Srinath Kailasa

I've tried the following, and it appears to work ```rust mpi::request::multiple_scope(nreqs as usize, |scope, coll| { for (i, packet) in packets.iter().enumerate() { let sreq = world .process_at_rank(packet_destinations[i]) .immediate_send(scope, &packet[..]); coll.add(sreq);...

~~The second error seems to be something to do with sending packets of size 0, and attempting to insert into buffers initialized with 0 length.~~ Actually, still appearing, not sure...

Playing with this example more, it seems to only occur on my Arm M1 Mac (running openmpi 4.0, will try MPICH now), the code runs fine on Ubuntu 20.04 with...

> You may want to take a look at the workarounds discussed at [open-mpi/ompi#8531](https://github.com/open-mpi/ompi/issues/8531) I tried the tmpdir workaround but I'm getting the same error.

I'm attempting to do this, but getting the error that, ``` | |_________^ `*mut fftw_sys::fftw_plan_s` cannot be shared between threads safely``` As plans don't implement Sync, required by rayon's parallel...