Python logger enhancement to support setting log level at real time

src/sonic-py-common/sonic_py_common/logger.py

@@ -26,20 +26,49 @@ class Logger(object):
     DEFAULT_LOG_FACILITY = LOG_FACILITY_USER
     DEFAULT_LOG_OPTION = LOG_OPTION_NDELAY
 
-    def __init__(self, log_identifier=None, log_facility=DEFAULT_LOG_FACILITY, log_option=DEFAULT_LOG_OPTION):
-        self._syslog = syslog
-
+    def __init__(self, log_identifier=None, log_facility=DEFAULT_LOG_FACILITY, log_option=DEFAULT_LOG_OPTION,
+                 enable_set_log_level_on_fly=False, db_name=None):
         if log_identifier is None:
             log_identifier = os.path.basename(sys.argv[0])
+        if db_name is None:
+            self.db_name = log_identifier
+        else:
+            self.db_name = db_name
+        self.enable_set_log_level_on_fly = enable_set_log_level_on_fly
 
         # Initialize syslog
-        self._syslog.openlog(ident=log_identifier, logoption=log_option, facility=log_facility)
+        syslog.openlog(ident=log_identifier, logoption=log_option, facility=log_facility)
 
-        # Set the default minimum log priority to LOG_PRIORITY_NOTICE
-        self.set_min_log_priority(self.LOG_PRIORITY_NOTICE)
+        self._logger = None
 
     def __del__(self):
-        self._syslog.closelog()
+        syslog.closelog()
+
+    @property
+    def logger(self):
+        if self._logger is None:
+            try:
+                from swsscommon.swsscommon import Logger as SwssLogger
+            except ImportError:
+                # Workaround for unit test. In some SONiC Python package, it mocked
+                # swsscommon lib for unit test purpose, but it does not contain Logger
+                # class. To make those unit test happy, here provides a MagicMock object.
+                if sys.version_info.major == 3:
+                    from unittest import mock
+                else:
+                    # Expect the 'mock' package for python 2
+                    # https://pypi.python.org/pypi/mock
+                    import mock
+                SwssLogger = mock.MagicMock()
+                instance = mock.MagicMock()
+                SwssLogger.getInstance.return_value = instance
+                instance.getMinPrio.return_value = syslog.LOG_NOTICE
+            self._logger = SwssLogger.getInstance()
+            if self.enable_set_log_level_on_fly:
+                # Performance warning: linkToDbNative will potentially create a new thread.
+                # The thread listens to CONFIG DB for log level changes.
+                self._logger.linkToDbNative(self.db_name, 'NOTICE')
+        return self._logger
 
     #
     # Methods for setting minimum log priority
@@ -53,7 +82,7 @@ def set_min_log_priority(self, priority):
         Args:
             priority: The minimum priority at which to log messages
         """
-        self._min_log_priority = priority
+        self.logger.setMinPrio(priority)
 
     def set_min_log_priority_error(self):
         """
@@ -90,9 +119,9 @@ def set_min_log_priority_debug(self):
     #
 
     def log(self, priority, msg, also_print_to_console=False):
-        if self._min_log_priority >= priority:
+        if self.logger.getMinPrio() >= priority:
             # Send message to syslog
-            self._syslog.syslog(priority, msg)
+            self.logger.write(priority, msg)
 
             # Send message to console
             if also_print_to_console:

src/sonic-py-common/tests/logger_test.py

@@ -0,0 +1,53 @@
+import sys
+
+if sys.version_info.major == 3:
+    from unittest import mock
+else:
+    # Expect the 'mock' package for python 2
+    # https://pypi.python.org/pypi/mock
+    import mock
+
+from sonic_py_common import logger
+
+
+class TestLogger:
+    def test_log(self):
+        log = logger.Logger()
+        mock_log = mock.MagicMock()
+        mock_log.write = mock.MagicMock()
+        mock_log.getMinPrio.return_value = logger.Logger.LOG_PRIORITY_DEBUG
+
+        log._logger = mock_log
+        log.set_min_log_priority(logger.Logger.LOG_PRIORITY_DEBUG)
+
+        log.log_debug('debug message')
+        mock_log.write.assert_called_with(logger.Logger.LOG_PRIORITY_DEBUG, 'debug message')
+
+        log.log_info('info message')
+        mock_log.write.assert_called_with(logger.Logger.LOG_PRIORITY_INFO, 'info message')
+
+        log.log_notice('notice message')
+        mock_log.write.assert_called_with(logger.Logger.LOG_PRIORITY_NOTICE, 'notice message')
+
+        log.log_error('error message')
+        mock_log.write.assert_called_with(logger.Logger.LOG_PRIORITY_ERROR, 'error message')
+
+        log.log_warning('warning message')
+        mock_log.write.assert_called_with(logger.Logger.LOG_PRIORITY_WARNING, 'warning message')
+
+        mock_log.getMinPrio.return_value = logger.Logger.LOG_PRIORITY_INFO
+        mock_log.write.reset_mock()
+        log.log_debug('debug message')
+        mock_log.write.assert_not_called()
+
+        log.log_info('info message', also_print_to_console=True)
+        log.log_info('info message')
+        mock_log.write.assert_called_with(logger.Logger.LOG_PRIORITY_INFO, 'info message')
+
+    def test_set_log_level(self):
+        log = logger.Logger()
+        log.set_min_log_priority_error()
+        log.set_min_log_priority_warning()
+        log.set_min_log_priority_notice()
+        log.set_min_log_priority_info()
+        log.set_min_log_priority_debug()