# Copyright Spack Project Developers. See COPYRIGHT file for details.
#
# SPDX-License-Identifier: (Apache-2.0 OR MIT)
import errno
import os
import socket
import sys
import time
from datetime import datetime
from types import TracebackType
from typing import IO, Callable, Dict, Generator, Optional, Tuple, Type
from spack.llnl.util import lang, tty
from ..string import plural
if sys.platform != "win32":
import fcntl
__all__ = [
"Lock",
"LockDowngradeError",
"LockUpgradeError",
"LockTransaction",
"WriteTransaction",
"ReadTransaction",
"LockError",
"LockTimeoutError",
"LockPermissionError",
"LockROFileError",
"CantCreateLockError",
]
ExitFnType = Callable[
[Optional[Type[BaseException]], Optional[BaseException], Optional[TracebackType]],
Optional[bool],
]
ReleaseFnType = Optional[Callable[[], Optional[bool]]]
DevIno = Tuple[int, int] # (st_dev, st_ino) from os.stat_result
def true_fn() -> bool:
"""A function that always returns True."""
return True
class OpenFile:
"""Record for keeping track of open lockfiles (with reference counting)."""
__slots__ = ("fh", "key", "refs")
def __init__(self, fh: IO[bytes], key: DevIno):
self.fh = fh
self.key = key # (dev, ino)
self.refs = 0
class OpenFileTracker:
"""Track open lockfiles by inode, to minimize the number of open file descriptors.
``fcntl`` locks are associated with an inode. If a process closes *any* file descriptor for an
inode, all fcntl locks the process holds on that inode are released, even if other descriptors
for the same inode are still open.
To avoid accidentally dropping locks we keep at most one open file descriptor per inode and
reference-count it. The descriptor is only closed when the reference count reaches zero (i.e.
no ``Lock`` in this process still needs it).
Descriptors are *not* released on unlock; they are kept alive across lock/unlock cycles so that
the next lock operation can skip re-opening the file. ``Lock._ensure_valid_handle``
re-validates the on-disk inode before each lock operation and drops a stale descriptor when
the file was deleted and replaced.
"""
def __init__(self):
self._descriptors: Dict[DevIno, OpenFile] = {}
def get_ref_for_inode(self, key: DevIno) -> Optional[OpenFile]:
"""Fast lookup: do we already have this inode open?"""
return self._descriptors.get(key)
def create_and_track(self, path: str) -> OpenFile:
"""Slow path: Open file, handle directory creation, track it."""
# Open the file and create it if it doesn't exist (incl. directories).
try:
try:
fd = os.open(path, os.O_RDWR | os.O_CREAT)
mode = "rb+"
except PermissionError:
fd = os.open(path, os.O_RDONLY)
mode = "rb"
except OSError as e:
if e.errno != errno.ENOENT:
raise
# Directory missing, create and retry
try:
os.makedirs(os.path.dirname(path), exist_ok=True)
fd = os.open(path, os.O_RDWR | os.O_CREAT)
except OSError:
raise CantCreateLockError(path)
mode = "rb+"
# Get file identifier (device, inode) for tracking.
stat = os.fstat(fd)
key = (stat.st_dev, stat.st_ino)
# Did we open a file we already track, e.g. a symlink to existing tracker file.
if key in self._descriptors:
os.close(fd)
existing = self._descriptors[key]
existing.refs += 1
return existing
# Track the new file.
fh = os.fdopen(fd, mode)
obj = OpenFile(fh, key)
obj.refs += 1
self._descriptors[key] = obj
return obj
def release(self, open_file: OpenFile):
"""Decrement the reference count and close the file handle when it reaches zero."""
open_file.refs -= 1
if open_file.refs <= 0:
if self._descriptors.get(open_file.key) is open_file:
del self._descriptors[open_file.key]
open_file.fh.close()
def purge(self):
"""Close all tracked file descriptors and clear the cache."""
