Mini Shell

#
# Module implementing synchronization primitives
#
# multiprocessing/synchronize.py
#
# Copyright (c) 2006-2008, R Oudkerk
# Licensed to PSF under a Contributor Agreement.
#

import errno
import sys
import tempfile
import threading

from . import context
from . import process
from . import util

from ._ext import _billiard, ensure_SemLock
from time import monotonic

__all__ = [
    'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore', 'Condition', 'Event',
]

# Try to import the mp.synchronize module cleanly, if it fails
# raise ImportError for platforms lacking a working sem_open implementation.
# See issue 3770
ensure_SemLock()

#
# Constants
#

RECURSIVE_MUTEX, SEMAPHORE = list(range(2))
SEM_VALUE_MAX = _billiard.SemLock.SEM_VALUE_MAX

try:
    sem_unlink = _billiard.SemLock.sem_unlink
except AttributeError:  # pragma: no cover
    try:
        # Py3.4+ implements sem_unlink and the semaphore must be named
        from _multiprocessing import sem_unlink  # noqa
    except ImportError:
        sem_unlink = None   # noqa

#
# Base class for semaphores and mutexes; wraps `_billiard.SemLock`
#


def _semname(sl):
    try:
        return sl.name
    except AttributeError:
        pass


class SemLock:
    _rand = tempfile._RandomNameSequence()

    def __init__(self, kind, value, maxvalue, ctx=None):
        if ctx is None:
            ctx = context._default_context.get_context()
        name = ctx.get_start_method()
        unlink_now = sys.platform == 'win32' or name == 'fork'
        if sem_unlink:
            for i in range(100):
                try:
                    sl = self._semlock = _billiard.SemLock(
                        kind, value, maxvalue, self._make_name(), unlink_now,
                    )
                except (OSError, IOError) as exc:
                    if getattr(exc, 'errno', None) != errno.EEXIST:
                        raise
                else:
                    break
            else:
                exc = IOError('cannot find file for semaphore')
                exc.errno = errno.EEXIST
                raise exc
        else:
            sl = self._semlock = _billiard.SemLock(kind, value, maxvalue)

        util.debug('created semlock with handle %s', sl.handle)
        self._make_methods()

        if sem_unlink:

            if sys.platform != 'win32':
                def _after_fork(obj):
                    obj._semlock._after_fork()
                util.register_after_fork(self, _after_fork)

            if _semname(self._semlock) is not None:
                # We only get here if we are on Unix with forking
                # disabled.  When the object is garbage collected or the
                # process shuts down we unlink the semaphore name
                from .semaphore_tracker import register
                register(self._semlock.name)
                util.Finalize(self, SemLock._cleanup, (self._semlock.name,),
                              exitpriority=0)

    @staticmethod
    def _cleanup(name):
        from .semaphore_tracker import unregister
        sem_unlink(name)
        unregister(name)

    def _make_methods(self):
        self.acquire = self._semlock.acquire
        self.release = self._semlock.release

    def __enter__(self):
        return self._semlock.__enter__()

    def __exit__(self, *args):
        return self._semlock.__exit__(*args)

    def __getstate__(self):
        context.assert_spawning(self)
        sl = self._semlock
        if sys.platform == 'win32':
            h = context.get_spawning_popen().duplicate_for_child(sl.handle)
        else:
            h = sl.handle
        state = (h, sl.kind, sl.maxvalue)
        try:
            state += (sl.name, )
        except AttributeError:
            pass
        return state

    def __setstate__(self, state):
        self._semlock = _billiard.SemLock._rebuild(*state)
        util.debug('recreated blocker with handle %r', state[0])
        self._make_methods()

    @staticmethod
    def _make_name():
        return '%s-%s' % (process.current_process()._config['semprefix'],
                          next(SemLock._rand))


class Semaphore(SemLock):

    def __init__(self, value=1, ctx=None):
        SemLock.__init__(self, SEMAPHORE, value, SEM_VALUE_MAX, ctx=ctx)

    def get_value(self):
        return self._semlock._get_value()

    def __repr__(self):
        try:
            value = self._semlock._get_value()
        except Exception:
            value = 'unknown'
        return '<%s(value=%s)>' % (self.__class__.__name__, value)


class BoundedSemaphore(Semaphore):

    def __init__(self, value=1, ctx=None):
        SemLock.__init__(self, SEMAPHORE, value, value, ctx=ctx)

    def __repr__(self):
        try:
            value = self._semlock._get_value()
        except Exception:
            value = 'unknown'
        return '<%s(value=%s, maxvalue=%s)>' % (
            self.__class__.__name__, value, self._semlock.maxvalue)


class Lock(SemLock):
    '''
    Non-recursive lock.
    '''

    def __init__(self, ctx=None):
        SemLock.__init__(self, SEMAPHORE, 1, 1, ctx=ctx)

    def __repr__(self):
        try:
            if self._semlock._is_mine():
                name = process.current_process().name
                if threading.current_thread().name != 'MainThread':
                    name += '|' + threading.current_thread().name
            elif self._semlock._get_value() == 1:
                name = 'None'
            elif self._semlock._count() > 0:
                name = 'SomeOtherThread'
            else:
                name = 'SomeOtherProcess'
        except Exception:
            name = 'unknown'
        return '<%s(owner=%s)>' % (self.__class__.__name__, name)


class RLock(SemLock):
    '''
    Recursive lock
    '''

    def __init__(self, ctx=None):
        SemLock.__init__(self, RECURSIVE_MUTEX, 1, 1, ctx=ctx)

