Running tasks until a condition is true

[zopsicle]

A third party library requires me to implement an interface for it to submit jobs to run in parallel. It looks like this:

class JobSystem
{
public:
    virtual void QueueJob(Job*) = 0;
    virtual void WaitForJobs() = 0;
};

I would like to implement this interface on top of Rayon, as I already use Rayon for unrelated parallel work and they can use the same thread pool.

QueueJob can simply call rayon_core::spawn.

WaitForJobs must block until the jobs submitted by QueueJob all finish, but if this is called from a Rayon thread then it will starve the Rayon thread. It would be better if WaitForJobs runs Rayon tasks if it is called from a Rayon thread. Is there a way to dequeue and run pending Rayon tasks until a condition is true? I found rayon_core::current_thread_has_pending_tasks but it merely returns whether there are any pending tasks.

As far as I understand, rayon_core::scope does run tasks while waiting after its callback returns. If only the scope could be managed explicitly, I could create the scope before any calls to QueueJob, and drop the scope inside WaitForJobs.

[zopsicle]

Apparently rayon_core::yield_now exists. Calling it in a loop until the jobs are done should do the trick. If it returns Yield::Idle then wait for the jobs to finish with a small timeout.