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cudaidiomsnull-pointer

Is cudaFree(0) guaranteed to do anything?

Mark Harris wrote here once - albeit 9 years ago by now - that:

In fact cudaFree(0) is commonly used to initialize the CUDA context!

and I see this (somewhat questionable) idiom used in this example program repository of NVIDIA's, used in presented in this year's GTC.

So, is cudaFree(0) guaranteed to actually do anything?

Solution

  • Formally - no, it isn't guaranteed to do anything.

    Following the sages' comments:

    The documentation, if anything, suggests no action. Empirically, using cudaFree(0), possibly after a cudaSetDevice(), forces the establishment of a context. I would speculate it does something similar to cuDevicePrimaryCtxRetain() (which is what one might use in a naive implementation of cudaFree() using the driver API).