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#

#

# Copyright (C) 2006, 2007 Google Inc.

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful, but

# WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

# General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

# 02110-1301, USA.

"""Module implementing the Ganeti locking code."""

import os

import select

import threading

import time

import errno

from ganeti import errors

from ganeti import utils

def ssynchronized(lock, shared=0):

  """Shared Synchronization decorator.

  Calls the function holding the given lock, either in exclusive or shared

  mode. It requires the passed lock to be a SharedLock (or support its

  semantics).

  """

  def wrap(fn):

    def sync_function(*args, **kwargs):

      lock.acquire(shared=shared)

      try:

        return fn(*args, **kwargs)

      finally:

        lock.release()

    return sync_function

  return wrap

class _SingleActionPipeConditionWaiter(object):

  """Callable helper class for _SingleActionPipeCondition.

  """

  __slots__ = [

    "_cond",

    "_fd",

    "_poller",

    ]

  def __init__(self, cond, poller, fd):

    """Initializes this class.

    @type cond: L{_SingleActionPipeCondition}

    @param cond: Parent condition

    @type poller: select.poll

    @param poller: Poller object

    @type fd: int

    @param fd: File descriptor to wait for

    """

    object.__init__(self)

    self._cond = cond

    self._poller = poller

    self._fd = fd

  def __call__(self, timeout):

    """Wait for something to happen on the pipe.

    @type timeout: float or None

    @param timeout: Timeout for waiting (can be None)

    """

    start_time = time.time()

    remaining_time = timeout

    while timeout is None or remaining_time > 0:

      try:

        result = self._poller.poll(remaining_time)

      except EnvironmentError, err:

        if err.errno != errno.EINTR:

          raise

        result = None

      # Check whether we were notified

      if result and result[0][0] == self._fd:

        break

      # Re-calculate timeout if necessary

      if timeout is not None:

        remaining_time = start_time + timeout - time.time()

class _BaseCondition(object):

  """Base class containing common code for conditions.

  Some of this code is taken from python's threading module.

  """

  __slots__ = [

    "_lock",

    "acquire",

    "release",

    ]

  def __init__(self, lock):

    """Constructor for _BaseCondition.

    @type lock: L{threading.Lock}

    @param lock: condition base lock

    """

    object.__init__(self)

    # Recursive locks are not supported

    assert not hasattr(lock, "_acquire_restore")

    assert not hasattr(lock, "_release_save")

    self._lock = lock

    # Export the lock's acquire() and release() methods

    self.acquire = lock.acquire

    self.release = lock.release

  def _is_owned(self):

    """Check whether lock is owned by current thread.

    """

    if self._lock.acquire(0):

      self._lock.release()

      return False

    return True

  def _check_owned(self):

    """Raise an exception if the current thread doesn't own the lock.

    """

    if not self._is_owned():

      raise RuntimeError("cannot work with un-aquired lock")

class _SingleActionPipeCondition(object):

  """Wrapper around a pipe for usage inside conditions.

  This class contains a POSIX pipe(2) and a poller to poll it. The pipe is

  always allocated when constructing the class. Extra care is taken to always

  close the file descriptors.

  An additional class, L{_SingleActionPipeConditionWaiter}, is used to wait for

  notifications.

  Warning: This class is designed to be used as the underlying component of a

  locking condition, but is not by itself thread safe, and needs to be

  protected by an external lock.

  """

  __slots__ = [

    "_poller",

    "_read_fd",

    "_write_fd",

    "_nwaiters",

    ]

  _waiter_class = _SingleActionPipeConditionWaiter

  def __init__(self):

    """Initializes this class.

    """

    object.__init__(self)

    self._nwaiters = 0

    # Just assume the unpacking is successful, otherwise error handling gets

    # very complicated.

    (self._read_fd, self._write_fd) = os.pipe()

    try:

      # The poller looks for closure of the write side

      poller = select.poll()

      poller.register(self._read_fd, select.POLLHUP)

      self._poller = poller

    except:

      if self._read_fd is not None:

        os.close(self._read_fd)

      if self._write_fd is not None:

        os.close(self._write_fd)

      raise

    # There should be no code here anymore, otherwise the pipe file descriptors

    # may be not be cleaned up properly in case of errors.

  def StartWaiting(self):

    """Return function to wait for notification.

