Add performance profiler function

Usable anywhere that the global daemon "config" parameter can be passed
in (e.g. pvcapid/helper.py, pvcnoded/Daemon.py, etc.). Stores results in
a subdirectory of the PVC logdir called "profiler" if this directory can
be created, or prints results.

The debug config parameter ensures that the profiler can be added to
functions and not run unless the server is explicitly in debug mode.
Might not be useful as I don't initially plan to add this to every
function (only when investigating performance problems), but this
flexibility allows that to change later.

daemon-common/common.py

@@ -30,6 +30,59 @@ from re import split as re_split
 from distutils.util import strtobool
 from threading import Thread
 from shlex import split as shlex_split
+from functools import wraps
+
+
+###############################################################################
+# Performance Profiler decorator
+###############################################################################
+
+# Get performance statistics on a function or class
+class Profiler(object):
+    def __init__(self, config):
+        self.is_debug = config['debug']
+        self.pvc_logdir = '/var/log/pvc'
+
+    def __call__(self, function):
+        if not callable(function):
+            return
+
+        if not self.is_debug:
+            return function
+
+        @wraps(function)
+        def profiler_wrapper(*args, **kwargs):
+            import cProfile
+            import pstats
+            from os import path, makedirs
+            from datetime import datetime
+
+            if not path.exists(self.pvc_logdir):
+                print('Profiler: Requested profiling of {} but no log dir present; printing instead.'.format(str(function.__name__)))
+                log_result = False
+            else:
+                log_result = True
+                profiler_logdir = '{}/profiler'.format(self.pvc_logdir)
+                if not path.exists(profiler_logdir):
+                    makedirs(profiler_logdir)
+
+            pr = cProfile.Profile()
+            pr.enable()
+
+            ret = function(*args, **kwargs)
+
+            pr.disable()
+            stats = pstats.Stats(pr)
+            stats.sort_stats(pstats.SortKey.TIME)
+
+            if log_result:
+                stats.dump_stats(filename='{}/{}_{}.log'.format(profiler_logdir, str(function.__name__), str(datetime.now()).replace(' ', '_')))
+            else:
+                print('Profiler stats for function {} at {}:'.format(str(function.__name__), str(datetime.now())))
+                stats.print_stats()
+
+            return ret
+        return profiler_wrapper
 
 
 ###############################################################################