Good point to raise, Alfredo. Tim – were you referring to this? * Delete callback associated with communicators gets called when communicator is freed * Consider finalize-delete-callback (this is what Alfredo is alluding to perhaps w.r.t datatype-attached-to-environment) – that seems to rely on MPI_COMM_SELF callback (freeing comm-self triggers callback) -- Sayan Ghosh Computer Scientist Future Computing Technologies Group Pacific Northwest National Laboratory (509)-372-6323 • https://urldefense.us/v3/__https://sg0.github.io__;!!G_uCfscf7eWS!dDshRCeikL... From: mpiwg-languages <[email protected]> on behalf of Alfredo Correa via mpiwg-languages <[email protected]> Date: Friday, April 25, 2025 at 1:45 PM To: [email protected] <[email protected]>, [email protected] <[email protected]> Cc: Alfredo Correa <[email protected]> Subject: [mpiwg-languages] static datatypes lifetimes Check twice before you click! This email originated from outside PNNL. Hi Tim, the other day you mention that you played with attaching datatypes (specifically static data types) as keyvalues. This is very interesting. The first thing I notice is that these datatypes will not be global, which is good. but it also ZjQcmQRYFpfptBannerStart This Message Is From an External Sender This message came from outside your organization. ZjQcmQRYFpfptBannerEnd Hi Tim, the other day you mention that you played with attaching datatypes (specifically static data types) as keyvalues. This is very interesting. The first thing I notice is that these datatypes will not be global, which is good. but it also means that they are attached to communicators, not the MPI environment. Am I correct? This would solve the problem of freeing datatypes on program exit. This is different from the idea of attaching it to environment that I was mentioning, but it is possible that attaching it to the communicator is actually a better idea. At the very least, because MPI has a mechanism to “attach” stuff to communicators, but not to the environment.