From c310d29fc4fa37d6f3e1e49a063c50d36b20b62a Mon Sep 17 00:00:00 2001
From: Nathaniel Graff <nathaniel.graff@sifive.com>
Date: Thu, 23 Jan 2020 13:48:15 -0800
Subject: [PATCH] Remove bound on parser memoization cache

Improve parser performance by removing bound on the memoization cache

Adds the environment variable option PYDEVICETREE_CACHE_SIZE_BOUND which
can be used to limit the memoization cache if necessary.

Signed-off-by: Nathaniel Graff <nathaniel.graff@sifive.com>
---
 .github/workflows/tests.yml    |  3 +++
 Makefile                       |  5 +++++
 pydevicetree/source/grammar.py | 16 ++++++++++++++--
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 004e6af..8701889 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -32,6 +32,9 @@ jobs:
       - name: Run unit tests
         run:
           make test-unit
+      - name: Run unit tests with bounded parser cache
+        run:
+          make test-cache-size-bound
       - name: Run integration tests
         run:
           make test-integration
diff --git a/Makefile b/Makefile
index 7d9a39e..74676ca 100644
--- a/Makefile
+++ b/Makefile
@@ -47,6 +47,11 @@ test-unit: venv/bin/activate $(UNIT_TESTS)
 	. $< && python3 -m unittest $(UNIT_TESTS)
 test: test-unit
 
+.PHONY: test-cache-size-bound
+test-cache-size-bound: venv/bin/activate $(UNIT_TESTS)
+	PYDEVICETREE_CACHE_SIZE_BOUND=128 . $< && python3 -m unittest $(UNIT_TESTS)
+test: test-cache-size-bound
+
 INTEGRATION_TESTS = tests/test_full_trees.py
 
 .PHONY: test-integration
diff --git a/pydevicetree/source/grammar.py b/pydevicetree/source/grammar.py
index 7768439..cabf917 100644
--- a/pydevicetree/source/grammar.py
+++ b/pydevicetree/source/grammar.py
@@ -2,9 +2,22 @@
 # Copyright (c) 2019 SiFive Inc.
 # SPDX-License-Identifier: Apache-2.0
 
+import os
+import sys
+
 import pyparsing as p # type: ignore
 
-p.ParserElement.enablePackrat()
+ENV_CACHE_OPTION = "PYDEVICETREE_CACHE_SIZE_BOUND"
+
+cache_bound = None
+if ENV_CACHE_OPTION in os.environ:
+    option = os.environ[ENV_CACHE_OPTION]
+    if option != "None":
+        try:
+            cache_bound = int(option)
+        except ValueError:
+            print("%s requires a valid integer" % ENV_CACHE_OPTION, file=sys.stderr)
+p.ParserElement.enablePackrat(cache_bound)
 
 node_name = p.Word(p.alphanums + ",.-+_") ^ p.Literal("/")
 integer = p.pyparsing_common.integer ^ (p.Literal("0x").suppress() + p.pyparsing_common.hex_integer)
@@ -59,6 +72,5 @@
 devicetree.ignore("//" + p.SkipTo(p.lineEnd))
 
 if __name__ == "__main__":
-    import sys
     if len(sys.argv) > 1:
         devicetree.parseFile(sys.argv[1]).pprint()