[dvs] Add generic polling utility (#1233)

Signed-off-by: Danny Allen <daall@microsoft.com>

tests/dvslib/dvs_common.py

@@ -0,0 +1,59 @@
+"""
+    dvs_common contains common infrastructure for writing tests for the
+    virtual switch.
+"""
+
+import collections
+import time
+
+_PollingConfig = collections.namedtuple('PollingConfig', 'polling_interval timeout strict')
+
+class PollingConfig(_PollingConfig):
+    """
+        PollingConfig provides parameters that are used to control the behavior
+        for polling functions.
+
+        Params:
+            polling_interval (int): How often to poll, in seconds.
+            timeout (int): The maximum amount of time to wait, in seconds.
+            strict (bool): If the strict flag is set, reaching the timeout
+                will cause tests to fail (e.g. assert False)
+    """
+
+    pass
+
+def wait_for_result(polling_function, polling_config):
+    """
+        wait_for_result will periodically run `polling_function`
+        using the parameters described in `polling_config` and return the
+        output of the polling function.
+
+        Args:
+            polling_config (PollingConfig): The parameters to use to poll
+                the db.
+            polling_function (Callable[[], (bool, Any)]): The function being
+                polled. The function takes no arguments and must return a
+                status which indicates if the function was succesful or
+                not, as well as some return value.
+
+        Returns:
+            Any: The output of the polling function, if it is succesful,
+            None otherwise.
+    """
+    if polling_config.polling_interval == 0:
+        iterations = 1
+    else:
+        iterations = int(polling_config.timeout // polling_config.polling_interval) + 1
+
+    for _ in range(iterations):
+        (status, result) = polling_function()
+
+        if status:
+            return result
+
+        time.sleep(polling_config.polling_interval)
+
+    if polling_config.strict:
+        assert False
+
+    return None

tests/dvslib/dvs_database.py

@@ -2,21 +2,8 @@
     dvs_database contains utilities for interacting with redis when writing
     tests for the virtual switch.
 """
-from __future__ import print_function
-
-import time
-import collections
-
 from swsscommon import swsscommon
-
-
-# PollingConfig provides parameters that are used to control polling behavior
-# when accessing redis:
-# - polling_interval: how often to check for updates in redis
-# - timeout: the max amount of time to wait for updates in redis
-# - strict: if the strict flag is set, failure to receive updates will cause
-#           the polling method to cause tests to fail (e.g. assert False)
-PollingConfig = collections.namedtuple('PollingConfig', 'polling_interval timeout strict')
+from dvslib.dvs_common import wait_for_result, PollingConfig
 
 
 class DVSDatabase(object):
@@ -56,27 +43,27 @@ def create_entry(self, table_name, key, entry):
         formatted_entry = swsscommon.FieldValuePairs(entry.items())
         table.set(key, formatted_entry)
 
-    def wait_for_entry(self, table_name, key,
-                       polling_config=DEFAULT_POLLING_CONFIG):
+    def get_entry(self, table_name, key):
         """
-            Gets the entry stored at `key` in the specified table. This method
-            will wait for the entry to exist.
+            Gets the entry stored at `key` in the specified table.
 
             Args:
                 table_name (str): The name of the table where the entry is
                     stored.
                 key (str): The key that maps to the entry being retrieved.
-                polling_config (PollingConfig): The parameters to use to poll
-                    the db.
 
             Returns:
                 Dict[str, str]: The entry stored at `key`. If no entry is found,
                 then an empty Dict will be returned.
-
         """
 
-        access_function = self._get_entry_access_function(table_name, key, True)
-        return self._db_poll(polling_config, access_function)
+        table = swsscommon.Table(self.db_connection, table_name)
+        (status, fv_pairs) = table.get(key)
+
+        if not status:
+            return {}
+
+        return dict(fv_pairs)
 
     def delete_entry(self, table_name, key):
         """
@@ -91,6 +78,49 @@ def delete_entry(self, table_name, key):
         table = swsscommon.Table(self.db_connection, table_name)
         table._del(key)  # pylint: disable=protected-access
 
