Re: [RFC / musing] Scoped exception handling in Linux userspace?

From: David Daney
Date: Thu Jul 18 2013 - 21:17:56 EST


On 07/18/2013 05:50 PM, Andy Lutomirski wrote:
On Thu, Jul 18, 2013 at 5:40 PM, David Daney <ddaney.cavm@xxxxxxxxx> wrote:
On 07/18/2013 05:26 PM, Andy Lutomirski wrote:

Windows has a feature that I've wanted on Linux forever: stack-based
(i.e. scoped) exception handling. The upshot is that you can do,
roughly, this (pseudocode):

int callback(...)
{
/* Called if code_that_may_fault faults. May return "unwind to
landing pad", "propagate the fault", or "fixup and retry" */
}

void my_function()
{
__hideous_try_thing(callback) {
code_that_may_fault();
} blahblahblah {
landing_pad_code();
}
}


How is this different than throwing exceptions from a signal handler?

Two ways. First, exceptions thrown from a signal handler can't be
retries.

??

Second, and more importantly, installing a signal handler in
a library is a terrible idea.

The signal handler would be installed by main() before calling into the library. You have to have a small amount of boiler plate code to set it up, but the libraries wouldn't have to be modified if they were already exception safe.

FWIW the libgcj java runtime environment uses this strategy for handling NullPointerExceptions and DivideByZeroError(sp?). Since all that code for the most part follows the standard C++ ABIs, it is an example of this technique that has been deployed in many environments.

David Daney

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