Reland: Optimize DeviceTempFile() by combining logic into a single "adb shell"

build/android/pylib/utils/device_temp_file.py

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """A temp file that automatically gets pushed and deleted from a device."""
 
 # pylint: disable=W0622
 
-import random
-import time
-
 from pylib import cmd_helper
 from pylib.device import device_errors
 
+_COMMAND_TEMPLATE = (
+    # Make sure that the temp dir is writable
+    'test -d {dir} && '
+    # If 5 random attempts fail, something is up.
+    'for i in 1 2 3 4 5; do '
+    'fn={dir}/{prefix}-$(date +%s)-"$RANDOM"{suffix};'
+    'test -e "$fn" || break;'
+    'done && '
+    # Touch the file, so other temp files can't get the same name.
+    'touch "$fn" && echo -n "$fn"')
 
 class DeviceTempFile(object):
   def __init__(self, adb, suffix='', prefix='temp_file', dir='/data/local/tmp'):
     """Find an unused temporary file path in the devices external directory.
 
     When this object is closed, the file will be deleted on the device.
 
     Args:
       adb: An instance of AdbWrapper
       suffix: The suffix of the name of the temp file.
       prefix: The prefix of the name of the temp file.
       dir: The directory on the device where to place the temp file.
     """
     self._adb = adb
-    # make sure that the temp dir is writable
-    self._adb.Shell('test -d %s' % cmd_helper.SingleQuote(dir))
-    while True:
-      self.name = '{dir}/{prefix}-{time:d}-{nonce:d}{suffix}'.format(
-        dir=dir, prefix=prefix, time=int(time.time()),
-        nonce=random.randint(0, 1000000), suffix=suffix)
-      self.name_quoted = cmd_helper.SingleQuote(self.name)
-      try:
-        self._adb.Shell('test -e %s' % self.name_quoted)
-      except device_errors.AdbCommandFailedError:
-        break # file does not exist
-
-    # Immediately touch the file, so other temp files can't get the same name.
-    self._adb.Shell('touch %s' % self.name_quoted)
+    command = _COMMAND_TEMPLATE.format(
+        dir=cmd_helper.SingleQuote(dir),
+        suffix=cmd_helper.SingleQuote(suffix),
+        prefix=cmd_helper.SingleQuote(prefix))
+    self.name = self._adb.Shell(command)
+    self.name_quoted = cmd_helper.SingleQuote(self.name)
 
   def close(self):
     """Deletes the temporary file from the device."""
     # ignore exception if the file is already gone.
     try:
       self._adb.Shell('rm -f %s' % self.name_quoted)
     except device_errors.AdbCommandFailedError:
       # file does not exist on Android version without 'rm -f' support (ICS)
       pass
 
   def __enter__(self):
     return self
 
   def __exit__(self, type, value, traceback):
     self.close()