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# Server process to keep track of unlinked resources (like shared memory
# segments, semaphores etc.) and clean them.
#
# On Unix we run a server process which keeps track of unlinked
# resources. The server ignores SIGINT and SIGTERM and reads from a
# pipe.  Every other process of the program has a copy of the writable
# end of the pipe, so we get EOF when all other processes have exited.
# Then the server process unlinks any remaining resource names.
#
# This is important because there may be system limits for such resources: for
# instance, the system only supports a limited number of named semaphores, and
# shared-memory segments live in the RAM. If a python process leaks such a
# resource, this resource will not be removed till the next reboot.  Without
# this resource tracker process, "killall python" would probably leave unlinked
# resources.

import os
import signal
import sys
import threading
import warnings

from . import spawn
from . import util

__all__ = ['ensure_running', 'register', 'unregister']

_HAVE_SIGMASK = hasattr(signal, 'pthread_sigmask')
_IGNORED_SIGNALS = (signal.SIGINT, signal.SIGTERM)

_CLEANUP_FUNCS = {
    'noop': lambda: None,
}

if os.name == 'posix':
    import _multiprocessing
    import _posixshmem

    _CLEANUP_FUNCS.update({
        'semaphore': _multiprocessing.sem_unlink,
        'shared_memory': _posixshmem.shm_unlink,
    })


class ResourceTracker(object):

    def __init__(self):
        self._lock = threading.Lock()
        self._fd = None
        self._pid = None

    def _stop(self):
        with self._lock:
            if self._fd is None:
                # not running
                return

            # closing the "alive" file descriptor stops main()
            os.close(self._fd)
            self._fd = None

            os.waitpid(self._pid, 0)
            self._pid = None

    def getfd(self):
        self.ensure_running()
        return self._fd

    def ensure_running(self):
        '''Make sure that resource tracker process is running.

        This can be run from any process.  Usually a child process will use
        the resource created by its parent.'''
        with self._lock:
            if self._fd is not None:
                # resource tracker was launched before, is it still running?
                if self._check_alive():
                    # => still alive
                    return
                # => dead, launch it again
                os.close(self._fd)

                # Clean-up to avoid dangling processes.
                try:
                    # _pid can be None if this process is a child from another
                    # python process, which has started the resource_tracker.
                    if self._pid is not None:
                        os.waitpid(self._pid, 0)
                except ChildProcessError:
                    # The resource_tracker has already been terminated.
                    pass
                self._fd = None
                self._pid = None

                warnings.warn('resource_tracker: process died unexpectedly, '
                              'relaunching.  Some resources might leak.')

            fds_to_pass = []
            try:
                fds_to_pass.append(sys.stderr.fileno())
            except Exception:
                pass
            cmd = 'from multiprocessing.resource_tracker import main;main(%d)'
            r, w = os.pipe()
            try:
                fds_to_pass.append(r)
                # process will out live us, so no need to wait on pid
                exe = spawn.get_executable()
                args = [exe] + util._args_from_interpreter_flags()
                args += ['-c', cmd % r]
                # bpo-33613: Register a signal mask that will block the signals.
                # This signal mask will be inherited by the child that is going
                # to be spawned and will protect the child from a race condition
                # tha