    @rtype: L{_SingleActionPipeConditionWaiter}

    @return: Function to wait for notification

    """

    assert self._nwaiters >= 0

    if self._poller is None:

      raise RuntimeError("Already cleaned up")

    # Create waiter function and increase number of waiters

    wait_fn = self._waiter_class(self, self._poller, self._read_fd)

    self._nwaiters += 1

    return wait_fn

  def DoneWaiting(self):

    """Decrement number of waiters and automatic cleanup.

    Must be called after waiting for a notification.

    @rtype: bool

    @return: Whether this was the last waiter

    """

    assert self._nwaiters > 0

    self._nwaiters -= 1

    if self._nwaiters == 0:

      self._Cleanup()

      return True

    return False

  def notifyAll(self):

    """Close the writing side of the pipe to notify all waiters.

    """

    if self._write_fd is None:

      raise RuntimeError("Can only notify once")

    os.close(self._write_fd)

    self._write_fd = None

  def _Cleanup(self):

    """Close all file descriptors.

    """

    if self._read_fd is not None:

      os.close(self._read_fd)

      self._read_fd = None

    if self._write_fd is not None:

      os.close(self._write_fd)

      self._write_fd = None

    self._poller = None

  def __del__(self):

    """Called on object deletion.

    Ensure no file descriptors are left open.

    """

    self._Cleanup()

class _PipeCondition(_BaseCondition):

  """Group-only non-polling condition with counters.

  This condition class uses pipes and poll, internally, to be able to wait for

  notification with a timeout, without resorting to polling. It is almost

  compatible with Python's threading.Condition, but only supports notifyAll and

  non-recursive locks. As an additional features it's able to report whether

  there are any waiting threads.

  """

  __slots__ = _BaseCondition.__slots__ + [

    "_nwaiters",

    "_pipe",

    ]

  _pipe_class = _SingleActionPipeCondition

  def __init__(self, lock):

    """Initializes this class.

    """

    _BaseCondition.__init__(self, lock)

    self._nwaiters = 0

    self._pipe = None

  def wait(self, timeout=None):

    """Wait for a notification.

    @type timeout: float or None

    @param timeout: Waiting timeout (can be None)

    """

    self._check_owned()

    if not self._pipe:

      self._pipe = self._pipe_class()

    # Keep local reference to the pipe. It could be replaced by another thread

    # notifying while we're waiting.

    pipe = self._pipe

    assert self._nwaiters >= 0

    self._nwaiters += 1

    try:

      # Get function to wait on the pipe

      wait_fn = pipe.StartWaiting()

      try:

        # Release lock while waiting

        self.release()

        try:

          # Wait for notification

          wait_fn(timeout)

        finally:

          # Re-acquire lock

          self.acquire()

      finally:

        # Destroy pipe if this was the last waiter and the current pipe is

        # still the same. The same pipe cannot be reused after cleanup.

        if pipe.DoneWaiting() and pipe == self._pipe:

          self._pipe = None

    finally:

      assert self._nwaiters > 0

      self._nwaiters -= 1

  def notifyAll(self):

    """Notify all currently waiting threads.

    """

    self._check_owned()

    # Notify and forget pipe. A new one will be created on the next call to

    # wait.

    if self._pipe is not None:

      self._pipe.notifyAll()

      self._pipe = None

  def has_waiting(self):

    """Returns whether there are active waiters.

    """

    self._check_owned()

    return bool(self._nwaiters)

class _CountingCondition(object):

  """Wrapper for Python's built-in threading.Condition class.

  This wrapper keeps a count of active waiters. We can't access the internal

  "__waiters" attribute of threading.Condition because it's not thread-safe.

  """

  __slots__ = [

    "_cond",

    "_nwaiters",

    ]

  def __init__(self, lock):

    """Initializes this class.

    """

    object.__init__(self)

    self._cond = threading.Condition(lock=lock)

    self._nwaiters = 0

  def notifyAll(self):

    """Notifies the condition.

    """

    return self._cond.notifyAll()

  def wait(self, timeout=None):

    """Waits for the condition to be notified.

    @type timeout: float or None

    @param timeout: Timeout in seconds

    """

    assert self._nwaiters >= 0

    self._nwaiters += 1

    try:

      return self._cond.wait(timeout=timeout)

    finally:

      self._nwaiters -= 1

  def has_waiting(self):

    """Returns whether there are active waiters.

    """

    return bool(self._nwaiters)

class SharedLock(object):

  """Implements a shared lock.

