summaryrefslogtreecommitdiffstats
path: root/bitbake/lib/bb/daemonize.py
blob: 346a6185820ab5e3365e85d649795a99c4283c17 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
"""
Python Daemonizing 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
	http://www.apuebook.com/apue3e.html
    2) The Linux Programming Interface: Michael Kerrisk
	http://man7.org/tlpi/index.html
    3) Unix Programming Frequently Asked Questions:
	http://www.faqs.org/faqs/unix-faq/programmer/faq/

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 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()

        # 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 as 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 exist, 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 no 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)