On 27/03/2013, at 3:43 PM, Daz DeBoer <[email protected]> wrote:
> G'day
>
> Now in master is a pretty cool new feature: you can now implement an
> 'incremental' task that is informed about exactly which input files
> have changed when the task is out of date.
> This is very useful for something like a C++ compile task, as it means
> that only the changed files need to be recompiled, rather than the
> entire set of inputs.
>
> I've got a 'draft' DSL functioning, and would appreciate any feedback
> you guys have. Here's a sample:
>
> class IncrementalSync extends DefaultTask {
> @InputFiles
> def FileCollection src
>
> @OutputDirectory
> def File destination
>
> @TaskAction
> void execute(TaskInputChanges inputs) {
> if (inputs.allOutOfDate) {
> FileUtils.forceDelete(destination)
> }
>
> inputs.outOfDate({
> FileUtils.copyFile(change.file, targetFile(change.file))
> } as Action)
> .removed({
> FileUtils.forceDelete(targetFile(change.file))
> } as Action)
> .process()
> }
>
> def targetFile(def inputFile) {
> new File(destination, change.file.name)
> }
> }
>
> Notes:
> 1. The way to implement an incremental task is to add a
> TaskInputChanges parameter to your @TaskAction method. This must be a
> typed parameter, and currently TaskInputChanges is the only parameter
> type we support (but there are plans to add more, like
> TaskOutputChanges). The reason for using a typed parameter is that
> this is the way the task tells us what it wants: I thought about an
> annotated parameter, but it seems kind of pointless when the
> annotation would imply the type anyway. (Perhaps we can add an
> annotation-based marker at a later stage, if it helps).
>
> 2. There are 2 discrete ways we report incremental changes:
> - If the _only_ change to the task execution state is changed input
> files, then TaskInputChanges.allOutOfDate() will be false, and only
> the added/changed/removed files will be notified to the
> TaskInputChanges.outOfDate() and .removed() actions.
> - In the case of non-file changes to task inputs (properties, task
> class) and changes to task output files, then Gradle will consider all
> input files to be out of date. In this case,
> TaskInputChanges.allOutOfDate() will be true, and every input file
> will be reported to the TaskInputChanges.outOfDate() action.
>
> 4. The reason for the chained action methods combined with a final
> process() method is that this allows us to stream changed inputs in
> any order, and does not require us to persist these changes for a
> subsequent method call. This is a little awkward, but doesn't force us
> to jump through hoops. We could implement a more discrete API on top,
> but it may be less efficient.
I don't like these methods being on TaskInputChanges. It doesn't make much
sense to me.
I'd prefer something like…
interface TaskInputChanges {
void processing(Action<TaskInputChangesProcessing> action)
}
Where TaskInputChangesProcessing has the outOfDate(Action) etc methods.
This feels better to me. Also frees the user from having to invoke the
processing and gives us more control over when it's invoked if we need it.
>
> 5. I haven't yet got any DSL magic applied to the TaskInputChanges
> instance, so using a closure directly isn't (yet) possible. Not sure
> how important that is for this DSL, or how tricky it will be to add.
I'd say it's a requirement.
>
> You can read more about the plans here:
> https://github.com/gradle/gradle/blob/master/design-docs/incremental-build.md
> Next steps for incremental tasks include providing access to changed
> outputs and properties (in the case a task can handle these more
> efficiently), automatically cleaning up stale outputs, and fixing some
> bugs around the incremental nature of Copy tasks (and others).
This is cool stuff :)
--
Luke Daley
Principal Engineer, Gradleware
http://gradleware.com
Join me at the Gradle Summit 2013, June 13th and 14th in Santa Clara, CA:
http://www.gradlesummit.com
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