webmap-import: add option --lockfile to obtain an exclusive lock.

This avoids starting multiple imports in parallel.  Some layers, such as
Skogsstyrelsen's, are quite large and filtering/importing causes rather
high load.

1 files changed, 10 insertions, 0 deletions

diff --git a/webmap-import b/webmap-import
index 37826cf..bfee9dc 100755
--- a/webmap-import
+++ b/webmap-import
@@ -18,7 +18,9 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 #----------------------------------------------------------------------
 
+from os import O_WRONLY, O_CREAT, O_TRUNC, O_CLOEXEC
 import os
+from fcntl import flock, LOCK_EX
 import logging
 import argparse
 import tempfile
@@ -1193,6 +1195,8 @@ if __name__ == '__main__':
         help=f'cache directory (default: {os.curdir})')
     parser.add_argument('--debug', action='count', default=0,
         help=argparse.SUPPRESS)
+    parser.add_argument('--lockfile', default=None,
+        help=f'obtain an exclusive lock before starting unpacking and importing')
     parser.add_argument('groupname', nargs='*', help='group layer name(s) to process')
     args = parser.parse_args()
 
@@ -1244,6 +1248,12 @@ if __name__ == '__main__':
     srs = getSRS(common.config.get('SRS', None))
     extent = getExtent(common.config.get('extent', None), srs=srs)
 
+    if args.lockfile is not None:
+        # obtain an exclusive lock and don't release it until exiting the program
+        lock_fd = os.open(args.lockfile, O_WRONLY|O_CREAT|O_TRUNC|O_CLOEXEC, mode=0o644)
+        logging.debug('flock("%s", LOCK_EX)', args.lockfile)
+        flock(lock_fd, LOCK_EX)
+
     cachedir = Path(args.cachedir) if args.cachedir is not None else None
     rv = 0
     for layername, layerdef in layers.items():