avoid sqlite deadlock on windows

copyparty/u2idx.py

@@ -21,6 +21,12 @@ except:
     HAVE_SQLITE3 = False
 
 
+try:
+    from pathlib import Path
+except:
+    pass
+
+
 class U2idx(object):
     def __init__(self, conn):
         self.log_func = conn.log_func
@@ -76,7 +82,22 @@ class U2idx(object):
         if not bos.path.exists(db_path):
             return None
 
-        cur = sqlite3.connect(db_path, 2).cursor()
+        cur = None
+        if ANYWIN:
+            uri = ""
+            try:
+                uri = "{}?mode=ro&nolock=1".format(Path(db_path).as_uri())
+                cur = sqlite3.connect(uri, 2, uri=True).cursor()
+                self.log("ro: {}".format(db_path))
+            except:
+                self.log("could not open read-only: {}\n{}".format(uri, min_ex()))
+
+        if not cur:
+            # on windows, this steals the write-lock from up2k.deferred_init --
+            # seen on win 10.0.17763.2686, py 3.10.4, sqlite 3.37.2
+            cur = sqlite3.connect(db_path, 2).cursor()
+            self.log("opened {}".format(db_path))
+
         self.cur[ptop] = cur
         return cur