os._exit() should be used rather than sys.exit() in the child process after a os.fork()

[Jun Omae]

According to the documentation of ​os._exit()t:

Exit the process with status n, without calling cleanup handlers, flushing stdio buffers, etc. Note: The standard way to exit is sys.exit(n). _exit() should normally only be used in the child process after a fork().

However, ​sys.exit() is used in daemonize()​.

trac/util/daemon.py

@@ -53 +53 @@
     # Perform first fork
     pid = os.fork()
     if pid > 0:
-        sys.exit(0) # exit first parent
+        os._exit(0)  # exit first parent
 
     # Decouple from parent environment
     os.chdir('/')
@@ -63 +63 @@
     # Perform second fork
     pid = os.fork()
     if pid > 0:
-        sys.exit(0) # exit second parent
+        os._exit(0)  # exit second parent
 
     # The process is now daemonized, redirect standard file descriptors
     for stream in sys.stdout, sys.stderr:

[Jun Omae]

Test script:

import sys
from trac.util.daemon import daemonize

sys.stdout.write('stdout')
sys.stderr.write('stderr')
daemonize()

Before the patch:

Data written to stdout and stderr before a call of daemonize are written to files thrice.

$ ~/venv/trac/1.6/bin/python /tmp/test-daemonize.py >/tmp/test-daemonize.stdout 2>/tmp/test-daemonize.stderr
$ ls -l /tmp/test-daemonize.std???
-rw-r--r-- 1 jun66j5 jun66j5 18 Jul  3 15:51 /tmp/test-daemonize.stderr
-rw-r--r-- 1 jun66j5 jun66j5 18 Jul  3 15:51 /tmp/test-daemonize.stdout
$ od -c /tmp/test-daemonize.stdout
0000000   s   t   d   o   u   t   s   t   d   o   u   t   s   t   d   o
0000020   u   t
0000022
$ od -c /tmp/test-daemonize.stderr
0000000   s   t   d   e   r   r   s   t   d   e   r   r   s   t   d   e
0000020   r   r
0000022

After the patch:

Data written to stdout and stderr before a call of daemonize are written to files only once.

$ PYTHONPATH=. ~/venv/py311/bin/python /tmp/test-daemonize.py >/tmp/test-daemonize.stdout 2>/tmp/test-daemonize.stderr
$ ls -l /tmp/test-daemonize.std???
-rw-r--r-- 1 jun66j5 jun66j5 6 Jul  3 15:58 /tmp/test-daemonize.stderr
-rw-r--r-- 1 jun66j5 jun66j5 6 Jul  3 15:58 /tmp/test-daemonize.stdout
$ od -c /tmp/test-daemonize.stdout
0000000   s   t   d   o   u   t
0000006
$ od -c /tmp/test-daemonize.stderr
0000000   s   t   d   e   r   r
0000006