LocalTracChanges: cachingpermstore.py

from trac.core import TracError
from trac.perm import DefaultPermissionStore

try: 
    import threading 
except ImportError: 
    import dummy_threading as threading 

class UsersWithPermCachingPermissionStore(DefaultPermissionStore):
    """
    Extension to the Default implementation that caches the get_users_with_permissions() function
    """

    _cached_users = {} 
    _cache_lock = threading.Lock() 

    def get_users_with_permissions(self, permissions):

        cache_key = "".join(sorted(permissions))

        #We check once before locking and once after to prevent locking when we don't need to
        if (not self._cached_users.has_key(cache_key)):
            self._cache_lock.acquire()
            try: 
                if (not self._cached_users.has_key(cache_key)):
                    self.log.info("Generating Permissions Cache for '%s'" % (cache_key))
                    self._cached_users[cache_key] = DefaultPermissionStore.get_users_with_permissions(self, permissions)
            finally: 
                self._cache_lock.release() 

        return self._cached_users[cache_key]

    def grant_permission(self, username, action):
        self._cache_lock.acquire()
        try:
            self.log.info("Clearing Permissions Cache")
            self._cached_users.clear()
            DefaultPermissionStore.grant_permission(self, username, action)
        finally: 
            self._cache_lock.release() 

    def revoke_permission(self, username, action):
        self._cache_lock.acquire()
        try: 
            self.log.info("Clearing Permissions Cache")
            self._cached_users.clear()
            DefaultPermissionStore.revoke_permission(self, username, action)
        finally: 
            self._cache_lock.release()