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# -*- test-case-name: twisted.application.runner.test.test_pidfile -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
PID file.
"""
import errno
from os import getpid, kill, name as SYSTEM_NAME
from types import TracebackType
from typing import Optional, Type
from zope.interface import Interface, implementer
from twisted.logger import Logger
from twisted.python.filepath import FilePath
class IPIDFile(Interface):
"""
Manages a file that remembers a process ID.
"""
def read() -> int:
"""
Read the process ID stored in this PID file.
@return: The contained process ID.
@raise NoPIDFound: If this PID file does not exist.
@raise EnvironmentError: If this PID file cannot be read.
@raise ValueError: If this PID file's content is invalid.
"""
def writeRunningPID() -> None:
"""
Store the PID of the current process in this PID file.
@raise EnvironmentError: If this PID file cannot be written.
"""
def remove() -> None:
"""
Remove this PID file.
@raise EnvironmentError: If this PID file cannot be removed.
"""
def isRunning() -> bool:
"""
Determine whether there is a running process corresponding to the PID
in this PID file.
@return: True if this PID file contains a PID and a process with that
PID is currently running; false otherwise.
@raise EnvironmentError: If this PID file cannot be read.
@raise InvalidPIDFileError: If this PID file's content is invalid.
@raise StalePIDFileError: If this PID file's content refers to a PID
for which there is no corresponding running process.
"""
def __enter__() -> "IPIDFile":
"""
Enter a context using this PIDFile.
Writes the PID file with the PID of the running process.
@raise AlreadyRunningError: A process corresponding to the PID in this
PID file is already running.
"""
def __exit__(
excType: Optional[Type[BaseException]],
excValue: Optional[BaseException],
traceback: Optional[TracebackType],
) -> Optional[bool]:
"""
Exit a context using this PIDFile.
Removes the PID file.
"""
@implementer(IPIDFile)
class PIDFile:
"""
Concrete implementation of L{IPIDFile}.
This implementation is presently not supported on non-POSIX platforms.
Specifically, calling L{PIDFile.isRunning} will raise
L{NotImplementedError}.
"""
_log = Logger()
@staticmethod
def _format(pid: int) -> bytes:
"""
Format a PID file's content.
@param pid: A process ID.
@return: Formatted PID file contents.
"""
return f"{int(pid)}\n".encode()
def __init__(self, filePath: FilePath) -> None:
"""
@param filePath: The path to the PID file on disk.
"""
self.filePath = filePath
def read(self) -> int:
pidString = b""
try:
with self.filePath.open() as fh:
for pidString in fh:
break
except OSError as e:
if e.errno == errno.ENOENT: # No such file
raise NoPIDFound("PID file does not exist")
raise
try:
return int(pidString)
except ValueError:
raise InvalidPIDFileError(
f"non-integer PID value in PID file: {pidString!r}"
)
def _write(self, pid: int) -> None:
"""
Store a PID in this PID file.
@param pid: A PID to store.
@raise EnvironmentError: If this PID file cannot be written.
"""
self.filePath.setContent(self._format(pid=pid))
def writeRunningPID(self) -> None:
self._write(getpid())
def remove(self) -> None:
self.filePath.remove()
def isRunning(self) -> bool:
try:
pid = self.read()
except NoPIDFound:
return False
if SYSTEM_NAME == "posix":
return self._pidIsRunningPOSIX(pid)
else:
raise NotImplementedError(f"isRunning is not implemented on {SYSTEM_NAME}")
@staticmethod
def _pidIsRunningPOSIX(pid: int) -> bool:
"""
POSIX implementation for running process check.
Determine whether there is a running process corresponding to the given
PID.
@param pid: The PID to check.
@return: True if the given PID is currently running; false otherwise.
@raise EnvironmentError: If this PID file cannot be read.
@raise InvalidPIDFileError: If this PID file's content is invalid.
@raise StalePIDFileError: If this PID file's content refers to a PID
for which there is no corresponding running process.
"""
try:
kill(pid, 0)
except OSError as e:
if e.errno == errno.ESRCH: # No such process
raise StalePIDFileError("PID file refers to non-existing process")
elif e.errno == errno.EPERM: # Not permitted to kill
return True
else:
raise
else:
return True
def __enter__(self) -> "PIDFile":
try:
if self.isRunning():
raise AlreadyRunningError()
except StalePIDFileError:
self._log.info("Replacing stale PID file: {log_source}")
self.writeRunningPID()
return self
def __exit__(
self,
excType: Optional[Type[BaseException]],
excValue: Optional[BaseException],
traceback: Optional[TracebackType],
) -> None:
self.remove()
return None
@implementer(IPIDFile)
class NonePIDFile:
"""
PID file implementation that does nothing.
This is meant to be used as a "active None" object in place of a PID file
when no PID file is desired.
"""
def __init__(self) -> None:
pass
def read(self) -> int:
raise NoPIDFound("PID file does not exist")
def _write(self, pid: int) -> None:
"""
Store a PID in this PID file.
@param pid: A PID to store.
@raise EnvironmentError: If this PID file cannot be written.
@note: This implementation always raises an L{EnvironmentError}.
"""
raise OSError(errno.EPERM, "Operation not permitted")
def writeRunningPID(self) -> None:
self._write(0)
def remove(self) -> None:
raise OSError(errno.ENOENT, "No such file or directory")
def isRunning(self) -> bool:
return False
def __enter__(self) -> "NonePIDFile":
return self
def __exit__(
self,
excType: Optional[Type[BaseException]],
excValue: Optional[BaseException],
traceback: Optional[TracebackType],
) -> None:
return None
nonePIDFile: IPIDFile = NonePIDFile()
class AlreadyRunningError(Exception):
"""
Process is already running.
"""
class InvalidPIDFileError(Exception):
"""
PID file contents are invalid.
"""
class StalePIDFileError(Exception):
"""
PID file contents are valid, but there is no process with the referenced
PID.
"""
class NoPIDFound(Exception):
"""
No PID found in PID file.
"""
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