compile_pkgs: use flock to not colide in git mirrors

This locks git mirror directory when we are updating mirrors. This
should solve race condition with multiple builds failing to update
mirrors and failing that way completely.

Only update is protected. The expectation is that initialization is
happenning only once and is protected by non-existence of directory. If
there is going to be problem with initialization as well then we can add
locking as well.

compile_pkgs

@@ -215,30 +215,31 @@ configure() {
 available_commands+=( ["update_mirror"]="Updates all local mirrors" )
 update_mirror() {
 	[ -n "$GIT_MIRROR" ] || return 0
+	[ -d "$GIT_MIRROR" ] || return 0
 	[ -z "$mirror_updated" ] || return 0
 
 	_report "Updating local mirrors"
-	mkdir -p "$GIT_MIRROR"
-	pushd "$GIT_MIRROR"
-	if [ ! -d openwrt ]; then
-		git clone --mirror "$OPENWRT_URL" openwrt
-	fi
-	OPENWRT_URL="$GIT_MIRROR/openwrt"
-	for mirror in ./*; do
-		cd "$mirror" || continue
-		if ! git remote update --prune; then
-			sleep $(( 1 + RANDOM % 30 ))
+	flock --exclusive "$GIT_MIRROR" "$SHELL" -s "$GIT_MIRROR" <<"EOF"
+		cd "$1"
+		for mirror in ./*; do
+			[ -d "$mirror" ] || continue
+			cd "$mirror"
 			git remote update --prune
-		fi
-		cd "$GIT_MIRROR"
-	done
-	popd
+			cd "$1"
+		done
+EOF
 	mirror_updated="yes"
 }
 
 _checkout_init() {
 	_report "Checking out clean OpenWRT repository"
 	update_mirror
+	if [ -n "$GIT_MIRROR" ]; then
+		mkdir -p "$GIT_MIRROR"
+		[ -d "$GIT_MIRROR/openwrt" ] || \
+			git clone --mirror "$OPENWRT_URL" "$GIT_MIRROR/openwrt"
+		OPENWRT_URL="$GIT_MIRROR/openwrt"
+	fi
 	rm -rf .git
 	git init
 	git remote add origin "$OPENWRT_URL"