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Android library for building pipelines for executing background tasks
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udeyrishi/pipe
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Pipe is an Android library for building pipelines for executing background tasks.
- Declarative: Uses a Kotlin DSL or builder to declare pipeline schematics.
- Powerful: Supports both simple steps and complex synchronization structures like barriers and aggregators.
- Resilient: Pipe has resiliency baked-in. Has support for step retries in case of failures.
- Android arch-friendly: The API is designed with the Android architecture components in mind, making integration into your apps easy.
Consider a use case where we want to construct the following pipeline:
- Wait for a UI signal to start the pipeline (say, button click)
- Ensure that there is internet connectivity
- Download an image from the given URL
- Rotate the downloaded image by 90 degrees
- Scale the image to a 400px x 400px size
- Overdraw the scaled image on top if its sibling
Pipe uses a Kotlin DSL to declare pipeline schematics. We can express the above pipeline as:
data classImagePipelineMember(valurl:String? =null,valimage:Bitmap? =null)valJOBS_REPO=InMemoryRepository<Job<ImagePipelineMember>>()valLOGGER=AndroidLogger("Pipe")funmakePipeline()= buildPipeline<ImagePipelineMember> { setRepository(JOBS_REPO) setLogger(LOGGER) addManualBarrier("start_barrier") addManualBarrier("internet_barrier") addStep("download", attempts=4) {ImagePipelineMember(image= downloadImage(it.url!!)) } addStep("rotate") {ImagePipelineMember(image= rotateBitmap(it.image!!,90.0f)) } addStep("scale") {ImagePipelineMember(image= scale(it.image!!,400,400)) } addCountedBarrier("overdraw", capacity=Int.MAX_VALUE) { allMembers-> allMembers.mapIndexed { index, member->val siblingIndex=if (index==0) allMembers.lastIndexelse index-1val resultingImage= overdraw(member.image!!, allMembers[siblingIndex].image!!)ImagePipelineMember(image= resultingImage) } }}
We can then use this factory function to create an instance of the pipeline:
val pipeline= makePipeline()
And then schedule jobs into it:
constvalJOB_TAG="IMAGE_TRANSFORM_JOBS"fun Pipeline<ImagePipelineMember>.createImageJobs(imageUrls:List<String>):List<Job<ImagePipelineMember>> { countedBarriers.forEach { it.setCapacity(imageUrls.size) }return imageUrls.map { url-> push(ImagePipelineMember(url= url), tag=JOB_TAG) }}
We can subscribe to these jobs' state changes in our activities/fragments viaLiveData:
val jobs= pipeline.createImageJobs(urls)jobs.forEach { job-> job.state.observe(this,Observer {// Update UI in response to state changes })}
See thestate machine for the details.
We can also fetch any ongoing jobs from the repository (e.g., if the fragment is re-created):
JOBS_REPO[JOB_TAG].forEach { (job, _, _)->// Perform actions on the jobs, such as interrupting them, unsubscribing from them, etc.}
To lift theinternet_barrier automatically when we have internet connectivity, we can use one of theBarrierExtensions:
pipeline.manualBarriers[1].liftWhenHasInternet(App.INSTANCE)
And finally, we can start the pipeline when a UI button is clicked:
someButton.setOnClickListener { pipeline.manualBarriers[0].lift()}The progress of a job is encoded via a state machine:
To see a full Android app example using the above pipeline, see thesample app. Or see the javadocshere.
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