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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())
- try:
- so = open(logfile, 'a+')
- os.dup2(so.fileno(), sys.stdout.fileno())
- os.dup2(so.fileno(), sys.stderr.fileno())
- except io.UnsupportedOperation:
- sys.stdout = open(logfile, 'a+')
- # 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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