[tools] Incrementally keep track of GC NVP output

We not keep track of the histogram as we process values and do not wait until
printing the histogram. Furthermore processing the histogram is not O(n) for n
values.

BUG=

Review URL: https://codereview.chromium.org/1364733002

Cr-Commit-Position: refs/heads/master@{#30891}

tools/eval_gc_nvp.py

@@ -6,39 +6,57 @@
 
 """This script is used to analyze GCTracer's NVP output."""
 
+
 from argparse import ArgumentParser
+from copy import deepcopy
 from gc_nvp_common import split_nvp
 from sys import stdin
 
+
 class Histogram:
-  def __init__(self, values, granularity):
-    self.values = list(values)  # copy over values
+  def __init__(self, granularity, fill_empty):
     self.granularity = granularity
+    self.histogram = {}
+    self.fill_empty = fill_empty
+
+  def add(self, key):
+    index = int(key / self.granularity)
+    if index not in self.histogram:
+      self.histogram[index] = 0
+    self.histogram[index] += 1
 
   def __str__(self):
     ret = []
-    values = list(self.values)  # copy over values
-    min_value = 0
-    while len(values) > 0:
-      max_value = min_value +  self.granularity
-      sub = [x for x in self.values if x >= min_value and x < max_value]
+    keys = self.histogram.keys()
+    keys.sort()
+    last = -self.granularity
+    for key in keys:
+      min_value = key * self.granularity
+      max_value = min_value + self.granularity
+
+      if self.fill_empty:
+        while (last + self.granularity) != min_value:
+          last += self.granularity
+          ret.append("  [{0},{1}[: {2}".format(
+            str(last), str(last + self.granularity), 0))
+
       ret.append("  [{0},{1}[: {2}".format(
-        str(min_value), str(max_value),len(sub)))
-      min_value += self.granularity
-      values = [x for x in values if x not in sub]
+        str(min_value), str(max_value), self.histogram[key]))
+      last = min_value
     return "\n".join(ret)
 
 
 class Category:
-  def __init__(self, key, histogram, granularity):
+  def __init__(self, key, histogram):
     self.key = key
     self.values = []
     self.histogram = histogram
-    self.granularity = granularity
 
   def process_entry(self, entry):
     if self.key in entry:
       self.values.append(float(entry[self.key]))
+      if self.histogram:
+        self.histogram.add(float(entry[self.key]))
 
   def __str__(self):
     ret = [self.key]
@@ -48,7 +66,7 @@ class Category:
       ret.append("  max: {0}".format(max(self.values)))
       ret.append("  avg: {0}".format(sum(self.values) / len(self.values)))
       if self.histogram:
-        ret.append(str(Histogram(self.values, self.granularity)))
+        ret.append(str(self.histogram))
     return "\n".join(ret)
 
 
@@ -59,6 +77,9 @@ def main():
   parser.add_argument('--histogram-granularity', metavar='GRANULARITY',
                       type=int, nargs='?', default=5,
                       help='histogram granularity (default: 5)')
+  parser.add_argument('--no-histogram-print-empty', dest='histogram_print_empty',
+                      action='store_false',
+                      help='print empty histogram buckets')
   feature_parser = parser.add_mutually_exclusive_group(required=False)
   feature_parser.add_argument('--histogram', dest='histogram',
                               action='store_true',
@@ -67,9 +88,14 @@ def main():
                               action='store_false',
                               help='do not print histogram')
   parser.set_defaults(histogram=True)
+  parser.set_defaults(histogram_print_empty=True)
   args = parser.parse_args()
 
-  categories = [ Category(key, args.histogram, args.histogram_granularity)
+  histogram = None
+  if args.histogram:
+    histogram = Histogram(args.histogram_granularity, args.histogram_print_empty)
+
+  categories = [ Category(key, deepcopy(histogram))
                  for key in args.keys ]
 
   while True: