sfeed_update: add variable for max amount of feeds to update concurrently

This adds a variable for the maximum amount of feeds to update concurrently. A
system/user may have fork resource limits or want to setup some job limit.

Thanks leot for the idea and feedback!

sfeed_update

@@ -5,6 +5,10 @@
 # defaults
 sfeedpath="$HOME/.sfeed/feeds"
 
+# used for processing feeds concurrently: wait until ${maxjobs} amount of
+# feeds are finished at a time.
+maxjobs=8
+
 # load config (evaluate shellscript).
 # loadconfig(configfile)
 loadconfig() {
@@ -71,6 +75,11 @@ fetchfeed() {
 # fetch and parse feed.
 # feed(name, feedurl, [basesiteurl], [encoding])
 feed() {
+	# wait until ${maxjobs} are finished: throughput using this logic is
+	# non-optimal, but it is simple and portable.
+	test $((curjobs % maxjobs)) -eq 0 && wait
+	curjobs=$((curjobs + 1))
+
 	(name="$1"
 	filename="$(printf '%s' "$1" | tr '/' '_')"
 	feedurl="$2"
@@ -122,6 +131,8 @@ feeds() {
 	echo "See sfeedrc.example for an example." >&2
 }
 
+# job counter.
+curjobs=0
 # kill whole current process group on ^C (SIGINT).
 isinterrupted="0"
 # SIGTERM: signal to terminate parent.