    def __repr__(self):
        try:
            if self._semlock._is_mine():
                name = process.current_process().name
                if threading.current_thread().name != 'MainThread':
                    name += '|' + threading.current_thread().name
                count = self._semlock._count()
            elif self._semlock._get_value() == 1:
                name, count = 'None', 0
            elif self._semlock._count() > 0:
                name, count = 'SomeOtherThread', 'nonzero'
            else:
                name, count = 'SomeOtherProcess', 'nonzero'
        except Exception:
            name, count = 'unknown', 'unknown'
        return '<%s(%s, %s)>' % (self.__class__.__name__, name, count)


class Condition:
    '''
    Condition variable
    '''

    def __init__(self, lock=None, ctx=None):
        assert ctx
        self._lock = lock or ctx.RLock()
        self._sleeping_count = ctx.Semaphore(0)
        self._woken_count = ctx.Semaphore(0)
        self._wait_semaphore = ctx.Semaphore(0)
        self._make_methods()

    def __getstate__(self):
        context.assert_spawning(self)
        return (self._lock, self._sleeping_count,
                self._woken_count, self._wait_semaphore)

    def __setstate__(self, state):
        (self._lock, self._sleeping_count,
         self._woken_count, self._wait_semaphore) = state
        self._make_methods()

    def __enter__(self):
        return self._lock.__enter__()

    def __exit__(self, *args):
        return self._lock.__exit__(*args)

    def _make_methods(self):
        self.acquire = self._lock.acquire
        self.release = self._lock.release

    def __repr__(self):
        try:
            num_waiters = (self._sleeping_count._semlock._get_value() -
                           self._woken_count._semlock._get_value())
        except Exception:
            num_waiters = 'unknown'
        return '<%s(%s, %s)>' % (
            self.__class__.__name__, self._lock, num_waiters)

    def wait(self, timeout=None):
        assert self._lock._semlock._is_mine(), \
            'must acquire() condition before using wait()'

        # indicate that this thread is going to sleep
        self._sleeping_count.release()

        # release lock
        count = self._lock._semlock._count()
        for i in range(count):
            self._lock.release()

        try:
            # wait for notification or timeout
            return self._wait_semaphore.acquire(True, timeout)
        finally:
            # indicate that this thread has woken
            self._woken_count.release()

            # reacquire lock
            for i in range(count):
                self._lock.acquire()

    def notify(self):
        assert self._lock._semlock._is_mine(), 'lock is not owned'
        assert not self._wait_semaphore.acquire(False)

        # to take account of timeouts since last notify() we subtract
        # woken_count from sleeping_count and rezero woken_count
        while self._woken_count.acquire(False):
            res = self._sleeping_count.acquire(False)
            assert res

        if self._sleeping_count.acquire(False):  # try grabbing a sleeper
            self._wait_semaphore.release()       # wake up one sleeper
            self._woken_count.acquire()          # wait for sleeper to wake

            # rezero _wait_semaphore in case a timeout just happened
            self._wait_semaphore.acquire(False)

    def notify_all(self):
        assert self._lock._semlock._is_mine(), 'lock is not owned'
        assert not self._wait_semaphore.acquire(False)

        # to take account of timeouts since last notify*() we subtract
        # woken_count from sleeping_count and rezero woken_count
        while self._woken_count.acquire(False):
            res = self._sleeping_count.acquire(False)
            assert res

        sleepers = 0
        while self._sleeping_count.acquire(False):
            self._wait_semaphore.release()        # wake up one sleeper
            sleepers += 1

        if sleepers:
            for i in range(sleepers):
                self._woken_count.acquire()       # wait for a sleeper to wake

            # rezero wait_semaphore in case some timeouts just happened
            while self._wait_semaphore.acquire(False):
                pass

    def wait_for(self, predicate, timeout=None):
        result = predicate()
        if result:
            return result
        if timeout is not None:
            endtime = monotonic() + timeout
        else:
            endtime = None
            waittime = None
        while not result:
            if endtime is not None:
                waittime = endtime - monotonic()
                if waittime <= 0:
                    break
            self.wait(waittime)
            result = predicate()
        return result


class Event:

    def __init__(self, ctx=None):
        assert ctx
        self._cond = ctx.Condition(ctx.Lock())
        self._flag = ctx.Semaphore(0)

    def is_set(self):
        with self._cond:
            if self._flag.acquire(False):
                self._flag.release()
                return True
            return False

    def set(self):
        with self._cond:
            self._flag.acquire(False)
            self._flag.release()
            self._cond.notify_all()

    def clear(self):
        with self._cond:
            self._flag.acquire(False)

    def wait(self, timeout=None):
        with self._cond:
            if self._flag.acquire(False):
                self._flag.release()
            else:
                self._cond.wait(timeout)

            if self._flag.acquire(False):
                self._flag.release()
                return True
            return False

#
# Barrier
#


if hasattr(threading, 'Barrier'):

    class Barrier(threading.Barrier):

        def __init__(self, parties, action=None, timeout=None, ctx=None):
            assert ctx
            import struct
            from .heap import BufferWrapper
            wrapper = BufferWrapper(struct.calcsize('i') * 2)
            cond = ctx.Condition()
            self.__setstate__((parties, action, timeout, cond, wrapper))
            self._state = 0
            self._count = 0

        def __setstate__(self, state):
            (self._parties, self._action, self._timeout,
             self._cond, self._wrapper) = state
            self._array = self._wrapper.create_memoryview().cast('i')

        def __getstate__(self):
            return (self._parties, self._action, self._timeout,
                    self._cond, self._wrapper)

        @property
        def _state(self):
            return self._array[0]

        @_state.setter
        def _state(self, value):  # noqa
            self._array[0] = value

        @property
        def _count(self):
            return self._array[1]

        @_count.setter
        def _count(self, value):  # noqa
            self._array[1] = value


else:

    class Barrier:  # noqa

        def __init__(self, *args, **kwargs):
            raise NotImplementedError('Barrier only supported on Py3')