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Diffstat (limited to 'bitbake/lib/bb/daemonize.py')
| -rw-r--r-- | bitbake/lib/bb/daemonize.py | 190 |
1 files changed, 190 insertions, 0 deletions
diff --git a/bitbake/lib/bb/daemonize.py b/bitbake/lib/bb/daemonize.py new file mode 100644 index 0000000000..f0714b3af6 --- /dev/null +++ b/bitbake/lib/bb/daemonize.py | |||
| @@ -0,0 +1,190 @@ | |||
| 1 | """ | ||
| 2 | Python Deamonizing helper | ||
| 3 | |||
| 4 | Configurable daemon behaviors: | ||
| 5 | |||
| 6 | 1.) The current working directory set to the "/" directory. | ||
| 7 | 2.) The current file creation mode mask set to 0. | ||
| 8 | 3.) Close all open files (1024). | ||
| 9 | 4.) Redirect standard I/O streams to "/dev/null". | ||
| 10 | |||
| 11 | A failed call to fork() now raises an exception. | ||
| 12 | |||
| 13 | References: | ||
| 14 | 1) Advanced Programming in the Unix Environment: W. Richard Stevens | ||
| 15 | 2) Unix Programming Frequently Asked Questions: | ||
| 16 | http://www.erlenstar.demon.co.uk/unix/faq_toc.html | ||
| 17 | |||
| 18 | Modified to allow a function to be daemonized and return for | ||
| 19 | bitbake use by Richard Purdie | ||
| 20 | """ | ||
| 21 | |||
| 22 | __author__ = "Chad J. Schroeder" | ||
| 23 | __copyright__ = "Copyright (C) 2005 Chad J. Schroeder" | ||
| 24 | __version__ = "0.2" | ||
| 25 | |||
| 26 | # Standard Python modules. | ||
| 27 | import os # Miscellaneous OS interfaces. | ||
| 28 | import sys # System-specific parameters and functions. | ||
| 29 | |||
| 30 | # Default daemon parameters. | ||
| 31 | # File mode creation mask of the daemon. | ||
| 32 | # For BitBake's children, we do want to inherit the parent umask. | ||
| 33 | UMASK = None | ||
| 34 | |||
| 35 | # Default maximum for the number of available file descriptors. | ||
| 36 | MAXFD = 1024 | ||
| 37 | |||
| 38 | # The standard I/O file descriptors are redirected to /dev/null by default. | ||
| 39 | if (hasattr(os, "devnull")): | ||
| 40 | REDIRECT_TO = os.devnull | ||
| 41 | else: | ||
| 42 | REDIRECT_TO = "/dev/null" | ||
| 43 | |||
| 44 | def createDaemon(function, logfile): | ||
| 45 | """ | ||
| 46 | Detach a process from the controlling terminal and run it in the | ||
| 47 | background as a daemon, returning control to the caller. | ||
| 48 | """ | ||
| 49 | |||
| 50 | try: | ||
| 51 | # Fork a child process so the parent can exit. This returns control to | ||
| 52 | # the command-line or shell. It also guarantees that the child will not | ||
| 53 | # be a process group leader, since the child receives a new process ID | ||
| 54 | # and inherits the parent's process group ID. This step is required | ||
| 55 | # to insure that the next call to os.setsid is successful. | ||
| 56 | pid = os.fork() | ||
| 57 | except OSError as e: | ||
| 58 | raise Exception("%s [%d]" % (e.strerror, e.errno)) | ||
| 59 | |||
| 60 | if (pid == 0): # The first child. | ||
| 61 | # To become the session leader of this new session and the process group | ||
| 62 | # leader of the new process group, we call os.setsid(). The process is | ||
| 63 | # also guaranteed not to have a controlling terminal. | ||
| 64 | os.setsid() | ||
| 65 | |||
| 66 | # Is ignoring SIGHUP necessary? | ||
| 67 | # | ||
| 68 | # It's often suggested that the SIGHUP signal should be ignored before | ||
| 69 | # the second fork to avoid premature termination of the process. The | ||
| 70 | # reason is that when the first child terminates, all processes, e.g. | ||
| 71 | # the second child, in the orphaned group will be sent a SIGHUP. | ||
| 72 | # | ||
| 73 | # "However, as part of the session management system, there are exactly | ||
| 74 | # two cases where SIGHUP is sent on the death of a process: | ||
| 75 | # | ||
| 76 | # 1) When the process that dies is the session leader of a session that | ||
| 77 | # is attached to a terminal device, SIGHUP is sent to all processes | ||
| 78 | # in the foreground process group of that terminal device. | ||
| 79 | # 2) When the death of a process causes a process group to become | ||
| 80 | # orphaned, and one or more processes in the orphaned group are | ||
| 81 | # stopped, then SIGHUP and SIGCONT are sent to all members of the | ||
| 82 | # orphaned group." [2] | ||
| 83 | # | ||
| 84 | # The first case can be ignored since the child is guaranteed not to have | ||
| 85 | # a controlling terminal. The second case isn't so easy to dismiss. | ||
| 86 | # The process group is orphaned when the first child terminates and | ||
| 87 | # POSIX.1 requires that every STOPPED process in an orphaned process | ||
| 88 | # group be sent a SIGHUP signal followed by a SIGCONT signal. Since the | ||
| 89 | # second child is not STOPPED though, we can safely forego ignoring the | ||
