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Document number: N3592

Date: 2013-03-15

Alternative Proposal for Cancellation and Exceptions

by Torvald Riegel

Excerpts:

In what follows, I will describe cancellation and data escape mechanisms for transactions as specified by the current draft specification and the changes summarized in N3589. These are supposed to replace the cancellation mechanisms in the current draft (i.e., the __transaction_cancel keyword and the cancel-and-throw functionality). ...

The cancellation mechanisms described here are supposed to serve as a foundation for higher-level features that make use of cancellation, such as composable forms of error recovery or more focused kinds of speculative execution. They also try to provide cancellation with no language extensions or changes (besides a minor extension to the syntax of transaction statements); most of the functionality can be expressed as library features. ...

At first sight, it might look like cancellation and exception handling are more or less the same. I disagree with that, and will briefly argue in what follows that they are sufficiently different to justify having separate mechanisms for both. ...