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Diffstat (limited to 'bitbake/lib/bb/daemonize.py')
| -rw-r--r-- | bitbake/lib/bb/daemonize.py | 191 | 
1 files changed, 191 insertions, 0 deletions
| diff --git a/bitbake/lib/bb/daemonize.py b/bitbake/lib/bb/daemonize.py new file mode 100644 index 0000000000..1a8bb379f4 --- /dev/null +++ b/bitbake/lib/bb/daemonize.py @@ -0,0 +1,191 @@ +"""
 +Python Deamonizing helper
 +
 +Configurable daemon behaviors:
 +
 +   1.) The current working directory set to the "/" directory.
 +   2.) The current file creation mode mask set to 0.
 +   3.) Close all open files (1024). 
 +   4.) Redirect standard I/O streams to "/dev/null".
 +
 +A failed call to fork() now raises an exception.
 +
 +References:
 +   1) Advanced Programming in the Unix Environment: W. Richard Stevens
 +   2) Unix Programming Frequently Asked Questions:
 +         http://www.erlenstar.demon.co.uk/unix/faq_toc.html
 +
 +Modified to allow a function to be daemonized and return for 
 +bitbake use by Richard Purdie
 +"""
 +
 +__author__ = "Chad J. Schroeder"
 +__copyright__ = "Copyright (C) 2005 Chad J. Schroeder"
 +__version__ = "0.2"
 +
 +# Standard Python modules.
 +import os               # Miscellaneous OS interfaces.
 +import sys              # System-specific parameters and functions.
 +
 +# Default daemon parameters.
 +# File mode creation mask of the daemon.
 +# For BitBake's children, we do want to inherit the parent umask.
 +UMASK = None
 +
 +# Default maximum for the number of available file descriptors.
 +MAXFD = 1024
 +
 +# The standard I/O file descriptors are redirected to /dev/null by default.
 +if (hasattr(os, "devnull")):
 +   REDIRECT_TO = os.devnull
 +else:
 +   REDIRECT_TO = "/dev/null"
 +
 +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.
 +   """
 +
 +   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, 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()
 +
 +      # Is ignoring SIGHUP necessary?
 +      #
 +      # It's often suggested that the SIGHUP signal should be ignored before
 +      # the second fork to avoid premature termination of the process.  The
 +      # reason is that when the first child terminates, all processes, e.g.
 +      # the second child, in the orphaned group will be sent a SIGHUP.
 +      #
 +      # "However, as part of the session management system, there are exactly
 +      # two cases where SIGHUP is sent on the death of a process:
 +      #
 +      #   1) When the process that dies is the session leader of a session that
 +      #      is attached to a terminal device, SIGHUP is sent to all processes
 +      #      in the foreground process group of that terminal device.
 +      #   2) When the death of a process causes a process group to become
 +      #      orphaned, and one or more processes in the orphaned group are
 +      #      stopped, then SIGHUP and SIGCONT are sent to all members of the
 +      #      orphaned group." [2]
 +      #
 +      # The first case can be ignored since the child is guaranteed not to have
 +      # a controlling terminal.  The second case isn't so easy to dismiss.
 +      # The process group is orphaned when the first child terminates and
 +      # POSIX.1 requires that every STOPPED process in an orphaned process
 +      # group be sent a SIGHUP signal followed by a SIGCONT signal.  Since the
 +      # second child is not STOPPED though, we can safely forego ignoring the
 +      # SIGHUP signal.  In any case, there are no ill-effects if it is ignored.
 +      #
 +      # import signal           # Set handlers for asynchronous events.
 +      # signal.signal(signal.SIGHUP, signal.SIG_IGN)
 +
 +      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, e:
 +         raise Exception, "%s [%d]" % (e.strerror, e.errno)
 +
 +      if (pid == 0):	# The second child.
 +         # We probably don't want the file mode creation mask inherited from
 +         # the parent, so we give the child complete control over permissions.
 +         if UMASK is not None:
 +             os.umask(UMASK)
 +      else:
 +         # Parent (the first child) of the second child.
 +         os._exit(0)
 +   else:
 +      # 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.  Using exit() may cause all stdio
 +      # streams to be flushed twice and any temporary files may be unexpectedly
 +      # removed.  It's therefore recommended that child branches of a fork()
 +      # and the parent branch(es) of a daemon use _exit().
 +      return
 +
 +   # Close all open file descriptors.  This prevents the child from keeping
 +   # open any file descriptors inherited from the parent.  There is a variety
 +   # of methods to accomplish this task.  Three are listed below.
 +   #
 +   # Try the system configuration variable, SC_OPEN_MAX, to obtain the maximum
 +   # number of open file descriptors to close.  If it doesn't exists, use
 +   # the default value (configurable).
 +   #
 +   # try:
 +   #    maxfd = os.sysconf("SC_OPEN_MAX")
 +   # except (AttributeError, ValueError):
 +   #    maxfd = MAXFD
 +   #
 +   # OR
 +   #
 +   # if (os.sysconf_names.has_key("SC_OPEN_MAX")):
 +   #    maxfd = os.sysconf("SC_OPEN_MAX")
 +   # else:
 +   #    maxfd = MAXFD
 +   #
 +   # OR
 +   #
 +   # Use the getrlimit method to retrieve the maximum file descriptor number
 +   # that can be opened by this process.  If there is not limit on the
 +   # resource, use the default value.
 +   #
 +   import resource		# Resource usage information.
 +   maxfd = resource.getrlimit(resource.RLIMIT_NOFILE)[1]
 +   if (maxfd == resource.RLIM_INFINITY):
 +      maxfd = MAXFD
 +  
 +   # Iterate through and close all file descriptors.
 +#   for fd in range(0, maxfd):
 +#      try:
 +#         os.close(fd)
 +#      except OSError:	# ERROR, fd wasn't open to begin with (ignored)
 +#         pass
 +
 +   # Redirect the standard I/O file descriptors to the specified file.  Since
 +   # the daemon has no controlling terminal, most daemons redirect stdin,
 +   # stdout, and stderr to /dev/null.  This is done to prevent side-effects
 +   # from reads and writes to the standard I/O file descriptors.
 +
 +   # This call to open is guaranteed to return the lowest file descriptor,
 +   # which will be 0 (stdin), since it was closed above.
 +#   os.open(REDIRECT_TO, os.O_RDWR)	# standard input (0)
 +
 +   # Duplicate standard input to standard output and standard error.
 +#   os.dup2(0, 1)			# standard output (1)
 +#   os.dup2(0, 2)			# standard error (2)
 +
 +
 +   si = file('/dev/null', 'r')
 +   so = file(logfile, 'w')
 +   se = so
 +
 +
 +   # Replace those fds with our own
 +   os.dup2(si.fileno(), sys.stdin.fileno())
 +   os.dup2(so.fileno(), sys.stdout.fileno())
 +   os.dup2(se.fileno(), sys.stderr.fileno())
 +
 +   function()
 +
 +   os._exit(0)
 +
 | 
