.

zloadrace.py

@@ -25,14 +25,20 @@ There is no load vs invalidation race on NEO but the protection is implicit:
 - client app maintains .last_tid which is updated by poller thread upon
   receiving invalidations.
 - when load() is called without specifing @head (the case we are considering),
-  it uses .last_tid for @at with which to ask storage node.
+  it uses .last_tid for @at with which to ask a storage node.
 - even if client.load() observes .last_tid which was updated for simultaneously
-  committed transaction and not yet invalidated cache the following happens:
+  committed transaction with not yet invalidated cache, the following happens:
 
   * client sends AskObject packet to a storage node.
-  * ask _locks_ corresponding connection to the storage. XXX _not_ to master from which we should have received invalidation message !
-
-- client.app.load
+  * when the answer arrives it has to be picked by client poller thread.
+  * the poller thread won't proceed to that packet until the function that modified .last_tid finishes
+  * that function (neo/client/handlers/master.py invalidateObjects()) is also
+    invalidating NEO cache _and_ calls ZODB.DB.invalidate()
+  * ZODB.DB.invalidate calls ZODB.Connection.invalidate which sets
+    zconn._txn_time and zconn._invalidated
+  * even when storage-level load completes with newer than @head serial,
+    ZODB.Connection.setstate checks for oid in its ._invalidated, sees its
+    there, and retries the load with before=._txn_time
 
 
 XXX load vs invalidation race is there on ZODB4 and ZODB3, but on ZODB5 there is
@@ -68,14 +74,8 @@ def main():
 
     # two ZODB client storage connections to the same server
     zstor1 = tdb.getZODBStorage()   ; defer(zstor1.close)
-    zstor2 = tdb.getZODBStorage()   ; defer(zstor2.close)
-
     db1 = DB(zstor1)
-    db2 = DB(zstor2)
-
     zstor1.app.poll_thread.name = 'C1.poll'
-    zstor2.app.poll_thread.name = 'C2.poll'
-
 
     # XXX doc
     def init():
@@ -89,6 +89,14 @@ def main():
         transaction.commit()
         zconn.close()
 
+    init()
+
+
+    zstor2 = tdb.getZODBStorage()   ; defer(zstor2.close)
+    db2 = DB(zstor2)
+    zstor2.app.poll_thread.name = 'C2.poll'
+
+
 
     c2ready = chan()        # c1 <- c2  "I'm ready to commit"
     c2start = chan()        # c1 -> c2  "go on to commit"
@@ -176,7 +184,7 @@ def main():
 
 
 
-    init()
+    #init()
     import time
     time.sleep(2)
     print()