves <palves@redhat.com>
Simon Marchi <simon.marchi@ericsson.com>
* event-loop.c (gdb_notifier) <next_file_handler,
next_poll_fds_index>: New fields.
(get_next_file_handler_to_handle_and_advance): New function.
(delete_file_handler): If deleting the next file handler to
handle, advance to the next file handler.
(gdb_wait_for_event): Bail early if no event fired. Poll file
handlers in round-robin fashion.
2015-05-15 Pedro Alves <palves@redhat.com>
* linux-tdep.c (linux_find_memory_regions_full): Rename local

122
gdb/event-loop.c
View File

@ -165,10 +165,24 @@ static struct
/* Ptr to head of file handler list. */
file_handler *first_file_handler;
/* Next file handler to handle, for the select variant. To level
the fairness across event sources, we serve file handlers in a
round-robin-like fashion. The number and order of the polled
file handlers may change between invocations, but this is good
enough. */
file_handler *next_file_handler;
#ifdef HAVE_POLL
/* Ptr to array of pollfd structures. */
struct pollfd *poll_fds;
/* Next file descriptor to handle, for the poll variant. To level
the fairness across event sources, we poll the file descriptors
in a round-robin-like fashion. The number and order of the
polled file descriptors may change between invocations, but
this is good enough. */
int next_poll_fds_index;
/* Timeout in milliseconds for calls to poll(). */
int poll_timeout;
#endif
@ -494,6 +508,31 @@ create_file_handler (int fd, int mask, handler_func * proc,
file_ptr->mask = mask;
}
/* Return the next file handler to handle, and advance to the next
file handler, wrapping around if the end of the list is
reached. */
static file_handler *
get_next_file_handler_to_handle_and_advance (void)
{
file_handler *curr_next;
/* The first time around, this is still NULL. */
if (gdb_notifier.next_file_handler == NULL)
gdb_notifier.next_file_handler = gdb_notifier.first_file_handler;
curr_next = gdb_notifier.next_file_handler;
gdb_assert (curr_next != NULL);
/* Advance. */
gdb_notifier.next_file_handler = curr_next->next_file;
/* Wrap around, if necessary. */
if (gdb_notifier.next_file_handler == NULL)
gdb_notifier.next_file_handler = gdb_notifier.first_file_handler;
return curr_next;
}
/* Remove the file descriptor FD from the list of monitored fd's:
i.e. we don't care anymore about events on the FD. */
void
@ -576,6 +615,17 @@ delete_file_handler (int fd)
file_ptr->mask = 0;
/* If this file handler was going to be the next one to be handled,
advance to the next's next, if any. */
if (gdb_notifier.next_file_handler == file_ptr)
{
if (file_ptr->next_file == NULL
&& file_ptr == gdb_notifier.first_file_handler)
gdb_notifier.next_file_handler = NULL;
else
get_next_file_handler_to_handle_and_advance ();
}
/* Get rid of the file handler in the file handler list. */
if (file_ptr == gdb_notifier.first_file_handler)
gdb_notifier.first_file_handler = file_ptr->next_file;
@ -672,7 +722,6 @@ gdb_wait_for_event (int block)
{
file_handler *file_ptr;
int num_found = 0;
int i;
/* Make sure all output is done before getting another event. */
gdb_flush (gdb_stdout);
@ -743,37 +792,47 @@ gdb_wait_for_event (int block)
}
}
/* Avoid looking at poll_fds[i]->revents if no event fired. */
if (num_found <= 0)
return 0;
/* Run event handlers. We always run just one handler and go back
to polling, in case a handler changes the notifier list. Since
events for sources we haven't consumed yet wake poll/select
immediately, no event is lost. */
/* To level the fairness across event descriptors, we handle them in
a round-robin-like fashion. The number and order of descriptors
may change between invocations, but this is good enough. */
if (use_poll)
{
#ifdef HAVE_POLL
for (i = 0; (i < gdb_notifier.num_fds) && (num_found > 0); i++)
int i;
int mask;
while (1)
{
if (gdb_notifier.next_poll_fds_index >= gdb_notifier.num_fds)
gdb_notifier.next_poll_fds_index = 0;
i = gdb_notifier.next_poll_fds_index++;
gdb_assert (i < gdb_notifier.num_fds);
if ((gdb_notifier.poll_fds + i)->revents)
num_found--;
else
continue;
for (file_ptr = gdb_notifier.first_file_handler;
file_ptr != NULL;
file_ptr = file_ptr->next_file)
{
if (file_ptr->fd == (gdb_notifier.poll_fds + i)->fd)
break;
}
if (file_ptr)
{
int mask = (gdb_notifier.poll_fds + i)->revents;
handle_file_event (file_ptr, mask);
return 1;
}
break;
}
for (file_ptr = gdb_notifier.first_file_handler;
file_ptr != NULL;
file_ptr = file_ptr->next_file)
{
if (file_ptr->fd == (gdb_notifier.poll_fds + i)->fd)
break;
}
gdb_assert (file_ptr != NULL);
mask = (gdb_notifier.poll_fds + i)->revents;
handle_file_event (file_ptr, mask);
return 1;
#else
internal_error (__FILE__, __LINE__,
_("use_poll without HAVE_POLL"));
@ -781,11 +840,12 @@ gdb_wait_for_event (int block)
}
else
{
for (file_ptr = gdb_notifier.first_file_handler;
(file_ptr != NULL) && (num_found > 0);
file_ptr = file_ptr->next_file)
/* See comment about even source fairness above. */
int mask = 0;
do
{
int mask = 0;
file_ptr = get_next_file_handler_to_handle_and_advance ();
if (FD_ISSET (file_ptr->fd, &gdb_notifier.ready_masks[0]))
mask |= GDB_READABLE;
@ -793,15 +853,11 @@ gdb_wait_for_event (int block)
mask |= GDB_WRITABLE;
if (FD_ISSET (file_ptr->fd, &gdb_notifier.ready_masks[2]))
mask |= GDB_EXCEPTION;
if (!mask)
continue;
else
num_found--;
handle_file_event (file_ptr, mask);
return 1;
}
while (mask == 0);
handle_file_event (file_ptr, mask);
return 1;
}
return 0;
}