Improve the readability of the code that handles SIGTTOU.

docs/NEWS.md

@@ -3,6 +3,7 @@
  * fix: complete set of German translations supplied by Hartmut Goebel ([#98](https://codeberg.org/a-j-wood/pv/pulls/98))
  * cleanup: removed TODO.md, since it's just an outdated copy of the issue tracker
  * cleanup: re-ordered structure members to reduce padding
+ * cleanup: improved readability of SIGTTOU handling code
 
 ### 1.8.14 - 7 September 2024
 

src/include/pv-internal.h

@@ -160,8 +160,7 @@ struct pvstate_s {
 		volatile sig_atomic_t rxusr2;	 /* whether SIGUSR2 was received */
 		volatile pid_t sender;		 /* PID of sending process for SIGUSR2 */
 #endif
-		int old_stderr;		 /* see pv_sig_ttou() */
-		bool pv_tty_tostop_added;	 /* whether we had to set TOSTOP on the terminal */
+		int old_stderr;			 /* see pv_sig_ttou() */
 	} signal;
 
 	/*******************
@@ -171,6 +170,7 @@ struct pvstate_s {
 		volatile sig_atomic_t reparse_display;	 /* whether to re-check format string */
 		volatile sig_atomic_t terminal_resized;	 /* whether we need to get term size again */
 		volatile sig_atomic_t trigger_exit;	 /* whether we need to abort right now */
+		volatile sig_atomic_t clear_tty_tostop_on_exit;	/* whether to clear tty TOSTOP on exit */
 	} flag;
 
 	/*****************

src/pv/cursor.c

@@ -437,8 +437,8 @@ void pv_crs_init(pvstate_t state)
 	 * If we have already set the terminal TOSTOP attribute, set the
 	 * flag in shared memory to let the other instances know.
 	 */
-	if ((!state->cursor.noipc) && state->signal.pv_tty_tostop_added && (NULL != state->cursor.shared)) {
-		debug("%s", "propagating local pv_tty_tostop_added true value to shared flag");
+	if ((!state->cursor.noipc) && (1 == state->flag.clear_tty_tostop_on_exit) && (NULL != state->cursor.shared)) {
+		debug("%s", "propagating local clear_tty_tostop_on_exit true value to shared tty_tostop_added flag");
 		state->cursor.shared->tty_tostop_added = true;
 	}
 
@@ -674,9 +674,9 @@ void pv_crs_fini(pvstate_t state)
 	 * it.
 	 */
 	if ((!state->cursor.noipc) && (NULL != state->cursor.shared) && state->cursor.shared->tty_tostop_added) {
-		if (!state->signal.pv_tty_tostop_added) {
-			debug("%s", "propagating shared tty_tostop_added true value to local flag");
-			state->signal.pv_tty_tostop_added = true;
+		if (0 == state->flag.clear_tty_tostop_on_exit) {
+			debug("%s", "propagating shared tty_tostop_added true value to local clear_tty_tostop_on_exit flag");
+			state->flag.clear_tty_tostop_on_exit = 1;
 		}
 	}
 

src/pv/signal.c

@@ -27,8 +27,13 @@ void pv_crs_needreinit(pvstate_t);
 
 /*
  * Ensure that terminal attribute TOSTOP is set.  If we have to set it,
- * record that fact by setting the state boolean "pv_tty_tostop_added" to
- * true, so that in pv_sig_fini() we can turn it back off again.
+ * record that fact by setting "clear_tty_tostop_on_exit" to 1, so that in
+ * pv_sig_fini() we can turn it back off again.
+ *
+ * In "-c" mode with IPC, then if we have to set TOSTOP, we also tell the
+ * other PV instances about it via the shared "tty_tostop_added" flag, so
+ * those instances can set their own on-exit flag, meaning that if any of
+ * the PV instances set it, the last one to exit will clear it.
  */
 static void pv_sig_ensure_tty_tostop()
 {
@@ -45,7 +50,7 @@ static void pv_sig_ensure_tty_tostop()
 	if (0 == (terminal_attributes.c_lflag & TOSTOP)) {
 		terminal_attributes.c_lflag |= TOSTOP;
 		if (0 == tcsetattr(STDERR_FILENO, TCSANOW, &terminal_attributes)) {
-			pv_sig_state->signal.pv_tty_tostop_added = true;
+			pv_sig_state->flag.clear_tty_tostop_on_exit = 1;
 			debug("%s", "set terminal TOSTOP attribute");
 		} else {
 			debug("%s: %s", "failed to set terminal TOSTOP attribute", strerror(errno));
@@ -416,7 +421,7 @@ void pv_sig_fini( /*@unused@ */  __attribute__((unused)) pvstate_t state)
 #endif
 	(void) sigaction(SIGALRM, &(pv_sig_state->signal.old_sigalrm), NULL);
 
-	need_to_clear_tostop = pv_sig_state->signal.pv_tty_tostop_added;
+	need_to_clear_tostop = 1 == pv_sig_state->flag.clear_tty_tostop_on_exit ? true : false;
 
 	if (pv_sig_state->control.cursor) {
 #ifdef HAVE_IPC
@@ -457,7 +462,7 @@ void pv_sig_fini( /*@unused@ */  __attribute__((unused)) pvstate_t state)
 			}
 		}
 
-		pv_sig_state->signal.pv_tty_tostop_added = false;
+		pv_sig_state->flag.clear_tty_tostop_on_exit = 0;
 	}
 }