Add an interface to register clearCache callbacks in roundupdb.

Sometimes complicated computations may require an application cache.
This application can now register a callback to clear the application
cache, because roundup knows better when to clear it (usually when a
transaction ends, either with rollback or with commit). The interface
for this is currently considered experimental. The current interface
is registerClearCacheCallback(self, method, param) where method is
called with param as the only parameter.

Author: schlatterbeck

CHANGES.txt

@@ -7,7 +7,14 @@ Entries without name were done by Richard Jones.
 
 Features:
 
-- ...
+- Add an interface to register clearCache callbacks in roundupdb.
+  Sometimes complicated computations may require an application cache.
+  This application can now register a callback to clear the application
+  cache, because roundup knows better when to clear it (usually when a
+  transaction ends, either with rollback or with commit). The interface
+  for this is currently considered experimental. The current interface
+  is registerClearCacheCallback(self, method, param) where method is
+  called with param as the only parameter.  (Ralf Schlatterbeck)
 
 Fixed:
 

roundup/backends/back_anydbm.py

@@ -733,6 +733,8 @@ def clearCache(self):
         self.newnodes = {}
         self.destroyednodes = {}
         self.transactions = []
+        # upcall is necessary!
+        roundupdb.Database.clearCache(self)
 
     def getCachedClassDB(self, classname):
         """ get the class db, looking in our cache of databases for commit

roundup/backends/rdbms_common.py

@@ -195,6 +195,8 @@ def __init__(self, config, journaltag=None):
     def clearCache(self):
         self.cache = {}
         self.cache_lru = []
+        # upcall is necessary!
+        roundupdb.Database.clearCache(self)
 
     def getSessionManager(self):
         return Sessions(self)

roundup/roundupdb.py

@@ -149,6 +149,26 @@ def get_logger(self):
 
         return self.__logger
 
+    def clearCache(self):
+        """ Backends may keep a cache.
+            It must be cleared at end of commit and rollback methods.
+            We allow to register user-defined cache-clearing routines
+            that are called by this routine.
+        """
+        if getattr (self, 'cache_callbacks', None) :
+            for method, param in self.cache_callbacks:
+                method(param)
+
+    def registerClearCacheCallback(self, method, param = None):
+        """ Register a callback method for clearing the cache.
+            It is called with the given param as the only parameter.
+            Even if the parameter is not specified, the method has to
+            accept a single parameter.
+        """
+        if not getattr (self, 'cache_callbacks', None) :
+            self.cache_callbacks = []
+        self.cache_callbacks.append ((method, param))
+
 
 class DetectorError(RuntimeError):
     """ Raised by detectors that want to indicate that something's amiss