virtualx.eclass: Let Xvfb figure out the free DISPLAY

Replace the antiquated search mechanism for a free DISPLAY with Xvfb's
-displayfd option that makes Xvfb choose one itself and print it to
given fd.

Bug: https://bugs.gentoo.org/494244
Signed-off-by: Michał Górny <mgorny@gentoo.org>

1 files changed, 20 insertions, 42 deletions

diff --git a/eclass/virtualx.eclass b/eclass/virtualx.eclass
index d1c05e20b246..c0af095e89a5 100644
--- a/eclass/virtualx.eclass
+++ b/eclass/virtualx.eclass
@@ -108,65 +108,43 @@ virtx() {
 	local i=0
 	local retval=0
 	local OLD_SANDBOX_ON="${SANDBOX_ON}"
-	local XDISPLAY
 	local xvfbargs=( -screen 0 1280x1024x24 +extension RANDR )
 
 	debug-print "${FUNCNAME}: running Xvfb hack"
 	export XAUTHORITY=
-	# The following is derived from Mandrake's hack to allow
-	# compiling without the X display
-
-	einfo "Scanning for an open DISPLAY to start Xvfb ..."
-	# If we are in a chrooted environment, and there is already a
-	# X server started outside of the chroot, Xvfb will fail to start
-	# on the same display (most cases this is :0 ), so make sure
-	# Xvfb is started, else bump the display number
-	#
-	# Azarah - 5 May 2002
-	# GNOME GDM may have started X on DISPLAY :0 with a
-	# lock file /tmp/.X1024-lock, therefore start the search at 1.
-	# Else a leftover /tmp/.X1-lock will prevent finding an available display.
-	XDISPLAY=$(i=1; while [[ -f /tmp/.X${i}-lock ]] ; do ((i++));done; echo ${i})
-	debug-print "${FUNCNAME}: XDISPLAY=${XDISPLAY}"
+
+	einfo "Starting Xvfb ..."
 
 	# We really do not want SANDBOX enabled here
 	export SANDBOX_ON="0"
 
-	debug-print "${FUNCNAME}: Xvfb :${XDISPLAY} ${xvfbargs[*]}"
-	Xvfb :${XDISPLAY} "${xvfbargs[@]}" &>/dev/null &
-	sleep 2
-
-	local start=${XDISPLAY}
-	while [[ ! -f /tmp/.X${XDISPLAY}-lock ]]; do
-		# Stop trying after 15 tries
-		if ((XDISPLAY - start > 15)) ; then
-			eerror "'Xvfb :${XDISPLAY} ${xvfbargs[*]}' returns:"
-			echo
-			Xvfb :${XDISPLAY} "${xvfbargs[@]}"
-			echo
-			eerror "If possible, correct the above error and try your emerge again."
-			die "Unable to start Xvfb"
-		fi
-			((XDISPLAY++))
-		debug-print "${FUNCNAME}: Xvfb :${XDISPLAY} ${xvfbargs[*]}"
-		Xvfb :${XDISPLAY} "${xvfbargs[@]}" &>/dev/null &
-		sleep 2
-	done
+	debug-print "${FUNCNAME}: Xvfb -displayfd 1 ${xvfbargs[*]}"
+	local logfile=${T}/Xvfb.log
+	local pidfile=${T}/Xvfb.pid
+	# NB: bash command substitution blocks until Xvfb prints fd to stdout
+	# and then closes the fd; only then it backgrounds properly
+	export DISPLAY=:$(
+		Xvfb -displayfd 1 "${xvfbargs[@]}" 2>"${logfile}" &
+		echo "$!" > "${pidfile}"
+	)
+
+	if [[ ${DISPLAY} == : ]]; then
+		eerror "Xvfb failed to start, reprinting error log"
+		cat "${logfile}"
+		die "Xvfb failed to start"
+	fi
 
 	# Now enable SANDBOX again if needed.
 	export SANDBOX_ON="${OLD_SANDBOX_ON}"
 
-	einfo "Starting Xvfb on \$DISPLAY=${XDISPLAY} ..."
-
-	export DISPLAY=:${XDISPLAY}
-	# Do not break on error, but setup $retval, as we need
-	# to kill Xvfb
+	# Do not break on error, but setup $retval, as we need to kill Xvfb
+	einfo "Xvfb started on DISPLAY=${DISPLAY}"
 	debug-print "${FUNCNAME}: $@"
 	nonfatal "$@"
 	retval=$?
 
 	# Now kill Xvfb
-	kill $(cat /tmp/.X${XDISPLAY}-lock)
+	kill "$(<"${pidfile}")"
 
 	# die if our command failed
 	[[ ${retval} -ne 0 ]] && die "Failed to run '$@'"