  Multiple threads can acquire the lock in a shared way, calling

  acquire_shared().  In order to acquire the lock in an exclusive way threads

  can call acquire_exclusive().

  The lock prevents starvation but does not guarantee that threads will acquire

  the shared lock in the order they queued for it, just that they will

  eventually do so.

  """

  __slots__ = [

    "__active_shr_c",

    "__inactive_shr_c",

    "__deleted",

    "__exc",

    "__lock",

    "__pending",

    "__shr",

    ]

  __condition_class = _PipeCondition

  def __init__(self):

    """Construct a new SharedLock.

    """

    object.__init__(self)

    # Internal lock

    self.__lock = threading.Lock()

    # Queue containing waiting acquires

    self.__pending = []

    # Active and inactive conditions for shared locks

    self.__active_shr_c = self.__condition_class(self.__lock)

    self.__inactive_shr_c = self.__condition_class(self.__lock)

    # Current lock holders

    self.__shr = set()

    self.__exc = None

    # is this lock in the deleted state?

    self.__deleted = False

  def __check_deleted(self):

    """Raises an exception if the lock has been deleted.

    """

    if self.__deleted:

      raise errors.LockError("Deleted lock")

  def __is_sharer(self):

    """Is the current thread sharing the lock at this time?

    """

    return threading.currentThread() in self.__shr

  def __is_exclusive(self):

    """Is the current thread holding the lock exclusively at this time?

    """

    return threading.currentThread() == self.__exc

  def __is_owned(self, shared=-1):

    """Is the current thread somehow owning the lock at this time?

    This is a private version of the function, which presumes you're holding

    the internal lock.

    """

    if shared < 0:

      return self.__is_sharer() or self.__is_exclusive()

    elif shared:

      return self.__is_sharer()

    else:

      return self.__is_exclusive()

  def _is_owned(self, shared=-1):

    """Is the current thread somehow owning the lock at this time?

    @param shared:

        - < 0: check for any type of ownership (default)

        - 0: check for exclusive ownership

        - > 0: check for shared ownership

    """

    self.__lock.acquire()

    try:

      return self.__is_owned(shared=shared)

    finally:

      self.__lock.release()

  def _count_pending(self):

    """Returns the number of pending acquires.

    @rtype: int

    """

    self.__lock.acquire()

    try:

      return len(self.__pending)

    finally:

      self.__lock.release()

  def __do_acquire(self, shared):

    """Actually acquire the lock.

    """

    if shared:

      self.__shr.add(threading.currentThread())

    else:

      self.__exc = threading.currentThread()

  def __can_acquire(self, shared):

    """Determine whether lock can be acquired.

    """

    if shared:

      return self.__exc is None

    else:

      return len(self.__shr) == 0 and self.__exc is None

  def __is_on_top(self, cond):

    """Checks whether the passed condition is on top of the queue.

    The caller must make sure the queue isn't empty.

    """

    return self.__pending[0] == cond

  def __acquire_unlocked(self, shared, timeout):

    """Acquire a shared lock.

    @param shared: whether to acquire in shared mode; by default an

        exclusive lock will be acquired

    @param timeout: maximum waiting time before giving up

    """

    self.__check_deleted()

    # We cannot acquire the lock if we already have it

    assert not self.__is_owned(), "double acquire() on a non-recursive lock"

    # Check whether someone else holds the lock or there are pending acquires.

    if not self.__pending and self.__can_acquire(shared):

      # Apparently not, can acquire lock directly.

      self.__do_acquire(shared)

      return True

    if shared:

      wait_condition = self.__active_shr_c

      # Check if we're not yet in the queue

      if wait_condition not in self.__pending:

        self.__pending.append(wait_condition)

    else:

      wait_condition = self.__condition_class(self.__lock)

      # Always add to queue

      self.__pending.append(wait_condition)

    try:

      # Wait until we become the topmost acquire in the queue or the timeout

      # expires.

      while not (self.__is_on_top(wait_condition) and

                 self.__can_acquire(shared)):

        # Wait for notification

        wait_condition.wait(timeout)

        self.__check_deleted()

        # A lot of code assumes blocking acquires always succeed. Loop

        # internally for that case.

        if timeout is not None:

          break

      if self.__is_on_top(wait_condition) and self.__can_acquire(shared):

        self.__do_acquire(shared)

        return True

    finally:

      # Remove condition from queue if there are no more waiters

      if not wait_condition.has_waiting() and not self.__deleted:

        self.__pending.remove(wait_condition)

    return False

  def acquire(self, shared=0, timeout=None):

    """Acquire a shared lock.