for open_file in self._descriptors.values():
open_file.fh.close()
self._descriptors.clear()
#: Open file descriptors for locks in this process. Used to prevent one process
#: from opening the sam file many times for different byte range locks
FILE_TRACKER = OpenFileTracker()
def _attempts_str(wait_time, nattempts):
# Don't print anything if we succeeded on the first try
if nattempts <= 1:
return ""
attempts = plural(nattempts, "attempt")
return " after {} and {}".format(lang.pretty_seconds(wait_time), attempts)
class LockType:
READ = 0
WRITE = 1
@staticmethod
def to_str(tid):
ret = "READ"
if tid == LockType.WRITE:
ret = "WRITE"
return ret
@staticmethod
def to_module(tid):
lock = fcntl.LOCK_SH
if tid == LockType.WRITE:
lock = fcntl.LOCK_EX
return lock
@staticmethod
def is_valid(op: int) -> bool:
return op == LockType.READ or op == LockType.WRITE
[docs]
class Lock:
"""This is an implementation of a filesystem lock using Python's lockf.
In Python, ``lockf`` actually calls ``fcntl``, so this should work with any filesystem
implementation that supports locking through the fcntl calls. This includes distributed
filesystems like Lustre (when flock is enabled) and recent NFS versions.
Note that this is for managing contention over resources *between* processes and not for
managing contention between threads in a process: the functions of this object are not
thread-safe. A process also must not maintain multiple locks on the same file (or, more
specifically, on overlapping byte ranges in the same file).
"""
def __init__(
self,
path: str,
*,
start: int = 0,
length: int = 0,
default_timeout: Optional[float] = None,
debug: bool = False,
desc: str = "",
) -> None:
"""Construct a new lock on the file at ``path``.
By default, the lock applies to the whole file. Optionally, caller can specify a byte
range beginning ``start`` bytes from the start of the file and extending ``length`` bytes
from there.
This exposes a subset of fcntl locking functionality. It does not currently expose the
``whence`` parameter -- ``whence`` is always ``os.SEEK_SET`` and ``start`` is always
evaluated from the beginning of the file.
Args:
path: path to the lock
start: optional byte offset at which the lock starts
length: optional number of bytes to lock
default_timeout: seconds to wait for lock attempts, where None means to wait
indefinitely
debug: debug mode specific to locking
desc: optional debug message lock description, which is helpful for distinguishing
between different Spack locks.
"""
self.path = path
self._reads = 0
self._writes = 0
self._file_ref: Optional[OpenFile] = None
self._cached_key: Optional[DevIno] = None
# byte range parameters
self._start = start
self._length = length
# enable debug mode
self.debug = debug
# optional debug description
self.desc = f" ({desc})" if desc else ""
# If the user doesn't set a default timeout, or if they choose
# None, 0, etc. then lock attempts will not time out (unless the
# user sets a timeout for each attempt)
self.default_timeout = default_timeout or None
# PID and host of lock holder (only used in debug mode)
self.pid: Optional[int] = None
self.old_pid: Optional[int] = None
self.host: Optional[str] = None
self.old_host: Optional[str] = None
def _ensure_valid_handle(self) -> IO[bytes]:
"""Return a valid file handle for the lock file, opening or re-opening as needed.
On the happy path this costs a single ``os.stat`` syscall: if the inode on disk matches
``_cached_key``, the already-open file handle is returned immediately.
If the inode changed (the lock file was deleted and replaced by another process), the stale
reference is released and a fresh one is obtained. If the file does not exist yet it is
created (along with any missing parent directories).
