[c++-pthreads] thread-safety definition

[Richard Henderson]

On Thu, Jan 08, 2004 at 03:43:52PM +0100, Alexander Terekhov wrote:
> C++ aside for a moment, I have yet to see async-cancel-UNsafe 
> implementation of, say, strlen(). Care to inspire me? TIA.

I have yet to see an async-safe exception runtime.  It's certainly
possible, but it requires the addition of lots of memory barriers
to the code.  Which no one adds because all C++ exceptions are
synchronous [1].  Even Java exceptions are synchronous; the times
that they begin propagation from signal handlers are all
synchronous signals like SIGSEGV or SIGFPE, and the compiler
knows which instructions might produce them.

Thus I believe you will find that async cancelation does *not*
actually invoke cleanup handlers in existing implementations.


r~


[1] Ada exceptions are async, but that language explicitly denys some
of the data availability guarantees that other languages make, which
allows you to avoid the memory barriers.