OT Instance creation for multi instance

[BitFis]

Hello,

I was curious about the reasoning for the otInstanceInit(aBuf, aLen) function. What is the benefit for providing the memory from outside during initialisation instead of calling just otPlatCAlloc internally. I am quite curious if there was an acutal use case which created a benefit.

Going through the history, when the init function was provided, there was no calloc function available, so that made sense (https://github.com/openthread/openthread/tree/ffbe65c6ddfaa385f4028e9c85fbc46507dfcfbc/).
But later, it looked like there was shortly the init call with an internal calloc call available, seemingly for a windows adaption. But this got removed. (74a95f0#diff-ec6274e9d4b1f741e41b679089675898c64b8a1644a0546a5010ef13fcb7bce5R233)

Thank you for the explanation.

[abtink]

am quite curious if there was an acutal use case which created a benefit.

The idea is to keep the API flexible and allow each platform to do what they want (use heap-allocated buffer, static allocation, pool-based allocation, etc.).

As an example, the existing code already provides OPENTHREAD_CONFIG_MULTIPLE_STATIC_INSTANCE_ENABLE where the otInstance objects are from a static array up to OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_NUM entries.