"""
try:
# Check what is currently on disk. This is the only syscall in the happy path.
stat_res = os.stat(self.path)
current_key = (stat_res.st_dev, stat_res.st_ino)
# Double-check that our cache corresponds the file on disk.
if self._file_ref and not self._file_ref.fh.closed:
if self._cached_key == current_key:
return self._file_ref.fh
# Stale path: file was deleted and replaced on disk.
FILE_TRACKER.release(self._file_ref)
self._file_ref = None
# Get reference to the verified inode from the tracker if it exist, or a new one.
existing_ref = FILE_TRACKER.get_ref_for_inode(current_key)
if existing_ref:
self._file_ref = existing_ref
self._file_ref.refs += 1
else:
# We don't have it tracked, so we need to open and track it ourselves.
self._file_ref = FILE_TRACKER.create_and_track(self.path)
except OSError as e:
# Re-raise all errors except for "file not found".
if e.errno != errno.ENOENT:
raise
# File was not found, so remove it from our cache.
if self._file_ref:
FILE_TRACKER.release(self._file_ref)
self._file_ref = None
self._file_ref = FILE_TRACKER.create_and_track(self.path)
# Update our local cache of what we hold
self._cached_key = self._file_ref.key
return self._file_ref.fh
@staticmethod
def _poll_interval_generator(
_wait_times: Optional[Tuple[float, float, float]] = None,
) -> Generator[float, None, None]:
"""This implements a backoff scheme for polling a contended resource by suggesting a
succession of wait times between polls.
It suggests a poll interval of .1s until 2 seconds have passed, then a poll interval of
.2s until 10 seconds have passed, and finally (for all requests after 10s) suggests a poll
interval of .5s.
This doesn't actually track elapsed time, it estimates the waiting time as though the
caller always waits for the full length of time suggested by this function.
"""
num_requests = 0
stage1, stage2, stage3 = _wait_times or (1e-1, 2e-1, 5e-1)
wait_time = stage1
while True:
if num_requests >= 60: # 40 * .2 = 8
wait_time = stage3
elif num_requests >= 20: # 20 * .1 = 2
wait_time = stage2
num_requests += 1
yield wait_time
def __repr__(self) -> str:
"""Formal representation of the lock."""
rep = f"{self.__class__.__name__}("
for attr, value in self.__dict__.items():
rep += f"{attr}={value.__repr__()}, "
return f"{rep.strip(', ')})"
def __str__(self) -> str:
"""Readable string (with key fields) of the lock."""
location = f"{self.path}[{self._start}:{self._length}]"
timeout = f"timeout={self.default_timeout}"
activity = f"#reads={self._reads}, #writes={self._writes}"
return f"({location}, {timeout}, {activity})"
def __getstate__(self):
"""Don't include file handles or counts in pickled state."""
state = self.__dict__.copy()
del state["_file_ref"]
del state["_reads"]
del state["_writes"]
return state
def __setstate__(self, state):
self.__dict__.update(state)
self._file_ref = None
self._reads = 0
self._writes = 0
def _lock(self, op: int, timeout: Optional[float] = None) -> Tuple[float, int]:
"""This takes a lock using POSIX locks (``fcntl.lockf``).
The lock is implemented as a spin lock using a nonblocking call to ``lockf()``.
If the lock times out, it raises a ``LockError``. If the lock is successfully acquired, the
total wait time and the number of attempts is returned.
"""
assert LockType.is_valid(op)
op_str = LockType.to_str(op)
self._log_acquiring("{0} LOCK".format(op_str))
timeout = timeout or self.default_timeout
fh = self._ensure_valid_handle()
if LockType.to_module(op) == fcntl.LOCK_EX and fh.mode == "rb":
