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