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Adds APIs to jsg::Lock to perform manual external memory accounting. #2494
Adds APIs to jsg::Lock to perform manual external memory accounting. #2494
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I think this API is error-prone: it's too easy to adjust the memory up and forget to adjust it back down later.
Could we create an RAII-based API instead? Have this method return some sort of an object whose destructor adjusts the memory back down. The object could also have a method to modify the amount of memory it's representing, for cases where we're tracking memory for a data structure that changes over time.
I think this object can just be a trivial wrapper around an integer; no allocation required. It can have a move constructor which zeros out the old value.
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Oh, I missed that this PR actually introduces an RAII API as well.
I think we should only offer the RAII API. We can extend it to work well even when the memory allocation changes over time, using the technique I suggested. Also can avoid the need for a heap allocation.
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Review note: Obviously this can be a problem if the
kj::Own<void>
for this is held beyond the lifespan of theisolate
. Should we include more protections against that by making theisolate
effectively a weak ref rather than a bare pointer? Should we forgo this entirely in favor of just having the manualadjustExternalMemory(...)
call?The key use case for this would be to allow for something like..
Such that the external memory will be automatically adjusted in the isolate when the array is freed. This, of course, is only really appropriate if the array does not get bound to an
ArrayBuffer
at any point, which would cause the data to be double accounted.