Description
In many cases we want to execute some work that does not play well with Riot's scheduling, that wouldn't play well with work-stealing, that needs to use libraries that don't play well with Riot's IO, or that simply need to aggressively busy-wait to meet certain real-time deadlines (like rendering a frame within 16ms).
For those use-cases, spawn, spawn_pinned, and process_flag (Priority High) are not suitable solutions since they all expect the process to not starve the scheduler, to be friendly to work-stealing, and to use Riot's IO layer.
Instead, we'd like to implement spawn_blocking fn which will create a new process, like any other process, but allocate an entire OS thread to execute it.
The signature of this function would be identical to spawn:
val spanw_blocking : (unit -> unit) -> Pid.tImplementation Notes
To do this, we'd start by adding the signature to the riot.mli file, and working backwards from there until we reach the imports.ml module where spawn and spawn_pinned are defined. This function should probably call into a function like Pool.spawn_blocking that will do the work of setting up a new scheduler just for this process, and updating the list of domains in the global pool variable.
Then we'd want the pool type inside the scheduler.ml module to be extended to include a list of Domains that have been spawned for these blocking processes:
type pool = {
(* ... *)
blocking_processes: unit Domain.t list Atomic.t;
}It is important that we make this list atomic to make sure that multiple processes spawning new blocking processes from different scheduling threads do not override the domain handlers.
The final set of changes could look a little bit like this, but this list is not a set of requirements and other implementations are welcome:
- new
spawn_blockingfunction with its signature and documentation on Riot.mli - new
Pool.spawn_blockingfunction that uses a newBlocking_schedulerin a new Domain - new
blocking_processesattribute on thepooltype to keep track of new domains - new
Blocking_schedulerthat wraps aSchedulerand adds logic for removing the domains from theblocking_processesdomain list
Hope this helps!