First version. Most definitely a work in progress.

[nodemanager.git] / tools.py

diff --git a/tools.py b/tools.py
new file mode 100644 (file)
index 0000000..bc391a9
--- /dev/null
+++ b/tools.py
@@ -0,0 +1,89 @@
+import cPickle
+import errno
+import os
+import pwd
+import tempfile
+import threading
+
+from config import PID_FILE
+import logger
+
+
+def as_daemon_thread(run):
+    thr = threading.Thread(target=run)
+    thr.setDaemon(True)
+    thr.start()
+
+
+# after http://www.erlenstar.demon.co.uk/unix/faq_2.html
+def daemon():
+    """Daemonize the current process."""
+    if os.fork() != 0: os._exit(0)
+    os.setsid()
+    if os.fork() != 0: os._exit(0)
+    os.chdir('/')
+    os.umask(0)
+    devnull = os.open(os.devnull, os.O_RDWR)
+    for fd in range(3): os.dup2(devnull, fd)
+
+
+def deepcopy(obj):
+    """Return a deep copy of obj."""
+    return cPickle.loads(cPickle.dumps(obj, -1))
+
+
+def fork_as(su, function, *args):
+    """fork(), cd / to avoid keeping unused directories open, close all nonstandard file descriptors (to avoid capturing open sockets), fork() again (to avoid zombies) and call <function> with arguments <args> in the grandchild process.  If <su> is not None, set our group and user ids appropriately in the child process."""
+    child_pid = os.fork()
+    if child_pid == 0:
+        try:
+            os.chdir('/')
+            # close all nonstandard file descriptors
+            _SC_OPEN_MAX = 4
+            for fd in range(3, os.sysconf(_SC_OPEN_MAX)):
+                try: os.close(fd)
+                except OSError: pass  # most likely an fd that isn't open
+            pw_ent = pwd.getpwnam(su)
+            os.setegid(pw_ent[3])
+            os.seteuid(pw_ent[2])
+            child_pid = os.fork()
+            if child_pid == 0: function(*args)
+        except:
+            os.seteuid(os.getuid())  # undo su so we can write the log file
+            os.setegid(os.getgid())
+            logger.log_exc()
+        os._exit(0)
+    else: os.waitpid(child_pid, 0)
+
+
+def pid_file():
+    """We use a pid file to ensure that only one copy of NM is running at a given time.  If successful, this function will write a pid file containing the pid of the current process.  The return value is the pid of the other running process, or None otherwise."""
+    other_pid = None
+    # check for a pid file
+    if os.access(PID_FILE, os.F_OK):
+        # pid file exists, read it
+        handle = open(PID_FILE)
+        other_pid = int(handle.read())
+        handle.close()
+        # check for a process with that pid by sending signal 0
+        try: os.kill(other_pid, 0)
+        except OSError, e:
+            if e.errno == errno.ESRCH: other_pid = None  # doesn't exist
+            else: raise  # who knows
+    if other_pid == None:
+        # write a new pid file
+        write_file(PID_FILE, lambda thefile: thefile.write(str(os.getpid())))
+    return other_pid
+
+
+def write_file(filename, do_write):
+    """Write file <filename> atomically by opening a temporary file, using <do_write> to write that file, and then renaming the temporary file."""
+    os.rename(write_temp_file(do_write), filename)
+
+
+def write_temp_file(do_write):
+    fd, temporary_filename = tempfile.mkstemp()
+    thefile = os.fdopen(fd, 'w')
+    do_write(thefile)
+    thefile.close()
+    return temporary_filename