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Android Docs: Elaborate on the purpose of Turbine

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Change-Id: I8cc0870bff7fe3647d3538851235f8322dc87112
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4080646
Reviewed-by: Peter Wen <wnwen@chromium.org>
Commit-Queue: Peter Wen <wnwen@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1079254}
This commit is contained in:
Andrew Grieve
2022-12-05 16:09:06 +00:00
committed by Chromium LUCI CQ
parent 236a643727
commit 49e725ab56
1 changed files with 11 additions and 8 deletions

19
build/android/docs/java_toolchain.md

@ -30,20 +30,23 @@ Most targets produce two separate `.jar` files:
### Step 1: Create interface .jar with turbine or ijar
For prebuilt `.jar` files, use [//third_party/ijar] to create interface `.jar`
from prebuilt `.jar`.
For non-prebuilt targets, use [//third_party/turbine] to create interface `.jar`
from `.java` source files. Turbine is much faster than javac, and so enables
full compilation to happen more concurrently.
What are interface jars?:
* The contain `.class` files with all non-public symbols and function bodies
* They contain `.class` files with all private symbols and all method bodies
removed.
* Dependant targets use interface `.jar` files to skip having to be rebuilt
when only private implementation details change.
For prebuilt `.jar` files: we use [//third_party/ijar] to create interface
`.jar` files from the prebuilt ones.
For non-prebuilt `.jar` files`: we use [//third_party/turbine] to create
interface `.jar` files directly from `.java` source files. Turbine is faster
than javac because it does not compile method bodies. Although Turbine causes
us to compile files twice, it speeds up builds by allowing `javac` compilation
of targets to happen concurrently with their dependencies. We also use Turbine
to run our annotation processors.
[//third_party/ijar]: /third_party/ijar/README.chromium
[//third_party/turbine]: /third_party/turbine/README.chromium