way to control the scheduler

[alkis]

This can allow some usecases:

• for a given coroutine/scope limit parallelism to 1
• pin a coroutine/scope to a specific thread (UI thread for example)

Perhaps this is already possible?

[Xudong-Huang]

for a given coroutine/scope limit parallelism to 1

this is possible with the following configuration

may::config().set_workers(1).set_io_workers(0);

pin a coroutine/scope to a specific thread (UI thread for example)

no, currently may doesn't support coroutine thread affinity.

[alkis]

Wouldn't:

may::config().set_workers(1).set_io_workers(0);

set parallelism to 1 across all coroutines?

What I want to do is to have a function:

fn doStuff() {}

and all coroutines that run through it have constrained parallelism.

[Xudong-Huang]

can Mutex/Semphore fullfill the requirement?

[alkis]

It will do the work but it seems to me that it does more work than necessary.

The scheduler already does the synchronization (fences/etc) necessary when a coroutine switches from one thread to another. If for example it happens that most of the time doStuff() is running with 1 parallelism, having a scheduler constraint will amount to an atomic increment and decrement. Assuming the doStuff() is not contended, this will be super fast.

Mutex seems much heavier than that. Perhaps I am missing something?

[Xudong-Huang]

The sync primitives used in coroutine context doesn't involve system calls, and they are just running in user space which is fast.