[tools/perf]: Atomically move results of trace2html, and fix a bug

If pinpoint_traces.py is interrupted while html2trace is busy, the next
extraction would take partial results. To make the process robust in
presence of interruptions, create a temporary directory for html2trace,
then atomically rename it to the directory that will be searched on
extraction.

The operation may seem not equivalent to creating a '.tmp.json' and
renaming it, because this is indeed not equivalent. This change fixes
the bug that I missed in previous testing when I forgot to delete the
json_cache, hence this code was not executing. This time json_cache was
deleted before testing.

Bug: 1119406
Change-Id: I7cfb19572a9ffa26827dd113bb92b2253b0a2b2c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2637838Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Egor Pasko <pasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844817}

tools/perf/cli_tools/pinpoint_traces.py

@@ -13,6 +13,7 @@ import multiprocessing
 import os
 import platform
 import re
+import shutil
 import subprocess
 import sys
 import traceback
@@ -239,7 +240,8 @@ def ExtractFromOneTraceThrowing(args):
     │       │   └── json.1
     │       ├── trace2
     │       │   ├── json
-    │       │   └── json.1
+    │       │   ├── json.1
+    │       │   └── json.2
     ├── chromium@5707819
     │   │
     │   ...
@@ -267,11 +269,17 @@ def ExtractFromOneTraceThrowing(args):
   (label, trace_index, html_trace, json_dir, compiled_regex) = args
   if not os.path.exists(json_dir):
     print 'Converting trace to json: {}'.format(json_dir)
-    EnsureDirectoryExists(json_dir)
-    temp_json = os.path.join(json_dir, '.tmp.json')
-    output = subprocess.check_output([HTML2TRACE, html_trace, temp_json])
-    for json_file in output.splitlines():
-      os.rename(json_file, os.path.join(json_dir, LastAfterSlash(json_file)))
+    tmp_json_dir = json_dir + '.tmp'
+    if os.path.exists(tmp_json_dir) and os.path.isdir(tmp_json_dir):
+      shutil.rmtree(tmp_json_dir)
+    EnsureDirectoryExists(tmp_json_dir)
+    json_file = os.path.join(tmp_json_dir, 'json')
+    output = subprocess.check_output([HTML2TRACE, html_trace, json_file])
+    for line in output.splitlines():
+      assert LastAfterSlash(line).startswith('json')
+    # Rename atomically to make sure that the JSON cache is not consumed
+    # partially.
+    os.rename(tmp_json_dir, json_dir)
 
   # Since several json files are produced from the same trace, an event could
   # begin and end in different jsons.
@@ -280,6 +288,7 @@ def ExtractFromOneTraceThrowing(args):
   print 'Taking trace: {}'.format(html_trace)
   for json_file in os.listdir(json_dir):
     if not json_file.startswith('json'):
+      print '{} not starting with json'.format(json_file)
       continue
     full_json_file = os.path.join(json_dir, json_file)
     tids = LoadJsonFile(full_json_file, compiled_regex)