Use file based locking when running script locally

Fixes #18

find_posts.py

@@ -683,6 +683,17 @@ class OrderedSet:
 
 if __name__ == "__main__":
 
+    LOCK_FILE = 'artifacts/lock.lock'
+
+    if( os.path.exists(LOCK_FILE)):
+        log(f"Lock file exists at {LOCK_FILE}")
+        sys.exit(1)
+
+    with open(LOCK_FILE, "w", encoding="utf-8") as f:
+        f.write(f"{datetime.now()}")
+
+    try:
+
         SEEN_URLS_FILE = "artifacts/seen_urls"
         REPLIED_TOOT_SERVER_IDS_FILE = "artifacts/replied_toot_server_ids"
         KNOWN_FOLLOWINGS_FILE = "artifacts/known_followings"
@@ -727,3 +738,9 @@ if __name__ == "__main__":
 
         with open(REPLIED_TOOT_SERVER_IDS_FILE, "w", encoding="utf-8") as f:
             json.dump(dict(list(REPLIED_TOOT_SERVER_IDS.items())[-10000:]), f)
+
+        os.remove(LOCK_FILE)
+
+    except Exception as ex:
+        os.remove(LOCK_FILE)
+        raise