Re: Re: [boost] Re: Next revision of boost::thread

From: Peter Dimov (pdimov_at_[hidden])
Date: 2003-01-09 15:59:05

From: "William E. Kempf" <wekempf_at_[hidden]>
>
> OK, I've been looking at boost::filesystem_error.  Here's my thoughts:
>
> boost::filesystem_error could be benefited by splitting it up into more
> exception types.  I know this was suggested in the review, but don't know
> what the plan was in regard to this.  In Boost.Threads case, so far we
have
> need for 4 different errors: lock errors, resource errors, invalid
arguments and
> unsupported errors.

POSIX actually distinguishes out of memory errors (ENOMEM) from other lack
of resource errors (EAGAIN), and POSIX functions can fail with an "access
denied" error (EPERM).

There are also several types of POSIX lock errors (EINVAL, EBUSY, EAGAIN,
EDEADLK, EPERM.) Boost.Threads has two additional lock errors associated
with the Lock concept that have no POSIX equivalent.

> Some have suggested carrying the OS error code, but given only 4 possible
error
> conditions, does this even sound reasonable?

If the reason for the failure can be identified by the type of the
exception, there should be no immediate need to carry an OS error code,
although you should consider the "how do I translate this to a localized
error message" problem.

> Or are people
> suggesting Boost.Threads should use a single exception type and carry the
error
> code, as filesystem_error currently does?

No, this would be a step backward. IIUC filesystem_error is expected to
evolve into a hierarchy as exception categories of interest to callers are
identified.