# Attempt to upgrade to write lock w/a read-only file.
# If the file were writable, we'd have opened it rb+
raise LockROFileError(self.path)
self._log_debug(
"{} locking [{}:{}]: timeout {}".format(
op_str.lower(), self._start, self._length, lang.pretty_seconds(timeout or 0)
)
)
start_time = time.monotonic()
end_time = float("inf") if not timeout else start_time + timeout
num_attempts = 1
poll_intervals = Lock._poll_interval_generator()
while True:
if self._poll_lock(op):
return time.monotonic() - start_time, num_attempts
if time.monotonic() >= end_time:
break
time.sleep(next(poll_intervals))
num_attempts += 1
raise LockTimeoutError(op, self.path, time.monotonic() - start_time, num_attempts)
def _poll_lock(self, op: int) -> bool:
"""Attempt to acquire the lock in a non-blocking manner. Return whether
the locking attempt succeeds
"""
assert self._file_ref is not None, "cannot poll a lock without the file being set"
fh = self._file_ref.fh.fileno()
module_op = LockType.to_module(op)
try:
# Try to get the lock (will raise if not available.)
fcntl.lockf(fh, module_op | fcntl.LOCK_NB, self._length, self._start, os.SEEK_SET)
# help for debugging distributed locking
if self.debug:
# All locks read the owner PID and host
self._read_log_debug_data()
self._log_debug(
"{0} locked {1} [{2}:{3}] (owner={4})".format(
LockType.to_str(op), self.path, self._start, self._length, self.pid
)
)
# Exclusive locks write their PID/host
if module_op == fcntl.LOCK_EX:
self._write_log_debug_data()
return True
except OSError as e:
# EAGAIN and EACCES == locked by another process (so try again)
if e.errno not in (errno.EAGAIN, errno.EACCES):
raise
return False
def _read_log_debug_data(self) -> None:
"""Read PID and host data out of the file if it is there."""
assert self._file_ref is not None, "cannot read debug log without the file being set"
self.old_pid = self.pid
self.old_host = self.host
self._file_ref.fh.seek(0)
line = self._file_ref.fh.read()
if line:
pid, host = line.decode("utf-8").strip().split(",")
_, _, pid = pid.rpartition("=")
_, _, self.host = host.rpartition("=")
self.pid = int(pid)
def _write_log_debug_data(self) -> None:
"""Write PID and host data to the file, recording old values."""
assert self._file_ref is not None, "cannot write debug log without the file being set"
self.old_pid = self.pid
self.old_host = self.host
self.pid = os.getpid()
self.host = socket.gethostname()
# write pid, host to disk to sync over FS
self._file_ref.fh.seek(0)
self._file_ref.fh.write(f"pid={self.pid},host={self.host}".encode("utf-8"))
self._file_ref.fh.truncate()
self._file_ref.fh.flush()
os.fsync(self._file_ref.fh.fileno())
def _unlock(self) -> None:
"""Releases a lock using POSIX locks (``fcntl.lockf``)
Releases the lock regardless of mode. Note that read locks may be masquerading as write
locks, but this removes either.
"""
assert self._file_ref is not None, "cannot unlock without the file being set"
fcntl.lockf(
self._file_ref.fh.fileno(), fcntl.LOCK_UN, self._length, self._start, os.SEEK_SET
)
self._reads = 0
self._writes = 0
[docs]
def acquire_read(self, timeout: Optional[float] = None) -> bool:
"""Acquires a recursive, shared lock for reading.
Read and write locks can be acquired and released in arbitrary order, but the POSIX lock is
held until all local read and write locks are released.
Returns True if it is the first acquire and actually acquires the POSIX lock, False if it
is a nested transaction.
"""
timeout = timeout or self.default_timeout
if self._reads == 0 and self._writes == 0:
# can raise LockError.
wait_time, nattempts = self._lock(LockType.READ, timeout=timeout)
self._reads += 1
# Log if acquired, which includes counts when verbose
self._log_acquired("READ LOCK", wait_time, nattempts)
return True
else:
# Increment the read count for nested lock tracking
self._reaffirm_lock()
self._reads += 1
return False
[docs]
def acquire_write(self, timeout: Optional[float] = None) -> bool:
"""Acquires a recursive, exclusive lock for writing.
Read and write locks can be acquired and released in arbitrary order, but the POSIX lock
is held until all local read and write locks are released.
