python: Add JsonLoader to pystats

Allows for loading JSON files (e.g. m5out/stats.json) into the gem5
Python stats model.

Change-Id: I948dff0b23ea65c4c7acaac5e4fdf3795de1c0a7
Signed-off-by: Kelly Nguyen <klynguyen@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/43606
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/python/SConscript

@@ -71,6 +71,7 @@ PySource('m5.ext.pystats', 'm5/ext/pystats/simstat.py')
 PySource('m5.ext.pystats', 'm5/ext/pystats/statistic.py')
 PySource('m5.ext.pystats', 'm5/ext/pystats/storagetype.py')
 PySource('m5.ext.pystats', 'm5/ext/pystats/timeconversion.py')
+PySource('m5.ext.pystats', 'm5/ext/pystats/jsonloader.py')
 PySource('m5.stats', 'm5/stats/gem5stats.py')
 
 Source('pybind11/core.cc', add_tags='python')

src/python/m5/ext/pystats/__init__.py

@@ -30,6 +30,7 @@ from .simstat import SimStat
 from .statistic import Statistic
 from .storagetype import StorageType
 from .timeconversion import TimeConversion
+from .jsonloader import JsonLoader
 
 __all__ = [
            "Group",
@@ -38,4 +39,5 @@ __all__ = [
            "TimeConversion",
            "StorageType",
            "JsonSerializable",
-          ]
+           "JsonLoader",
+          ]

src/python/m5/ext/pystats/jsonloader.py

@@ -0,0 +1,92 @@
+# Copyright (c) 2021 The Regents of The University of California
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met: redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer;
+# redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in the
+# documentation and/or other materials provided with the distribution;
+# neither the name of the copyright holders nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+from .simstat import SimStat
+from .statistic import Scalar, Distribution, Accumulator
+from .group import Group, Vector
+import json
+from typing import IO
+
+class JsonLoader(json.JSONDecoder):
+    """
+    Subclass of JSONDecoder that overrides 'object_hook'. Converts JSON object
+    into a SimStat object.
+
+    Usage
+    -----
+    ```
+    from m5.ext.pystats.jsonloader import JsonLoader
+
+    with open(path) as f:
+        simstat_object = json.load(f, cls=JsonLoader)
+    ```
+    """
+
+    def __init__(self):
+        json.JSONDecoder.__init__(self, object_hook=self.__json_to_simstat)
+
+    def __json_to_simstat(self, d: dict) -> SimStat:
+        if 'type' in d:
+            if d['type'] == 'Scalar':
+                d.pop('type', None)
+                return Scalar(**d)
+
+            elif d['type'] == 'Distribution':
+                d.pop('type', None)
+                return Distribution(**d)
+
+            elif d['type'] == 'Accumulator':
+                d.pop('type', None)
+                return Accumulator(**d)
+
+            elif d['type'] == 'Group':
+                return Group(**d)
+
+            elif d['type'] == 'Vector':
+                d.pop('type', None)
+                d.pop('time_conversion', None)
+                return Vector(d)
+        else:
+            return SimStat(**d)
+
+def load(json_file: IO) -> SimStat:
+    """
+    Wrapper function that provides a cleaner interface for using the
+    JsonLoader class.
+
+    Usage
+    -----
+    ```
+    import m5.ext.pystats as pystats
+
+    with open(path) as f:
+        pystats.jsonloader.load(f)
+    ```
+    """
+
+    simstat_object = json.load(json_file, cls=JsonLoader)
+    return simstat_object
+