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#
# SPDX-License-Identifier: GPL-2.0-only
#
"""
Python Daemonizing helper
Originally based on code Copyright (C) 2005 Chad J. Schroeder but now heavily modified
to allow a function to be daemonized and return for bitbake use by Richard Purdie
"""
import os
import sys
import io
import traceback
import bb
def createDaemon(function, logfile):
"""
Detach a process from the controlling terminal and run it in the
background as a daemon, returning control to the caller.
"""
# Ensure stdout/stderror are flushed before forking to avoid duplicate output
sys.stdout.flush()
sys.stderr.flush()
try:
# Fork a child process so the parent can exit. This returns control to
# the command-line or shell. It also guarantees that the child will not
# be a process group leader, since the child receives a new process ID
# and inherits the parent's process group ID. This step is required
# to insure that the next call to os.setsid is successful.
pid = os.fork()
except OSError as e:
raise Exception("%s [%d]" % (e.strerror, e.errno))
if (pid == 0): # The first child.
# To become the session leader of this new session and the process group
# leader of the new process group, we call os.setsid(). The process is
# also guaranteed not to have a controlling terminal.
os.setsid()
try:
# Fork a second child and exit immediately to prevent zombies. This
# causes the second child process to be orphaned, making the init
# process responsible for its cleanup. And, since the first child is
# a session leader without a controlling terminal, it's possible for
# it to acquire one by opening a terminal in the future (System V-
# based systems). This second fork guarantees that the child is no
# longer a session leader, preventing the daemon from ever acquiring
# a controlling terminal.
pid = os.fork() # Fork a second child.
except OSError as e:
raise Exception("%s [%d]" % (e.strerror, e.errno))
if (pid != 0):
# Parent (the first child) of the second child.
# exit() or _exit()?
# _exit is like exit(), but it doesn't call any functions registered
# with atexit (and on_exit) or any registered signal handlers. It also
# closes any open file descriptors, but doesn't flush any buffered output.
# Using exit() may cause all any temporary files to be unexpectedly
# removed. It's therefore recommended that child branches of a fork()
# and the parent branch(es) of a daemon use _exit().
os._exit(0)
else:
os.waitpid(pid, 0)
return
# The second child.
# Replace standard fds with our own
with open('/dev/null', 'r') as si:
os.dup2(si.fileno(), sys.stdin.fileno())
with open(logfile, 'a+') as so:
try:
os.dup2(so.fileno(), sys.stdout.fileno())
os.dup2(so.fileno(), sys.stderr.fileno())
except io.UnsupportedOperation:
sys.stdout = so
# Have stdout and stderr be the same so log output matches chronologically
# and there aren't two seperate buffers
sys.stderr = sys.stdout
try:
function()
except Exception as e:
traceback.print_exc()
finally:
bb.event.print_ui_queue()
# os._exit() doesn't flush open files like os.exit() does. Manually flush
# stdout and stderr so that any logging output will be seen, particularly
# exception tracebacks.
sys.stdout.flush()
sys.stderr.flush()
os._exit(0)
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