Prevent concurrent executions of the feed generator

xslt/feedgen.xsl

@@ -78,6 +78,14 @@ function log {
 }
 
 [ -z "$DIR" ] && DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
+if [ -e "$DIR/.itsb-feedgen" ]; then
+  echo "The lockfile at $DIR/.itsb-feedgen already exists."
+  exit 1
+fi
+log Creating lockfile at "$DIR/.itsb-feedgen"
+touch "$DIR/.itsb-feedgen"
+trap "rm -f \"$DIR/.itsb-feedgen\"" EXIT INT TERM
+
 log Building to $DIR/feeds
 mkdir -p $DIR/feeds
 
@@ -98,6 +106,8 @@ fi
     <xsl:text>
 </xsl:text>
     <xsl:apply-templates select="//itsb:feed[not(itsb:link)]" />
+    <xsl:text><![CDATA[
+rm "$DIR/.itsb-feedgen"]]></xsl:text>
   </xsl:template>
 
   <xsl:template match="itsb:feed[not(itsb:link)]">