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Cancellation
Amp provides primitives to allow the cancellation of operations, namely CancellationTokenSource and CancellationToken.
Every operation that supports cancellation accepts an instance of CancellationToken as (optional) argument. The operation then subscribes with CancellationToken::subscribe() to any cancellation requests that might happen. If the operation consists of any sub-operations that support cancellation, it passes that same CancellationToken instance down to these sub-operations.
The original caller creates a CancellationToken by creating an instance of CancellationTokenSource and passing $cancellationTokenSource->getToken() to the operation. Only the original caller has access to the CancellationTokenSource and can cancel the operation using CancellationTokenSource::cancel().
{:.note}
Cancellations are advisory only and have don't care semantics. A DNS resolver might ignore cancellation requests after the query has been sent as the response has to be processed anyway and can still be cached. An HTTP client might continue a nearly finished HTTP request to reuse the connection, but might abort a chunked encoding response as it cannot know the end.