cancellationToken

CancellationToken is a value type used in many programming environments to propagate a cancellation request for an operation. It enables cooperative cancellation of synchronous and asynchronous work by providing a shared signal that code can observe. A token by itself does not perform cancellation; it represents the possibility of canceling and must be used in conjunction with a cancellation source.

CancellationTokenSource is the component that issues cancellation. Calling Cancel on the source signals all tokens associated with that source. Tokens are obtained from the source via the Token property, and CancellationToken.None represents a non-cancelable token. Tokens can also be combined with linked sources using CreateLinkedTokenSource to respond to multiple cancellation conditions.

Usage typically involves passing a cancellation token to methods that support it. Inside the method, code should periodically check token.IsCancellationRequested or call token.ThrowIfCancellationRequested, which throws an OperationCanceledException to unwind the operation. Tasks and async methods can observe cancellation by propagating the exception or by honoring the token in cooperative operations such as Task.Delay or I/O operations.

Registration allows code to register a callback to run when cancellation is requested. The registration is disposable, so it can be unregistered if the operation completes normally.

Semantics and best practices: cancellation is cooperative and asynchronous; it does not forcibly terminate threads. Tokens are cheap to copy, and multiple tokens from the same source observe the same cancellation signal. Use cancellation tokens to enable responsive shutdown of long-running work, propagate tokens through method boundaries, and compose multiple cancellation conditions via linked tokens.