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authorPedro Alves <palves@redhat.com>2016-04-12 16:49:30 +0100
committerPedro Alves <palves@redhat.com>2016-04-12 16:54:03 +0100
commitf0881b37b6734328118a5683e1e18f65a8987c89 (patch)
tree107155131f2b8453e41bf9d6b83d116523585956 /gdb/gdb_select.h
parent5cc3ce8b5fffa7413557b7e071d8471ae6e2fc88 (diff)
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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/gdb_select.h')
-rw-r--r--gdb/gdb_select.h15
1 files changed, 15 insertions, 0 deletions
diff --git a/gdb/gdb_select.h b/gdb/gdb_select.h
index e00a332..d346c60 100644
--- a/gdb/gdb_select.h
+++ b/gdb/gdb_select.h
@@ -33,4 +33,19 @@
extern int gdb_select (int n, fd_set *readfds, fd_set *writefds,
fd_set *exceptfds, struct timeval *timeout);
+/* Convenience wrapper around gdb_select that returns -1/EINTR if
+ set_quit_flag is set, either on entry or from a signal handler or
+ from a different thread while select is blocked. The quit flag is
+ not cleared on exit -- the caller is responsible to check it with
+ check_quit_flag or QUIT.
+
+ Note this does NOT return -1/EINTR if any signal handler other than
+ SIGINT runs, nor if the current SIGINT handler does not call
+ set_quit_flag. */
+extern int interruptible_select (int n,
+ fd_set *readfds,
+ fd_set *writefds,
+ fd_set *exceptfds,
+ struct timeval *timeout);
+
#endif /* !defined(GDB_SELECT_H) */