Returns True if it is the first acquire and actually acquires the POSIX lock, False if it
is a nested transaction.
"""
timeout = timeout or self.default_timeout
if self._writes == 0:
# can raise LockError.
wait_time, nattempts = self._lock(LockType.WRITE, timeout=timeout)
self._writes += 1
# Log if acquired, which includes counts when verbose
self._log_acquired("WRITE LOCK", wait_time, nattempts)
# return True only if we weren't nested in a read lock.
# TODO: we may need to return two values: whether we got
# the write lock, and whether this is acquiring a read OR
# write lock for the first time. Now it returns the latter.
return self._reads == 0
else:
# Increment the write count for nested lock tracking
self._reaffirm_lock()
self._writes += 1
return False
def _reaffirm_lock(self) -> None:
"""Fork-safety: always re-affirm the lock with one non-blocking attempt. In the same
process, re-locking an already-held byte range succeeds instantly (POSIX). In a forked
child that doesn't own the POSIX lock, the call fails immediately and we raise. Use WRITE
if we hold an exclusive lock so we don't accidentally downgrade it."""
if self._writes > 0:
op = LockType.WRITE
elif self._reads > 0:
op = LockType.READ
else:
return
self._ensure_valid_handle()
if not self._poll_lock(op):
raise LockTimeoutError(op, self.path, time=0, attempts=1)
[docs]
def try_acquire_read(self) -> bool:
"""Non-blocking attempt to acquire a shared read lock.
Returns True if the lock was acquired, False if it would block.
"""
if self._reads == 0 and self._writes == 0:
self._ensure_valid_handle()
if not self._poll_lock(LockType.READ):
return False
self._reads += 1
self._log_acquired("READ LOCK", 0, 1)
return True
else:
self._reaffirm_lock()
self._reads += 1
return True
[docs]
def try_acquire_write(self) -> bool:
"""Non-blocking attempt to acquire an exclusive write lock.
Returns True if the lock was acquired, False if it would block.
"""
if self._writes == 0:
fh = self._ensure_valid_handle()
if LockType.to_module(LockType.WRITE) == fcntl.LOCK_EX and fh.mode == "rb":
raise LockROFileError(self.path)
if not self._poll_lock(LockType.WRITE):
return False
self._writes += 1
self._log_acquired("WRITE LOCK", 0, 1)
return True
else:
self._reaffirm_lock()
self._writes += 1
return True
[docs]
def is_write_locked(self) -> bool:
"""Returns ``True`` if the path is write locked, otherwise, ``False``"""
try:
self.acquire_read()
# If we have a read lock then no other process has a write lock.
self.release_read()
except LockTimeoutError:
# Another process is holding a write lock on the file
return True
return False
[docs]
def downgrade_write_to_read(self, timeout: Optional[float] = None) -> None:
"""Downgrade from an exclusive write lock to a shared read.
Raises:
LockDowngradeError: if this is an attempt at a nested transaction
"""
timeout = timeout or self.default_timeout
if self._writes == 1 and self._reads == 0:
self._log_downgrading()
# can raise LockError.
wait_time, nattempts = self._lock(LockType.READ, timeout=timeout)
self._reads = 1
self._writes = 0
self._log_downgraded(wait_time, nattempts)
else:
raise LockDowngradeError(self.path)
[docs]
def upgrade_read_to_write(self, timeout: Optional[float] = None) -> None:
"""Attempts to upgrade from a shared read lock to an exclusive write.
Raises:
LockUpgradeError: if this is an attempt at a nested transaction
"""
timeout = timeout or self.default_timeout
if self._reads == 1 and self._writes == 0:
self._log_upgrading()
# can raise LockError.
wait_time, nattempts = self._lock(LockType.WRITE, timeout=timeout)
self._reads = 0
self._writes = 1
self._log_upgraded(wait_time, nattempts)
else:
raise LockUpgradeError(self.path)
[docs]
def release_read(self, release_fn: ReleaseFnType = None) -> bool:
"""Releases a read lock.
