Fix crashes upon C-g on Posix TTY frames

* src/thread.h (struct thread_state): New member not_holding_lock.
(maybe_reacquire_global_lock): Add prototype.
* src/thread.c: Include syssignal.h.
(maybe_reacquire_global_lock): New function.
(really_call_select): Set the not_holding_lock member of the
thread state before releasing the lock, and rest it after
re-acquiring the lock when the select function returns.  Block
SIGINT while doing this to make sure we are not interrupted on TTY
frames.
* src/sysdep.c (block_interrupt_signal, restore_signal_mask): New
functions.
* src/syssignal.h (block_interrupt_signal, restore_signal_mask):
Add prototypes.
* src/keyboard.c (read_char) [THREADS_ENABLED]: Call
maybe_reacquire_global_lock.  (Bug#25178)

1 files changed, 3 insertions, 0 deletions

diff --git a/src/keyboard.c b/src/keyboard.c
index 1fb1d492ce6..f2ee313b8c9 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -2571,6 +2571,9 @@ read_char (int commandflag, Lisp_Object map,
          so restore it now.  */
       restore_getcjmp (save_jump);
       pthread_sigmask (SIG_SETMASK, &empty_mask, 0);
+#if THREADS_ENABLED
+      maybe_reacquire_global_lock ();
+#endif
       unbind_to (jmpcount, Qnil);
       XSETINT (c, quit_char);
       internal_last_event_frame = selected_frame;