From b48224e514d375aa8e317118b35993c0d46adf2f Mon Sep 17 00:00:00 2001
From: Giles Atkinson <“gatk555@gmail.com”>
Date: Mon, 4 Nov 2024 19:15:29 +0000
Subject: [PATCH] Improve the behaviour of ngspice when run in the background
 on a Unix-like OS with job control.  The progress ticker is suppressed for a
 command like "ngspice some_circuit.cir &" so the terminal remains usuable
 while the simulation runs.

---
 src/frontend/outitf.c         | 10 +++++-----
 src/frontend/signal_handler.c | 29 ++++++++++++++++++++++++-----
 src/frontend/signal_handler.h |  1 +
 src/main.c                    |  4 +++-
 4 files changed, 33 insertions(+), 11 deletions(-)

diff --git a/src/frontend/outitf.c b/src/frontend/outitf.c
index 35bb0d1ca..87329841d 100644
--- a/src/frontend/outitf.c
+++ b/src/frontend/outitf.c
@@ -635,7 +635,7 @@ OUTpData(runDesc *plotPtr, IFvalue *refValue, IFvalue *valuePtr)
                     every quarter of a second, to give some feedback without using
                     too much CPU time  */
 #ifndef HAS_WINGUI
-                if (!orflag && !ft_norefprint) {
+                if (!orflag && !ft_norefprint && !cp_background) {
                     currclock = clock();
                     if ((currclock-lastclock) > (0.25*CLOCKS_PER_SEC)) {
                         fprintf(stdout, " Reference value : % 12.5e\r",
@@ -649,7 +649,7 @@ OUTpData(runDesc *plotPtr, IFvalue *refValue, IFvalue *valuePtr)
             else { /* And the same for a non-complex (real) value  */
                 fileAddRealValue(run->fp, run->binary, refValue->rValue);
 #ifndef HAS_WINGUI
-                if (!orflag && !ft_norefprint) {
+                if (!orflag && !ft_norefprint && !cp_background) {
                     currclock = clock();
                     if ((currclock-lastclock) > (0.25*CLOCKS_PER_SEC)) {
                         fprintf(stdout, " Reference value : % 12.5e\r",
@@ -744,7 +744,7 @@ OUTpData(runDesc *plotPtr, IFvalue *refValue, IFvalue *valuePtr)
             variable just the same  */
 
 #ifndef HAS_WINGUI
-        if (!orflag && !ft_norefprint) {
+        if (!orflag && !ft_norefprint && !cp_background) {
             currclock = clock();
             if ((currclock-lastclock) > (0.25*CLOCKS_PER_SEC)) {
                 if (run->isComplex) {
@@ -1532,7 +1532,7 @@ InterpFileAdd(runDesc *run, IFvalue *refValue, IFvalue *valuePtr)
             interpolatenow = FALSE;
         }
 #ifndef HAS_WINGUI
-        if (!orflag && !ft_norefprint) {
+        if (!orflag && !ft_norefprint && !cp_background) {
             currclock = clock();
             if ((currclock-lastclock) > (0.25*CLOCKS_PER_SEC)) {
                 fprintf(stdout, " Reference value : % 12.5e\r",
@@ -1693,7 +1693,7 @@ InterpPlotAdd(runDesc *run, IFvalue *refValue, IFvalue *valuePtr)
 #endif
 
 #ifndef HAS_WINGUI
-    if (!orflag && !ft_norefprint) {
+    if (!orflag && !ft_norefprint && !cp_background) {
         currclock = clock();
         if ((currclock-lastclock) > (0.25*CLOCKS_PER_SEC)) {
             fprintf(stdout, " Reference value : % 12.5e\r",
diff --git a/src/frontend/signal_handler.c b/src/frontend/signal_handler.c
index 4d4d6ec2c..581a3d16e 100644
--- a/src/frontend/signal_handler.c
+++ b/src/frontend/signal_handler.c
@@ -2,7 +2,6 @@
 Copyright 1990 Regents of the University of California.  All rights reserved.
 Author: 1985 Wayne A. Christopher, U. C. Berkeley CAD Group
 **********/
-
 /*
  * The signal routines for spice 3 and nutmeg.
  */
@@ -18,6 +17,10 @@ Author: 1985 Wayne A. Christopher, U. C. Berkeley CAD Group
 #include "signal_handler.h"
 #include "plotting/graf.h"
 
+#ifdef SIGTTIN
+#include <unistd.h>
+#endif
+
 #ifdef HAS_WINGUI
 void winmessage(char* new_msg);
 #endif
@@ -138,6 +141,23 @@ sigttio(void)
         (void) kill(getpid(), SIGTSTP); /* This should stop us */
     }
 }
+
+/* Is this a background process? */
+
+void test_background(void)
+{
+    pid_t terminal_group;
+    int   tty;
+
+    tty = open("/dev/tty", O_RDONLY);
+    if (tty < 0) {
+        cp_background = TRUE; // No controlling terminal, so "in background".
+        return;
+    }
+    terminal_group = tcgetpgrp(tty); // Posix 2001, so portable.
+    close(tty);
+    cp_background = (terminal_group != getpgrp());
+}
 #endif
 
 /* This should give a new prompt if cshpar is waiting for input.  */
@@ -148,10 +168,8 @@ void
 sigstop(void)
 {
     gr_clean();
-    if (!cp_background) {
-        (void) signal(SIGTSTP, SIG_DFL);
-        (void) kill(getpid(), SIGTSTP); /* This should stop us */
-    }
+    (void) signal(SIGTSTP, SIG_DFL);
+    (void) kill(getpid(), SIGTSTP); /* This should stop us */
 }
 
 
@@ -159,6 +177,7 @@ void
 sigcont(void)
 {
     (void) signal(SIGTSTP, (SIGNAL_FUNCTION) sigstop);
+    test_background();
     if (cp_cwait)
         LONGJMP(jbuf, 1);
 }
diff --git a/src/frontend/signal_handler.h b/src/frontend/signal_handler.h
index 66168d818..611de12de 100644
--- a/src/frontend/signal_handler.h
+++ b/src/frontend/signal_handler.h
@@ -16,6 +16,7 @@ void sigbus(void);
 void sigsegv(void);
 void sigsegvsh(void);
 void sig_sys(void);
+void test_background(void);
 
 extern JMP_BUF jbuf;
 
diff --git a/src/main.c b/src/main.c
index 698637cbb..6367b06ac 100644
--- a/src/main.c
+++ b/src/main.c
@@ -704,7 +704,7 @@ app_rl_readlines(void)
 
             cp_cwait = TRUE;
             app_event_func(); // Direct call to process X11 input.
-        }
+        } else
 #endif
         cp_cwait = TRUE;
         line = readline(cp_background ? NULL : prompt());
@@ -1213,10 +1213,12 @@ int main(int argc, char **argv)
 
 #ifdef SIGTSTP
         signal(SIGTSTP, (SIGNAL_FUNCTION) sigstop);
+        signal(SIGCONT, (SIGNAL_FUNCTION) sigcont);
 #endif
 #ifdef SIGTTIN
         signal(SIGTTIN, (SIGNAL_FUNCTION) sigttio);
         signal(SIGTTOU, (SIGNAL_FUNCTION) sigttio);
+        test_background(); // Process started in the background?
 #endif
     }