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

David Daney
2013-07-19T01:17:53Z

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