Arguments:
release_fn: function to call *before* the last recursive lock (read or write) is
released.
If the last recursive lock will be released, then this will call release_fn and return its
result (if provided), or return True (if release_fn was not provided).
Otherwise, we are still nested inside some other lock, so do not call the release_fn and,
return False.
Does limited correctness checking: if a read lock is released when none are held, this
will raise an assertion error.
"""
assert self._reads > 0
locktype = "READ LOCK"
if self._reads == 1 and self._writes == 0:
self._log_releasing(locktype)
# we need to call release_fn before releasing the lock
release_fn = release_fn or true_fn
result = release_fn()
self._unlock() # can raise LockError.
self._reads = 0
self._log_released(locktype)
return bool(result)
else:
self._reads -= 1
return False
[docs]
def release_write(self, release_fn: ReleaseFnType = None) -> bool:
"""Releases a write lock.
Arguments:
release_fn: function to call before the last recursive write is released.
If the last recursive *write* lock will be released, then this will call release_fn and
return its result (if provided), or return True (if release_fn was not provided).
Otherwise, we are still nested inside some other write lock, so do not call the release_fn,
and return False.
Does limited correctness checking: if a read lock is released when none are held, this
will raise an assertion error.
"""
assert self._writes > 0
release_fn = release_fn or true_fn
locktype = "WRITE LOCK"
if self._writes == 1:
self._log_releasing(locktype)
# we need to call release_fn before releasing the lock
result = release_fn()
if self._reads > 0:
self._lock(LockType.READ)
else:
self._unlock() # can raise LockError.
self._writes = 0
self._log_released(locktype)
return bool(result)
else:
self._writes -= 1
return False
[docs]
def cleanup(self) -> None:
if self._reads == 0 and self._writes == 0:
os.unlink(self.path)
else:
raise LockError("Attempting to cleanup active lock.")
def _get_counts_desc(self) -> str:
return (
"(reads {0}, writes {1})".format(self._reads, self._writes) if tty.is_verbose() else ""
)
def _log_acquired(self, locktype, wait_time, nattempts) -> None:
attempts_part = _attempts_str(wait_time, nattempts)
now = datetime.now()
desc = "Acquired at %s" % now.strftime("%H:%M:%S.%f")
self._log_debug(self._status_msg(locktype, "{0}{1}".format(desc, attempts_part)))
def _log_acquiring(self, locktype) -> None:
self._log_debug(self._status_msg(locktype, "Acquiring"), level=3)
def _log_debug(self, *args, **kwargs) -> None:
"""Output lock debug messages."""
kwargs["level"] = kwargs.get("level", 2)
tty.debug(*args, **kwargs)
def _log_downgraded(self, wait_time, nattempts) -> None:
attempts_part = _attempts_str(wait_time, nattempts)
now = datetime.now()
desc = "Downgraded at %s" % now.strftime("%H:%M:%S.%f")
self._log_debug(self._status_msg("READ LOCK", "{0}{1}".format(desc, attempts_part)))
def _log_downgrading(self) -> None:
self._log_debug(self._status_msg("WRITE LOCK", "Downgrading"), level=3)
def _log_released(self, locktype) -> None:
now = datetime.now()
desc = "Released at %s" % now.strftime("%H:%M:%S.%f")
self._log_debug(self._status_msg(locktype, desc))
def _log_releasing(self, locktype) -> None:
self._log_debug(self._status_msg(locktype, "Releasing"), level=3)
def _log_upgraded(self, wait_time, nattempts) -> None:
attempts_part = _attempts_str(wait_time, nattempts)
now = datetime.now()
desc = "Upgraded at %s" % now.strftime("%H:%M:%S.%f")
self._log_debug(self._status_msg("WRITE LOCK", "{0}{1}".format(desc, attempts_part)))
def _log_upgrading(self) -> None:
self._log_debug(self._status_msg("READ LOCK", "Upgrading"), level=3)
def _status_msg(self, locktype: str, status: str) -> str:
status_desc = "[{0}] {1}".format(status, self._get_counts_desc())
return "{0}{1.desc}: {1.path}[{1._start}:{1._length}] {2}".format(
locktype, self, status_desc
)
[docs]
class LockTransaction:
"""Simple nested transaction context manager that uses a file lock.
