Internal and External truncation conditions (original) (raw)

Remi Forax forax at univ-mlv.fr
Sun Feb 10 09:33:24 PST 2013

On 02/10/2013 03:42 PM, Doug Lea wrote:

On 02/10/13 09:28, Remi Forax wrote:

yes, you can it's exactly what j.l.i.SwitchPoint does. Note that we can't transform the whole pipeline to a method handle tree because we have no loopy method handle now, but if we have that, you can create a method handle tree corresponding to the pipeline and when the code will be JITed, with the new lambda form it will, the check will disappear and if a user calls cancl, the JITed code will be trashed and the execution will go back into the interpreter that will do the check.

Which amounts to, at best, an approximation of the rare-trap mechanics that would be used for explicit check in user code if the handles are fully resolved?

It depends what handles fully resolved mean and how the loopy method handle is implemented. If it's implemented like OSR, there is a check when interpreting the code just before doing the backward jump. When JITed, there is no supplementary cost because the JIT has to insert a GC safepoint check (a read to a well known page) and the cancellation mechanism can re-use the very same read.

-Doug

Rémi

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