Create Basic Job System

[AlexSabourinDev]

Is your feature request related to a problem? Please describe. Ice Box will require a job system for a variety of systems such as rendering, loading and more.

Describe the solution you'd like I expect this job system to have a few features to get started and we can add to it as we discover needs.

• Job chaining - A job should be able to wait until another job is complete.
• Lambdas - Jobs should be easy to create inline making for comfortable ease of use.
• Lightweight - Jobs should not have significant overhead, they should take up minimal memory and scheduling should have minimal overhead.

The approach I suggest is to store a queue per thread and allow for lock free work stealing. (See [1]) A queue per thread will allow the jobs to advance and hopefully allow for a reduced use of atomics and contention.

The API should be simple:

• JobHandle = launchJob(Lambda, Data, JobHandle) - Launches a job at some point in the future and returns a handle to the job request. A JobHandle shouldn't necessarily be defined by a single job. It could also define a set of jobs (See [2]). This would allow a simple API to wait on a group of jobs. The optional JobHandle allows you to wait on a job handle before your job is launched.

Consider not adding a blocking "wait" call until a system requires it. It could hopefully push the system designer to consider not having blocking calls.

For "OnJobComplete" callbacks, consider leaving this to the appropriate system. There is no clear thread where it would be "thread safe" to trigger an OnJobComplete event and as a result it would be much simpler for the owning system to decide how to handle it.

Resources [1] https://blog.molecular-matters.com/tag/job-system/ [2] http://danglingpointers.com/post/job-system/

[AlexSabourinDev]

I'm considering that we can make each worker thread have it's own lock-free job queue. Seems like an interesting and fun challenge.

I'm not sure yet if work stealing is worthwhile. It could be something we can consider in the future.

[AlexSabourinDev]

Split job chaining to issue #22