+    def get_keys(self, table_name):
+        """
+            Gets all of the keys stored in the specified table.
+
+            Args:
+                table_name (str): The name of the table from which to fetch
+                the keys.
+
+            Returns:
+                List[str]: The keys stored in the table. If no keys are found,
+                then an empty List will be returned.
+        """
+
+        table = swsscommon.Table(self.db_connection, table_name)
+        keys = table.getKeys()
+
+        return keys if keys else []
+
+    def wait_for_entry(self, table_name, key,
+                       polling_config=DEFAULT_POLLING_CONFIG):
+        """
+            Gets the entry stored at `key` in the specified table. This method
+            will wait for the entry to exist.
+
+            Args:
+                table_name (str): The name of the table where the entry is
+                    stored.
+                key (str): The key that maps to the entry being retrieved.
+                polling_config (PollingConfig): The parameters to use to poll
+                    the db.
+
+            Returns:
+                Dict[str, str]: The entry stored at `key`. If no entry is found,
+                then an empty Dict will be returned.
+
+        """
+
+        def _access_function():
+            fv_pairs = self.get_entry(table_name, key)
+            return (bool(fv_pairs), fv_pairs)
+
+        return wait_for_result(_access_function, polling_config)
+
     def wait_for_empty_entry(self,
                              table_name,
                              key,
@@ -109,8 +139,11 @@ def wait_for_empty_entry(self,
                 bool: True if no entry exists at `key`, False otherwise.
         """
 
-        access_function = self._get_entry_access_function(table_name, key, False)
-        return not self._db_poll(polling_config, access_function)
+        def _access_function():
+            fv_pairs = self.get_entry(table_name, key)
+            return (not fv_pairs, fv_pairs)
+
+        return wait_for_result(_access_function, polling_config)
 
     def wait_for_n_keys(self,
                         table_name,
@@ -133,122 +166,8 @@ def wait_for_n_keys(self,
                 then an empty List will be returned.
         """
 
-        access_function = self._get_keys_access_function(table_name, num_keys)
-        return self._db_poll(polling_config, access_function)
-
-    def _get_keys_access_function(self, table_name, num_keys):
-        """
-            Generates an access function to check for `num_keys` in the given
-            table and return the list of keys if successful.
-
-            Args:
-                table_name (str): The name of the table from which to fetch
-                    the keys.
-                num_keys (int): The number of keys to check for in the table.
-                    If this is set to None, then this function will just return
-                    whatever keys are in the table.
-
-            Returns:
-                Callable([[], (bool, List[str])]): A function that can be
-                called to access the database.
-
-                If `num_keys` keys are found in the given table, or left
-                unspecified, then the function will return True along with
-                the list of keys that were found. Otherwise, the function will
-                return False and some undefined list of keys.
-        """
-
-        table = swsscommon.Table(self.db_connection, table_name)
-
-        def _accessor():
-            keys = table.getKeys()
-            if not keys:
-                keys = []
-
-            if not num_keys and num_keys != 0:
-                status = True
-            else:
-                status = len(keys) == num_keys
-
-            return (status, keys)
-
-        return _accessor
-
-    def _get_entry_access_function(self, table_name, key, expect_entry):
-        """
-            Generates an access function to check for existence of an entry
-            at `key` and return it if successful.
-
-            Args:
-                table_name (str): The name of the table from which to fetch
-                    the entry.
-                key (str): The key that maps to the entry being retrieved.
-                expect_entry (bool): Whether or not we expect to see an entry
-                    at `key`.
-
-            Returns:
-                Callable([[], (bool, Dict[str, str])]): A function that can be
-                called to access the database.
-
-                If `expect_entry` is set and an entry is found, then the
-                function will return True along with the entry that was found.
-
-                If `expect_entry` is not set and no entry is found, then the
-                function will return True along with an empty Dict.
-
-                In all other cases, the function will return False with some
-                undefined Dict.
-        """
-
-        table = swsscommon.Table(self.db_connection, table_name)
-
-        def _accessor():
-            (status, fv_pairs) = table.get(key)
-
-            status = expect_entry == status
-
-            if fv_pairs:
-                entry = dict(fv_pairs)
-            else:
-                entry = {}
-
-            return (status, entry)
-
-        return _accessor
-
-    @staticmethod
-    def _db_poll(polling_config, access_function):
-        """
-            _db_poll will periodically run `access_function` on the database
-            using the parameters described in `polling_config` and return the
-            output of the access function.
-
-            Args:
-                polling_config (PollingConfig): The parameters to use to poll
-                    the db.
-                access_function (Callable[[], (bool, Any)]): The function used
-                    for polling the db. Note that the function must return a
-                    status which indicates if the function was succesful or
-                    not, as well as some return value.
-
-            Returns:
-                Any: The output of the access function, if it is succesful,
-                None otherwise.
-        """
-        if polling_config.polling_interval == 0:
-            iterations = 1
-        else:
-            iterations = int(polling_config.timeout // polling_config.polling_interval) + 1
-
-        for _ in range(iterations):
-            (status, result) = access_function()
-
-            if status:
-                return result
-
-            time.sleep(polling_config.polling_interval)
-
-        if polling_config.strict:
-            assert False
+        def _access_function():
+            keys = self.get_keys(table_name)
+            return (len(keys) == num_keys, keys)
 
-        return None
+        return wait_for_result(_access_function, polling_config)