Caches

There are various caches used by the in-tree tasks. This page attempts to document them and their appropriate use.

Caches are essentially isolated filesystems that are persisted between tasks. For example, if 2 tasks run on a worker - one after the other - and both tasks request the same cache, the subsequent task will be able to see files in the cache that were created by the first task. It’s also worth noting that TaskCluster workers ensure a cache can only be used by 1 task at a time. If a worker is simultaneously running multiple tasks requesting the same named cache, the worker will have multiple caches of the same name on the worker.

Caches and run-task

run-task is our generic task wrapper script. It does common activities like ensure a version control checkout is present.

One of the roles of run-task is to verify and sanitize caches. It does this by storing state in a cache on its first use. If the recorded capabilities of an existing cache don’t match expectations for the current task, run-task bails. This ensures that caches are only reused by tasks with similar execution profiles. This prevents accidental cache use across incompatible tasks. It also allows run-task to make assumptions about the state of caches, which can help avoid costly operations.

In addition, the hash of run-task is used to derive the cache name. So any time run-task changes, a new set of caches are used. This ensures that any backwards incompatible changes or bug fixes to run-task result in fresh caches.

Some caches are reserved for use with run-task. That property will be denoted below.

Common Caches

Version Control Caches

level-{{level}}-checkouts-{{hash}}

This cache holds version control checkouts, each in a subdirectory named after the repo (e.g., gecko).

Checkouts should be read-only. If a task needs to create new files from content of a checkout, this content should be written in a separate directory/cache (like a workspace).

This cache name pattern is managed by run-task and must only be used with run-task.

level-{{level}}-checkouts-sparse-{{hash}}
This is like the above but is used when the checkout is sparse (contains a subset of files).
level-{{level}}-checkouts-{{version}} (deprecated)

This cache holds version control checkouts, each in a subdirectory named after the repo (e.g., gecko).

Checkouts should be read-only. If a task needs to create new files from content of a checkout, this content should be written in a separate directory/cache (like a workspace).

A version parameter appears in the cache name to allow backwards-incompatible changes to the cache’s behavior.

The hg-store contains a shared store <https://www.mercurial-scm.org/wiki/ShareExtension> that is is used by hg robustcheckout. If you are using run-task you should set the HG_STORE_PATH environment variable to point to this directory. If you are using hg robustcheckout, pass this directory to the --sharebase option.

Workspace Caches

level-{{level}}-*-workspace
These caches (of various names typically ending with workspace) contain state to be shared between task invocations. Use cases are dependent on the task.

Other

level-{{level}}-tooltool-cache-{{hash}}

Tooltool invocations should use this cache. Tooltool will store files here indexed by their hash.

This cache name pattern is reserved for use with run-task and must only be used by run-task

tooltool-cache (deprecated)
Legacy location for tooltool files. Use the per-level one instead.