    @type shared: int

    @param shared: whether to acquire in shared mode; by default an

        exclusive lock will be acquired

    @type timeout: float

    @param timeout: maximum waiting time before giving up

    """

    self.__lock.acquire()

    try:

      return self.__acquire_unlocked(shared, timeout)

    finally:

      self.__lock.release()

  def release(self):

    """Release a Shared Lock.

    You must have acquired the lock, either in shared or in exclusive mode,

    before calling this function.

    """

    self.__lock.acquire()

    try:

      assert self.__is_exclusive() or self.__is_sharer(), \

        "Cannot release non-owned lock"

      # Autodetect release type

      if self.__is_exclusive():

        self.__exc = None

      else:

        self.__shr.remove(threading.currentThread())

      # Notify topmost condition in queue

      if self.__pending:

        first_condition = self.__pending[0]

        first_condition.notifyAll()

        if first_condition == self.__active_shr_c:

          self.__active_shr_c = self.__inactive_shr_c

          self.__inactive_shr_c = first_condition

    finally:

      self.__lock.release()

  def delete(self, timeout=None):

    """Delete a Shared Lock.

    This operation will declare the lock for removal. First the lock will be

    acquired in exclusive mode if you don't already own it, then the lock

    will be put in a state where any future and pending acquire() fail.

    @type timeout: float

    @param timeout: maximum waiting time before giving up

    """

    self.__lock.acquire()

    try:

      assert not self.__is_sharer(), "Cannot delete() a lock while sharing it"

      self.__check_deleted()

      # The caller is allowed to hold the lock exclusively already.

      acquired = self.__is_exclusive()

      if not acquired:

        acquired = self.__acquire_unlocked(0, timeout)

        assert self.__is_exclusive() and not self.__is_sharer(), \

          "Lock wasn't acquired in exclusive mode"

      if acquired:

        self.__deleted = True

        self.__exc = None

        # Notify all acquires. They'll throw an error.

        while self.__pending:

          self.__pending.pop().notifyAll()

      return acquired

    finally:

      self.__lock.release()

# Whenever we want to acquire a full LockSet we pass None as the value

# to acquire.  Hide this behind this nicely named constant.

ALL_SET = None

class LockSet:

  """Implements a set of locks.

  This abstraction implements a set of shared locks for the same resource type,

  distinguished by name. The user can lock a subset of the resources and the

  LockSet will take care of acquiring the locks always in the same order, thus

  preventing deadlock.

  All the locks needed in the same set must be acquired together, though.

  """

  def __init__(self, members=None):

    """Constructs a new LockSet.

    @param members: initial members of the set

    """

    # Used internally to guarantee coherency.

    self.__lock = SharedLock()

    # The lockdict indexes the relationship name -> lock

    # The order-of-locking is implied by the alphabetical order of names

    self.__lockdict = {}

    if members is not None:

      for name in members:

        self.__lockdict[name] = SharedLock()

    # The owner dict contains the set of locks each thread owns. For

    # performance each thread can access its own key without a global lock on

    # this structure. It is paramount though that *no* other type of access is

    # done to this structure (eg. no looping over its keys). *_owner helper

    # function are defined to guarantee access is correct, but in general never

    # do anything different than __owners[threading.currentThread()], or there

    # will be trouble.

    self.__owners = {}

  def _is_owned(self):

    """Is the current thread a current level owner?"""

    return threading.currentThread() in self.__owners

  def _add_owned(self, name=None):

    """Note the current thread owns the given lock"""

    if name is None:

      if not self._is_owned():

        self.__owners[threading.currentThread()] = set()

    else:

      if self._is_owned():

        self.__owners[threading.currentThread()].add(name)

      else:

        self.__owners[threading.currentThread()] = set([name])

  def _del_owned(self, name=None):

    """Note the current thread owns the given lock"""

    if name is not None:

      self.__owners[threading.currentThread()].remove(name)

    # Only remove the key if we don't hold the set-lock as well

    if (not self.__lock._is_owned() and

        not self.__owners[threading.currentThread()]):

      del self.__owners[threading.currentThread()]

  def _list_owned(self):

    """Get the set of resource names owned by the current thread"""

    if self._is_owned():

      return self.__owners[threading.currentThread()].copy()

    else:

      return set()

  def __names(self):