[Android] Fork a detached child process from adb_logcat_monitor.py.

build/android/adb_logcat_monitor.py

 #!/usr/bin/env python
 #
 # Copyright (c) 2012 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.
 
 """Saves logcats from all connected devices.
 
 Usage: adb_logcat_monitor.py <base_dir> [<adb_binary_path>]
 
@@ skipping 78 matching lines @@
     return []
   except (IOError, OSError):
     logging.exception('Exception from "adb devices"')
     return []
   finally:
     signal.alarm(0)
 
 
 def main(base_dir, adb_cmd='adb'):
   """Monitor adb forever.  Expects a SIGINT (Ctrl-C) to kill."""
+  # Spawn a detached child process.
+  pid = os.fork()
+  if pid > 0:
+    os._exit(os.EX_OK)
+  elif pid < 0:
+    sys.exit('Unable to spawn a detached child process.')
+  os.setsid()
+  # The rest happens in the child process.
+
   # We create the directory to ensure 'run once' semantics
   if os.path.exists(base_dir):
     print 'adb_logcat_monitor: %s already exists? Cleaning' % base_dir
     shutil.rmtree(base_dir, ignore_errors=True)
 
   os.makedirs(base_dir)
   logging.basicConfig(filename=os.path.join(base_dir, 'eventlog'),
                       level=logging.INFO,
                       format='%(asctime)-2s %(levelname)-8s %(message)s')
 
@@ skipping 38 matching lines @@
           pass
     os.remove(pid_file_path)
 
 
 if __name__ == '__main__':
   if 2 <= len(sys.argv) <= 3:
     print 'adb_logcat_monitor: Initializing'
     sys.exit(main(*sys.argv[1:3]))
 
   print 'Usage: %s <base_dir> [<adb_binary_path>]' % sys.argv[0]