.

wcfs/wcfs.go

@@ -1437,6 +1437,13 @@ func (wlink *WatchLink) setupWatch(ctx context.Context, foid zodb.Oid, at zodb.T
 	// preparing and processing initial pins, also send pins for read
 	// blocks. If we don't, we can miss to send pin for a freshly read
 	// block which could have revision > w.at .	XXX test
+	//
+	//                1   3    2   4
+	//	-----.----x---o----x---x-----------------
+	//           ↑
+	//          w.at
+	//
+	//
 	// XXX locking
 	// XXX register only if watch was created anew, not updated?
 	f.watches[w] = struct{}{}
@@ -1475,6 +1482,7 @@ func (wlink *WatchLink) setupWatch(ctx context.Context, foid zodb.Oid, at zodb.T
 	}
 
 	// XXX locking
+	// XXX do at the same time when registering ^^^, so that simultaneous READs see correct w.at
 	w.at = at
 
 	wg, ctx := errgroup.WithContext(ctx)

wcfs/wcfs_test.py

@@ -893,8 +893,8 @@ class tSrvReq:
 # pins as if all blocks @head were accesses - i.e. considering all file changes
 # in (at, head] range.
 #
-# The caller has to take cached/not-cached effect into account on its own
-# (see tDB._accessed & friends)
+# The caller has to take accessed/not-accessed effect into account on its own
+# (see tDB._accessed & friends)     XXX rework?
 @func(tDB)
 def _pinAt(t, zf, at):  # -> pin = {} blk -> rev
     # XXX dup in _blkData
@@ -1418,6 +1418,8 @@ def test_wcfs():
     # XXX watch @at when file did not existed -> error
 
 
+    # XXX unpin to @head (δblk is there but not yet accessed) vs concurrent
+    # access to that blk which must pin blk (race ?)
 
 
     # XXX watch for 2 files via single wlink