sx: further tuning the signal situation

This commit removes the complication of trying to handle client PIDs as
doing so didn't provide any noticable gain.  The main issue was that
both `wait' commands didn't wait on their respective PIDs while the
final cleanup wasn't called with both client and server PIDs and so
the server remained running due to -noreset.

The exit status of `sx' should again reflect that of the Xorg's
which may be useful for scripts.

Also slightly improves the comments on how Xorg handles USR1 signals.

Fixes https://github.com/Earnestly/sx/issues/19

sx

@@ -3,18 +3,19 @@
 # requires xauth Xorg /dev/urandom
 
 cleanup() {
-    for pid; do
+    if kill -0 "$pid" 2> /dev/null; then
-        if kill -0 "$pid" 2> /dev/null; then
+        kill "$pid"
-            kill "$pid"
+        wait "$pid"
-            wait "$pid"
+        xorg=$?
-        fi
+    fi
-    done
 
     if ! stty "$stty"; then
         stty sane
     fi
 
     xauth remove :"$tty"
+
+    exit "${xorg:-0}"
 }
 
 stty=$(stty -g)
@@ -30,21 +31,17 @@ touch -- "$XAUTHORITY"
 
 xauth add :"$tty" MIT-MAGIC-COOKIE-1 "$(od -An -N16 -tx /dev/urandom | tr -d ' ')"
 
-for signal in HUP INT TERM; do
+for signal in HUP INT TERM QUIT; do
-    # The client variable is set by the USR1 signal trap and contains the
+    trap 'cleanup; trap - "$signal"; kill -s "$signal" "$$"' "$signal"
-    # client's PID.
-    # shellcheck disable=SC2154
-    trap 'cleanup "$client" "$server"; trap - "$signal"; kill -s "$signal" "$$"' "$signal"
 done
-trap cleanup EXIT
 
-# Xorg will check if its USR1 disposition is SIG_IGN and use this state to
+# Xorg will check whether it inherited a USR1 with a disposition of SIG_IGN and
-# reply back to the parent process with a SIGUSR1 of its own as indication it
+# use this state to reply back to the parent process with its own USR1.
-# is ready to accept connections.
+# This is done to indicate that the server is ready to accept connections.
 # Taking advantage of this feature allows launching the client directly from a
 # USR1 signal trap which obviates the need to poll for server readiness.
-trap 'DISPLAY=:$tty "${@:-$cfgdir/sxrc}" & client=$!; wait' USR1
+trap 'DISPLAY=:$tty exec "${@:-$cfgdir/sxrc}" & wait "$!"' USR1
 
-(trap '' USR1 && exec Xorg :"$tty" -keeptty vt"$tty" -noreset -auth "$XAUTHORITY") &
+(trap '' USR1 && exec Xorg :"$tty" -keeptty vt"$tty" -noreset -auth "$XAUTHORITY") & pid=$!
-server=$!
+wait "$pid"
-wait
+cleanup

sx.1

@@ -1,4 +1,4 @@
-.TH SX 1 "6 February 2019" 2.1.1
+.TH SX 1 "6 October 2020" 2.1.6
 .SH NAME
 sx \- start an xorg server
 .SH SYNOPSIS
@@ -10,7 +10,9 @@ can be used to replace both
 .BR xinit (1)
 and
 .BR startx (1)
-for starting an Xorg server with an initial client.  By default
+for starting an
+.BR Xorg (1)
+server with an initial client.  By default
 .B sx
 will attempt to execute
 .I \%XDG_CONFIG_HOME/sx/sxrc
@@ -20,6 +22,11 @@ is provided.  The
 .I command
 may have additional
 .IR arguments .
+.SH EXIT STATUS
+.B sx
+will attempt to inherit the exit status from the
+.BR Xorg (1)
+server.  Otherwise it is 0.
 .SH ENVIRONMENT
 .TP
 .B XAUTHORITY
@@ -75,7 +82,7 @@ Use an existing
 .I .Xinitrc
 by specifying an appropriate interpreter such as
 .BR sh (1)
-or marking it executable with a correct interpreter line:
+or making it executable with a correct interpreter line:
 .IP
 .EX
 .B sx sh ~/.Xinitrc