Arguments:
lock: underlying lock for this transaction to be acquired on enter and released on exit
acquire: function to be called after lock is acquired
release: function to be called before release, with ``(exc_type, exc_value, traceback)``
timeout: number of seconds to set for the timeout when acquiring the lock (default no
timeout)
"""
def __init__(
self,
lock: Lock,
acquire: Optional[Callable[[], None]] = None,
release: Optional[ExitFnType] = None,
timeout: Optional[float] = None,
) -> None:
self._lock = lock
self._timeout = timeout
self._acquire_fn = acquire
self._release_fn = release
def __enter__(self):
if self._enter() and self._acquire_fn:
return self._acquire_fn()
def __exit__(
self,
exc_type: Optional[Type[BaseException]],
exc_value: Optional[BaseException],
traceback: Optional[TracebackType],
) -> bool:
def release_fn():
if self._release_fn is not None:
return self._release_fn(exc_type, exc_value, traceback)
return bool(self._exit(release_fn))
def _enter(self) -> bool:
raise NotImplementedError
def _exit(self, release_fn: ReleaseFnType) -> bool:
raise NotImplementedError
[docs]
class ReadTransaction(LockTransaction):
"""LockTransaction context manager that does a read and releases it."""
def _enter(self):
return self._lock.acquire_read(self._timeout)
def _exit(self, release_fn):
return self._lock.release_read(release_fn)
[docs]
class WriteTransaction(LockTransaction):
"""LockTransaction context manager that does a write and releases it."""
def _enter(self):
return self._lock.acquire_write(self._timeout)
def _exit(self, release_fn):
return self._lock.release_write(release_fn)
[docs]
class LockError(Exception):
"""Raised for any errors related to locks."""
[docs]
class LockDowngradeError(LockError):
"""Raised when unable to downgrade from a write to a read lock."""
def __init__(self, path: str) -> None:
msg = "Cannot downgrade lock from write to read on file: %s" % path
super().__init__(msg)
[docs]
class LockTimeoutError(LockError):
"""Raised when an attempt to acquire a lock times out."""
def __init__(self, lock_type: int, path: str, time: float, attempts: int) -> None:
lock_type_str = LockType.to_str(lock_type).lower()
fmt = "Timed out waiting for a {} lock after {}.\n Made {} {} on file: {}"
super().__init__(
fmt.format(
lock_type_str,
lang.pretty_seconds(time),
attempts,
"attempt" if attempts == 1 else "attempts",
path,
)
)
[docs]
class LockUpgradeError(LockError):
"""Raised when unable to upgrade from a read to a write lock."""
def __init__(self, path: str) -> None:
msg = "Cannot upgrade lock from read to write on file: %s" % path
super().__init__(msg)
[docs]
class LockPermissionError(LockError):
"""Raised when there are permission issues with a lock."""
[docs]
class LockROFileError(LockPermissionError):
"""Tried to take an exclusive lock on a read-only file."""
def __init__(self, path: str) -> None:
msg = "Can't take write lock on read-only file: %s" % path
super().__init__(msg)
[docs]
class CantCreateLockError(LockPermissionError):
"""Attempt to create a lock in an unwritable location."""
def __init__(self, path: str) -> None:
msg = "cannot create lock '%s': " % path
msg += "file does not exist and location is not writable"
super().__init__(msg)