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Subject: Re: [boost] Question for C++ experts about exception allocation failure
From: Sebastian Redl (sebastian.redl_at_[hidden])
Date: 2009-05-17 04:53:36

Emil Dotchevski wrote:
> How is failure to allocate an exception object handled in various
> compilers? 15.1.4 says that "the memory for the temporary copy of the
> exception being thrown is allocated in an unspecified way" but I don't
> think it specifies behavior for the case when the allocation fails. I
> know that some compilers allocate exceptions from the heap, so does
> this mean that an attempt to throw any exception could, in theory,
> result in a std::bad_alloc being thrown instead? As far as I can tell
> such behavior wouldn't violate the C++ standard, but I'm not sure my
> interpretation is correct. Anyone?
GCC allocates exceptions on the heap. If that fails, it will allocate
them in the emergency storage instead. The emergency storage is a small
buffer (64 slots of a few kB each - used to be 16 slots, but I changed
that when I implemented exception propagation) allocated statically.
If allocation in emergency storage fails, GCC aborts the process.

The way the common C++ ABI is specified, I think every compiler that
follows it will have to do a very similar thing. There's a
__cxa_allocate_exception function specified. So Sun, IBM and HP's
compilers probably do the same thing. But I can't vouch for it.

MSVC allocates on the stack.


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