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author | Pedro Alves <palves@redhat.com> | 2016-04-12 16:49:30 +0100 |
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committer | Pedro Alves <palves@redhat.com> | 2016-04-12 16:54:03 +0100 |
commit | f0881b37b6734328118a5683e1e18f65a8987c89 (patch) | |
tree | 107155131f2b8453e41bf9d6b83d116523585956 /gdb/defs.h | |
parent | 5cc3ce8b5fffa7413557b7e071d8471ae6e2fc88 (diff) | |
download | binutils-f0881b37b6734328118a5683e1e18f65a8987c89.zip binutils-f0881b37b6734328118a5683e1e18f65a8987c89.tar.gz binutils-f0881b37b6734328118a5683e1e18f65a8987c89.tar.bz2 |
Introduce interruptible_select
We have places where we call a blocking gdb_select expecting that a
Ctrl-C will unblock it. However, if the Ctrl-C is pressed just before
gdb_select, the SIGINT handler runs before gdb_select, and thus
gdb_select won't return.
For example gdb_readline_no_editing:
QUIT;
/* Wait until at least one byte of data is available. Control-C
can interrupt gdb_select, but not fgetc. */
FD_ZERO (&readfds);
FD_SET (fd, &readfds);
if (gdb_select (fd + 1, &readfds, NULL, NULL, NULL) == -1)
and stdio_file_read:
/* For the benefit of Windows, call gdb_select before reading from
the file. Wait until at least one byte of data is available.
Control-C can interrupt gdb_select, but not read. */
{
fd_set readfds;
FD_ZERO (&readfds);
FD_SET (stdio->fd, &readfds);
if (gdb_select (stdio->fd + 1, &readfds, NULL, NULL, NULL) == -1)
return -1;
}
return read (stdio->fd, buf, length_buf);
This is a race classically fixed with either the self-pipe trick, or
by blocking SIGINT and then using pselect instead of select.
Blocking SIGINT most of the time would mean that check_quit_flag (and
thus QUIT) would need to do a syscall every time it is called, which
sounds best avoided, since QUIT is called in many loops. Thus we take
the self-pipe trick route (wrapped in a serial event).
Instead of having all places that need this manually add an extra file
descriptor to the set of gdb_select's watched file descriptors, we
introduce a wrapper, interruptible_select, that does that.
The Windows version of gdb_select actually does not suffer from this,
because mingw-hdep.c:gdb_call_async_signal_handler sets a Windows
event that gdb_select always waits on. So this patch can be seen as
generalization of that technique. We can't remove that extra event
from mingw-hdep.c until we get rid of immediate_quit though.
gdb/ChangeLog:
2016-04-12 Pedro Alves <palves@redhat.com>
* defs.h: Extend QUIT-related comments to mention
interruptible_select.
(quit_serial_event_set, quit_serial_event_clear): Declare.
* event-top.c: Include "ser-event.h" and "gdb_select.h".
(quit_serial_event): New global.
(async_init_signals): Make quit_serial_event.
(quit_serial_event_set, quit_serial_event_clear)
(quit_serial_event_fd, interruptible_select): New functions.
* extension.c (set_quit_flag): Set the quit serial event.
(check_quit_flag): Clear the quit serial event.
* gdb_select.h (interruptible_select): New declaration.
* guile/scm-ports.c (ioscm_input_waiting): Use
interruptible_select instead of gdb_select.
* top.c (gdb_readline_no_editing): Likewise.
* ui-file.c (stdio_file_read): Likewise.
Diffstat (limited to 'gdb/defs.h')
-rw-r--r-- | gdb/defs.h | 11 |
1 files changed, 11 insertions, 0 deletions
@@ -131,6 +131,11 @@ extern char *debug_file_directory; take a long time, and which ought to be interruptible, checks this flag using the QUIT macro. + In addition to setting a flag, the SIGINT handler also marks a + select/poll-able file descriptor as read-ready. That is used by + interruptible_select in order to support interrupting blocking I/O + in a race-free manner. + These functions use the extension_language_ops API to allow extension language(s) and GDB SIGINT handling to coexist seamlessly. */ @@ -159,6 +164,12 @@ extern void maybe_quit (void); connection. */ #define QUIT maybe_quit () +/* Set the serial event associated with the quit flag. */ +extern void quit_serial_event_set (void); + +/* Clear the serial event associated with the quit flag. */ +extern void quit_serial_event_clear (void); + /* * Languages represented in the symbol table and elsewhere. This should probably be in language.h, but since enum's can't be forward declared to satisfy opaque references before their |