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C++ exceptions and blobs |
When a blob is used in the context of a PREDICATE()
macro, it can raise a C++ exception (PlFail
or PlException
)
and the
PREDICATE() code will convert
the exception to the appropriate Prolog failure or error; memory
allocation exceptions are also handled.
Blobs have callbacks, which can run outside the context of a PREDICATE(). Their exception handling is as follows:
PlAtom::null
,
which is interpreted by Prolog as failure.false
(or throw a PlException
or
PlExceptinFailBase
, which will be interpreted as a return
value of false
), resulting in the blob not being garbage
collected, and the destructor not being called. Note that this doesn't
work well with final clean-up atom garbage collection, which disregards
the return value and also doesn't respect the ordering of blob
dependencies (e.g., if an iterator blob refers to a file-like blob, the
file-like blob might be deleted before the iterator is deleted).
This code runs in the gc
thread. The only PL_*()
function that can safely be called are
PL_unregister_atom() (which is what PlAtom::unregister_ref()
calls).