review: Avoid race conditions if called multiple times

By always using unique filepaths (except for the final result, which is written atomically)
we turn multiple simultanious calls into at worst wasted effort, instead of garbled results.

restreamer/restreamer/review.py

@@ -4,6 +4,7 @@ import logging
 import os
 import subprocess
 from urlparse import urlparse
+from uuid import uuid4
 
 import mysql.connector
 
@@ -123,7 +124,8 @@ def review(match_id, race_number, base_dir, db_url, start_range=(0, 5), finish_r
 	finish_paths = []
 
 	for racer_number, racer in enumerate((racer1, racer2)):
-		start_path = os.path.join(output_dir, "start-{}.mp4".format(racer_number))
+		nonce = str(uuid4())
+		start_path = os.path.join(output_dir, "start-{}-{}.mp4".format(racer_number, nonce))
 
 		logger.info("Cutting start for racer {} ({})".format(racer_number, racer))
 		start_start, start_end = add_range(start, start_range)
@@ -159,12 +161,12 @@ def review(match_id, race_number, base_dir, db_url, start_range=(0, 5), finish_r
 		# time since their actual start.
 		finish_base = end + time_offset
 		finish_start, finish_end = add_range(finish_base, finish_range)
-		finish_path = os.path.join(output_dir, "finish-{}.mp4".format(racer_number))
+		finish_path = os.path.join(output_dir, "finish-{}-{}.mp4".format(racer_number, nonce))
 		finish_paths.append(finish_path)
 		logger.info("Got time offset of {}, cutting finish at finish_base {}".format(time_offset, finish_base))
 		cut_to_file(logger, finish_path, base_dir, racer, finish_start, finish_end)
 
-	temp_path = "{}.tmp.mp4".format(result_path)
+	temp_path = "{}.{}.mp4".format(result_path, str(uuid4()))
 	args = ['ffmpeg']
 	for path in finish_paths:
 		args += ['-i', path]