Fix lint tool cancellation

[doxxx]

When a lint tool takes a non-trivial amount of time to execute (e.g. gometalinter), and the user has lintOnSave enabled, saving a file twice in quick succession causes the previous lint tool execution to be cancelled.

However, subsequent executions of the lint tool will be terminated immediately because the "global" CancellationTokenSource used for cancelling the lint tool is still in the cancelled state.

This is fixed by recreating the CancellationTokenSource after it has been cancelled.

[ramya-rao-a]

Nice catch! Can you do the same in the goVet.ts file for the vetting process?

[doxxx]

It's not clear to me whether I need to wrap the cancel in a try/finally so that the dispose will always be called. I don't know how closely vscode's implementation of CancellationTokenSource mirrors that of .NET's.

[ramya-rao-a]

I spent a long time looking at how the CancellationTokenSource works and came at the below conclusion:

• Yes, like you figured out, once cancelled, the token remains in a cancelled state and every new onCancellationRequest handler will get called
• The token source needs to be disposed after each use. Take the case of a completed lint process followed by a cancelled one. If the token source is not disposed after the first use, then the onCancellationRequest handler will get called even for the completed process

7f8e68d should take care of both cases.

It's not clear to me whether I need to wrap the cancel in a try/finally so that the dispose will always be called.

Are you talking about the case that one of the cancel event handlers might throw an exception and so the dispose won't be called?

[doxxx]

Are you talking about the case that one of the cancel event handlers might throw an exception and so the dispose won't be called?

Yes.

[ramya-rao-a]

Just tried throwing an exception from the cancel event handler. It doesn't affect the dispose. So we are good.