Fix an egregious bug that caused caches to fail when run with an

optimized Python. :(

src/ZEO/cache.py

@@ -39,19 +39,19 @@ from ZODB.utils import p64, u64, z64
 logger = logging.getLogger("ZEO.cache")
 
 # A disk-based cache for ZEO clients.
-# 
+#
 # This class provides an interface to a persistent, disk-based cache
 # used by ZEO clients to store copies of database records from the
 # server.
-# 
+#
 # The details of the constructor as unspecified at this point.
-# 
+#
 # Each entry in the cache is valid for a particular range of transaction
 # ids.  The lower bound is the transaction that wrote the data.  The
 # upper bound is the next transaction that wrote a revision of the
 # object.  If the data is current, the upper bound is stored as None;
 # the data is considered current until an invalidate() call is made.
-# 
+#
 # It is an error to call store() twice with the same object without an
 # intervening invalidate() to set the upper bound on the first cache
 # entry.  Perhaps it will be necessary to have a call the removes
@@ -59,12 +59,12 @@ logger = logging.getLogger("ZEO.cache")
 # entry.
 
 # Cache verification
-# 
+#
 # When the client is connected to the server, it receives
 # invalidations every time an object is modified.  When the client is
 # disconnected then reconnects, it must perform cache verification to make
 # sure its cached data is synchronized with the storage's current state.
-# 
+#
 # quick verification
 # full verification
 #
@@ -206,7 +206,7 @@ class ClientCache(object):
             self.f = tempfile.TemporaryFile()
             self.f.write(magic+z64)
             logger.info("created temporary cache file %r", self.f.name)
-            
+
         self._initfile(fsize)
 
         # Statistics:  _n_adds, _n_added_bytes,
@@ -328,7 +328,7 @@ class ClientCache(object):
                 seek(block_size-5, 1)
             sync(self.f)
 
-            # There is always data to read and 
+            # There is always data to read and
             assert last and status in ' f1234'
             first_free_offset = last
         else:
@@ -358,7 +358,7 @@ class ClientCache(object):
         except KeyError:
             logger.error("Couldn't find non-current %r", (oid, tid))
 
-            
+
     def clearStats(self):
         self._n_adds = self._n_added_bytes = 0
         self._n_evicts = self._n_evicted_bytes = 0
@@ -471,7 +471,8 @@ class ClientCache(object):
             return None
         self.f.seek(ofs)
         read = self.f.read
-        assert read(1) == 'a', (ofs, self.f.tell(), oid)
+        status = read(1)
+        assert status == 'a', (ofs, self.f.tell(), oid)
         size, saved_oid, tid, end_tid, lver, ldata = unpack(
             ">I8s8s8sHI", read(34))
         assert saved_oid == oid, (ofs, self.f.tell(), oid, saved_oid)
@@ -479,7 +480,10 @@ class ClientCache(object):
 
         data = read(ldata)
         assert len(data) == ldata, (ofs, self.f.tell(), oid, len(data), ldata)
-        assert read(8) == oid, (ofs, self.f.tell(), oid) 
+
+        # WARNING: The following assert changes the file position.
+        # We must not depend on ths below or we'll fail in optimized mode.
+        assert read(8) == oid, (ofs, self.f.tell(), oid)
 
         self._n_accesses += 1
         self._trace(0x22, oid, tid, end_tid, ldata)
@@ -507,7 +511,8 @@ class ClientCache(object):
 
         self.f.seek(ofs)
         read = self.f.read
-        assert read(1) == 'a', (ofs, self.f.tell(), oid, before_tid)
+        status = read(1)
+        assert status == 'a', (ofs, self.f.tell(), oid, before_tid)
         size, saved_oid, saved_tid, end_tid, lver, ldata = unpack(
             ">I8s8s8sHI", read(34))
         assert saved_oid == oid, (ofs, self.f.tell(), oid, saved_oid)
@@ -516,12 +521,15 @@ class ClientCache(object):
         assert lver == 0, "Versions aren't supported"
         data = read(ldata)
         assert len(data) == ldata, (ofs, self.f.tell())
+
+        # WARNING: The following assert changes the file position.
+        # We must not depend on ths below or we'll fail in optimized mode.
         assert read(8) == oid, (ofs, self.f.tell(), oid)
-        
+
         if end_tid < before_tid:
             self._trace(0x24, oid, "", before_tid)
             return None
-            
+
         self._n_accesses += 1
         self._trace(0x26, oid, "", saved_tid)
         return data, saved_tid, end_tid
@@ -543,7 +551,8 @@ class ClientCache(object):
             if ofs:
                 seek(ofs)
                 read = self.f.read
-                assert read(1) == 'a', (ofs, self.f.tell(), oid)
+                status = read(1)
+                assert status == 'a', (ofs, self.f.tell(), oid)
                 size, saved_oid, saved_tid, end_tid = unpack(
                     ">I8s8s8s", read(28))
                 assert saved_oid == oid, (ofs, self.f.tell(), oid, saved_oid)
@@ -613,7 +622,7 @@ class ClientCache(object):
         else:
             self.current[oid] = ofs
             self._trace(0x52, oid, start_tid, dlen=len(data))
-            
+
         self.currentofs += size
 
     ##
@@ -635,7 +644,7 @@ class ClientCache(object):
     #       to threading issues, that when applying a local
     #       invalidation after a store, that later invalidations from
     #       the server may already have arrived.
-    
+
     @locked
     def invalidate(self, oid, tid, server_invalidation=True):
         if tid is not None:
@@ -655,7 +664,8 @@ class ClientCache(object):
 
         self.f.seek(ofs)
         read = self.f.read
-        assert read(1) == 'a', (ofs, self.f.tell(), oid)
+        status = read(1)
+        assert status == 'a', (ofs, self.f.tell(), oid)
         size, saved_oid, saved_tid, end_tid = unpack(">I8s8s8s", read(28))
         assert saved_oid == oid, (ofs, self.f.tell(), oid, saved_oid)
         assert end_tid == z64, (ofs, self.f.tell(), oid)
@@ -685,7 +695,8 @@ class ClientCache(object):
             self._lock.acquire()
             try:
                 seek(ofs)
-                assert read(1) == 'a', (ofs, self.f.tell(), oid)
+                status = read(1)
+                assert status == 'a', (ofs, self.f.tell(), oid)
                 size, saved_oid, tid, end_tid = unpack(">I8s8s8s", read(28))
                 assert saved_oid == oid, (ofs, self.f.tell(), oid, saved_oid)
                 assert end_tid == z64, (ofs, self.f.tell(), oid)
@@ -750,7 +761,7 @@ class ClientCache(object):
             except:
                 print `tid`, `end_tid`
                 raise
-                
+
         self._trace = _trace
         _trace(0x00)