Scheduler

In the previous sections a lot of concepts have been introduced. This section will cover one of the most important aspects of the framework: schedulers.

A scheduler is an object that schedules unit of work, and it's implemented throgh the the Scheduler type. This type allows to specify in which execution context the chain or part of the chain has to run. In particular, the developer can choose in which thread:

• an Observable has to run, with subscribeOn( )
• a Subscriber has to run, with observeOn( )

The framework already provide some schedulers:

• immediate( ), that executes work immediately on the current thread
• newThread( ), that creates a new Thread for each job
• computation( ), that can be used for event-loops, processing callbacks and other computational work
• io( ), that is intended for IO-bound work, based on an Executor thread-pool that will grow as needed
• ...

A really nice feature is the fact that applying the execution of a chain to a particular scheduler doesn't break the chain of operators, keeping the code clean and with a good level of declarativness.

An example of usage of schedulers is the following, in which an image is fetched from the network and then processed. A network request is a typical io-bound operation and it's performed in io() scheduler, while a processing operation is a cpu-bound operation and it's performed in a computation() scheduler.

myObservableServices.retrieveImage(url)
  .subscribeOn(Schedulers.io())
  .observeOn(Schedulers.computation())
  .subscribe(bitmap -> processImage(bitmap));