| 90 | # SIGHUP signal. In any case, there are no ill-effects if it is ignored. | ||
| 91 | # | ||
| 92 | # import signal # Set handlers for asynchronous events. | ||
| 93 | # signal.signal(signal.SIGHUP, signal.SIG_IGN) | ||
| 94 | |||
| 95 | try: | ||
| 96 | # Fork a second child and exit immediately to prevent zombies. This | ||
| 97 | # causes the second child process to be orphaned, making the init | ||
| 98 | # process responsible for its cleanup. And, since the first child is | ||
| 99 | # a session leader without a controlling terminal, it's possible for | ||
| 100 | # it to acquire one by opening a terminal in the future (System V- | ||
| 101 | # based systems). This second fork guarantees that the child is no | ||
| 102 | # longer a session leader, preventing the daemon from ever acquiring | ||
| 103 | # a controlling terminal. | ||
| 104 | pid = os.fork() # Fork a second child. | ||
| 105 | except OSError as e: | ||
| 106 | raise Exception("%s [%d]" % (e.strerror, e.errno)) | ||
| 107 | |||
| 108 | if (pid == 0): # The second child. | ||
| 109 | # We probably don't want the file mode creation mask inherited from | ||
| 110 | # the parent, so we give the child complete control over permissions. | ||
| 111 | if UMASK is not None: | ||
| 112 | os.umask(UMASK) | ||
| 113 | else: | ||
| 114 | # Parent (the first child) of the second child. | ||
| 115 | os._exit(0) | ||
| 116 | else: | ||
| 117 | # exit() or _exit()? | ||
| 118 | # _exit is like exit(), but it doesn't call any functions registered | ||
| 119 | # with atexit (and on_exit) or any registered signal handlers. It also | ||
| 120 | # closes any open file descriptors. Using exit() may cause all stdio | ||
| 121 | # streams to be flushed twice and any temporary files may be unexpectedly | ||
| 122 | # removed. It's therefore recommended that child branches of a fork() | ||
| 123 | # and the parent branch(es) of a daemon use _exit(). | ||
| 124 | return | ||
| 125 | |||
| 126 | # Close all open file descriptors. This prevents the child from keeping | ||
| 127 | # open any file descriptors inherited from the parent. There is a variety | ||
| 128 | # of methods to accomplish this task. Three are listed below. | ||
| 129 | # | ||
| 130 | # Try the system configuration variable, SC_OPEN_MAX, to obtain the maximum | ||
| 131 | # number of open file descriptors to close. If it doesn't exists, use | ||
| 132 | # the default value (configurable). | ||
| 133 | # | ||
| 134 | # try: | ||
| 135 | # maxfd = os.sysconf("SC_OPEN_MAX") | ||
| 136 | # except (AttributeError, ValueError): | ||
| 137 | # maxfd = MAXFD | ||
| 138 | # | ||
| 139 | # OR | ||
| 140 | # | ||
| 141 | # if (os.sysconf_names.has_key("SC_OPEN_MAX")): | ||
| 142 | # maxfd = os.sysconf("SC_OPEN_MAX") | ||
| 143 | # else: | ||
| 144 | # maxfd = MAXFD | ||
| 145 | # | ||
| 146 | # OR | ||
| 147 | # | ||
| 148 | # Use the getrlimit method to retrieve the maximum file descriptor number | ||
| 149 | # that can be opened by this process. If there is not limit on the | ||
| 150 | # resource, use the default value. | ||
| 151 | # | ||
| 152 | import resource # Resource usage information. | ||
| 153 | maxfd = resource.getrlimit(resource.RLIMIT_NOFILE)[1] | ||
| 154 | if (maxfd == resource.RLIM_INFINITY): | ||
| 155 | maxfd = MAXFD | ||
| 156 | |||
| 157 | # Iterate through and close all file descriptors. | ||
| 158 | # for fd in range(0, maxfd): | ||
| 159 | # try: | ||
| 160 | # os.close(fd) | ||
| 161 | # except OSError: # ERROR, fd wasn't open to begin with (ignored) | ||
| 162 | # pass | ||
| 163 | |||
| 164 | # Redirect the standard I/O file descriptors to the specified file. Since | ||
| 165 | # the daemon has no controlling terminal, most daemons redirect stdin, | ||
| 166 | # stdout, and stderr to /dev/null. This is done to prevent side-effects | ||
| 167 | # from reads and writes to the standard I/O file descriptors. | ||
| 168 | |||
| 169 | # This call to open is guaranteed to return the lowest file descriptor, | ||
| 170 | # which will be 0 (stdin), since it was closed above. | ||
| 171 | # os.open(REDIRECT_TO, os.O_RDWR) # standard input (0) | ||
| 172 | |||
| 173 | # Duplicate standard input to standard output and standard error. | ||
| 174 | # os.dup2(0, 1) # standard output (1) | ||
| 175 | # os.dup2(0, 2) # standard error (2) | ||
| 176 | |||
| 177 | |||
| 178 | si = file('/dev/null', 'r') | ||
| 179 | so = file(logfile, 'w') | ||
| 180 | se = so | ||
| 181 | |||
| 182 | |||
| 183 | # Replace those fds with our own | ||
| 184 | os.dup2(si.fileno(), sys.stdin.fileno()) | ||
| 185 | os.dup2(so.fileno(), sys.stdout.fileno()) | ||
| 186 | os.dup2(se.fileno(), sys.stderr.fileno()) | ||
| 187 | |||
| 188 | function() | ||
| 189 | |||
| 190 | os._exit(0) | ||
