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, 17 insertions, 0 deletions

diff --git a/src/sysdep.c b/src/sysdep.c
index 3d2b9bdeeee..96c9e538409 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -765,6 +765,23 @@ unblock_child_signal (sigset_t const *oldset)
   pthread_sigmask (SIG_SETMASK, oldset, 0);
 }
 
+/* Block SIGINT.  */
+void
+block_interrupt_signal (sigset_t *oldset)
+{
+  sigset_t blocked;
+  sigemptyset (&blocked);
+  sigaddset (&blocked, SIGINT);
+  pthread_sigmask (SIG_BLOCK, &blocked, oldset);
+}
+
+/* Restore previously saved signal mask.  */
+void
+restore_signal_mask (sigset_t const *oldset)
+{
+  pthread_sigmask (SIG_SETMASK, oldset, 0);
+}
+
 #endif  /* !MSDOS */
 
 /* Saving and restoring the process group of Emacs's terminal.  */