Tasks & Jobs
Tasks
A Task is a well defined unit of work. Well defined means that all the information that could be required to complete the Task is explicitly contianed or precisely implied by the Task.
Tasks have 2 parts: an Operation and an Input. Operation refers to one of a small number of built in operators. Here are some example Operations
glfs.placeglfs.pickimport.fromURLwasm.wasip1qemu.amd64_microvm
This list is not exhausted, but there are only around a dozen of them.
Input is small payload of bytes. In practice this is a Ref, which references a filesystem to perform the operation on.
These 2 components are included in a hash which becomes the TaskID.
The TaskID is used as key for looking up the result of Task. Want caches the output of Tasks when they are successfully completed, and checks this cache before computing a Task.
An immediate rerun of want build without any changes will result in all the same Tasks, which can all be skipped.
Jobs
Jobs are used to track running computations in Want.
Jobs are created to compute Tasks. Jobs contain active state like whether they have completed and the start and end time.
Jobs are organized into a forest of hierarchical trees. All the major operations in Want create a new tree in the forrest, which is a "root" Job. That job may spawn additional child Jobs.
Child Jobs give computations access to additional compute, since the Child Jobs are computed in parallel. Child Jobs also present a way for Jobs to utilize the cache, which further benefits performance.
Jobs are unable to spawn root or sibling Jobs, they can only spawn Jobs which are their immediate children. This structuring prevents runaway computations. Every new Job has an audit trail, which ultimately goes back to the User asking for something to be done.