feat: file-backed cache for heatmap

app/config.py

@@ -5,4 +5,5 @@
 STACK_DIR = 'examples'
 HOST = '0.0.0.0'
 PORT = 5000
-JSONIFY_PRETTYPRINT_REGULAR = False
+USE_HEATMAP_FILECACHE = True
+JSONIFY_PRETTYPRINT_REGULAR = False

app/util/heatmap.py

@@ -21,7 +21,8 @@
 import os
 import gzip
 import collections
-from os.path import abspath, join
+import json
+from os.path import abspath, join, isfile, dirname, basename
 from math import ceil, floor
 from flask import abort
 
@@ -59,6 +60,11 @@ def read_offsets(filename):
             # use cached heatmap
             return heatmap_cache[path]
 
+    if config.USE_HEATMAP_FILECACHE and avail_heatmap_filecache(path):
+        fc = read_heatmap_filecache(path)
+        if fc.mtime == mtime:
+            return fc.heatmap
+
     # read .gz files via a "gunzip -c" pipe
     if filename.endswith(".gz"):
         try:
@@ -109,8 +115,33 @@ def read_offsets(filename):
     heatmap = collections.namedtuple('offsets', ['start', 'end', 'offsets'])(start, end, offsets)
     heatmap_cache[path] = heatmap
     heatmap_mtimes[path] = mtime
+    if config.USE_HEATMAP_FILECACHE:
+        write_heatmap_filecache(path, heatmap, mtime)
     return heatmap
 
+def convert_path_to_filecache(path):
+    return dirname(path) + '/.' + basename(path) + '-heatmap-cache'
+
+
+def write_heatmap_filecache(path, heatmap, mtime):
+    f = open(convert_path_to_filecache(path), 'wt')
+    f.write(json.dumps({'start': heatmap.start, 'end': heatmap.end, 'offsets': heatmap.offsets, 'mtime': mtime}))
+    f.close()
+
+
+def read_heatmap_filecache(path):
+    f = open(convert_path_to_filecache(path), 'rt')
+    h = json.loads(f.read())
+    f.close()
+    return collections.namedtuple('cache', ['heatmap', 'mtime'])(
+            collections.namedtuple('offsets', ['start', 'end', 'offsets'])(h['start'], h['end'], h['offsets']),
+            h['mtime']
+            )
+
+def avail_heatmap_filecache(path):
+    filename = convert_path_to_filecache(path)
+    return isfile(filename)
+
 # return a heatmap from the cached offsets
 def generate_heatmap(filename, rows=None):
     o = read_offsets(filename)