Use common functions to handle file locking

 * lib/common.sh: implement
   - lock_open_write()
   - lock_open_read()
   - lock_close()
 * archbuild.in, makechrootpkg.in, mkarchroot.in: use said functions

This has two benefits:
 1. All programs using these methods gain the ability to inherit locks,
    something that only mkarchroot could do before.  This allows the
    commands to be more compos-able.
 2. It is more readable. File locking isn't obvious.

1 files changed, 49 insertions, 0 deletions

diff --git a/lib/common.sh b/lib/common.sh
index b39bbbc..5204091 100644
--- a/lib/common.sh
+++ b/lib/common.sh
@@ -104,6 +104,55 @@ in_array() {
 }
 
 ##
+#  usage : lock_open_write( $fd, $path, $wait_message )
+##
+lock_open_write() {
+	local fd=$1
+	local path=$2
+	local msg=$3
+
+	# Only reopen the FD if it wasn't handed to us
+	if [[ $(readlink -f /dev/fd/$fd) != "${path}.lock" ]]; then
+		eval "exec $fd>${path}.lock"
+	fi
+
+	if ! flock -n $fd; then
+		stat_busy "$msg"
+		flock $fd
+		stat_done
+	fi
+}
+
+##
+#  usage : lock_open_read( $fd, $path, $wait_message )
+##
+lock_open_read() {
+	local fd=$1
+	local path=$2
+	local msg=$3
+
+	# Only reopen the FD if it wasn't handed to us
+	if [[ $(readlink -f /dev/fd/$fd) != "${path}.lock" ]]; then
+		eval "exec $fd>${path}.lock"
+	fi
+
+	if ! flock -sn $fd; then
+		stat_busy "$msg"
+		flock -s $fd
+		stat_done
+	fi
+}
+
+
+##
+#  usage : lock_close( $fd )
+##
+lock_close() {
+	local fd=$1
+	eval "exec $fd>&-"
+}
+
+##
 #  usage : get_full_version( [$pkgname] )
 # return : full version spec, including epoch (if necessary), pkgver, pkgrel
 ##