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from threading import RLock
from typing import Optional
from reactivex.abc import DisposableBase
class SingleAssignmentDisposable(DisposableBase):
"""Single assignment disposable.
Represents a disposable resource which only allows a single
assignment of its underlying disposable resource. If an underlying
disposable resource has already been set, future attempts to set the
underlying disposable resource will throw an Error."""
def __init__(self) -> None:
"""Initializes a new instance of the SingleAssignmentDisposable
class.
"""
self.is_disposed: bool = False
self.current: Optional[DisposableBase] = None
self.lock = RLock()
super().__init__()
def get_disposable(self) -> Optional[DisposableBase]:
return self.current
def set_disposable(self, value: DisposableBase) -> None:
if self.current:
raise Exception("Disposable has already been assigned")
with self.lock:
should_dispose = self.is_disposed
if not should_dispose:
self.current = value
if self.is_disposed and value:
value.dispose()
disposable = property(get_disposable, set_disposable)
def dispose(self) -> None:
"""Sets the status to disposed"""
old: Optional[DisposableBase] = None
with self.lock:
if not self.is_disposed:
self.is_disposed = True
old = self.current
self.current = None
if old is not None:
old.dispose()
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