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

build/android/adb_logcat_monitor.py

Index: build/android/adb_logcat_monitor.py
diff --git a/build/android/adb_logcat_monitor.py b/build/android/adb_logcat_monitor.py
index 35ef7905b24fcb9a30506f5e0d246d3f52085214..0f26c9ace4a7b2da980e1d71281cc5553020e438 100755
--- a/build/android/adb_logcat_monitor.py
+++ b/build/android/adb_logcat_monitor.py
@@ -96,6 +96,15 @@ def GetAttachedDevices(adb_cmd):
 
 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:
+    return 0

[Isaac (away), 2013/09/26 18:31:08]

yikes.  I believe this needs to be os._exit(0)

[Siva Chandra, 2013/09/26 20:24:13]

I think in principle this should be the other way: child process should exit
os._exit(...). However, in this case, we are always doing this right at the
beginning and always guaranteed that the parent process dies before the child
without creating any shared resources. Hence, exit from parent and child seem
safe enough. This is based on my understanding. You can explain more and help me
understand better if I got it wrong.

+  elif pid < 0:
+    sys.exit('Unable to spawn a detached child process.')
+  os.setsid()

[iannucci, 2013/09/26 18:15:57]

How does this process get cleaned up?

[Siva Chandra, 2013/09/26 18:30:06]

There is another step which is always executed. That step cleans this up.

[Isaac (away), 2013/09/26 18:31:08]

Another process reads PID from a file and kills it.  An alternative here would
be to revamp the way the logger works -- which might less error prone than using
a raw fork (which again, is really dangerous).

[navabi, 2013/09/26 19:56:00]

Where does that happen again? I don't see the PID being written to a file.
Can you point me to the step that is executed and cleans this up? Is it in a
finally block?

[Siva Chandra, 2013/09/26 20:29:44]

See below.

+  # 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