Android Service Patterns
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This document discusses common patterns for implementing Android services using AIDL for inter-process communication. It begins by introducing services and AIDL, then discusses the challenges of using AIDL across processes. It presents two common patterns - the "lock" pattern for exclusive access to shared resources, and a "broadcast" pattern for simultaneous access. The lock pattern implementation uses worker threads and locks to serialize access. The broadcast pattern maintains listener lists to share updates with multiple clients.
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Android Service Patterns
- 1. Android Service Patterns AIDL Services Aren’t That Hard… Shree Kumar InnoMinds Software
- 2. Motivation • Writing services is useful & fun – Not to mention, painful ! • Documentation is present, but… – Scattered – Deals mostly with mechanics • Can a 45 minute session make a difference ? Android Service Patterns | DroidCon India 2011
- 3. Objectives • Clarification on the term “Patterns” – NOT design patterns a-la Grady Booch! • This talk gives you – Quick overview of AIDL based Services – Features & Pains – Writing useful services as patterns Android Service Patterns | DroidCon India 2011
- 4. Intro to Android Services • The “Service” concept – Application component – Typically used for long-running operations – Does not automatically create • new processes or threads • Can be roughly classified based on – Interaction Mechanism : Started, Bound – Application Boundaries : In-process, IPC Android Service Patterns | DroidCon India 2011
- 5. AIDL based IPC Services • Android Interface Definition Language • Inter-Process Communication to – Expose interfaces to other applications • More complicated than “Messenger” Android Service Patterns | DroidCon India 2011
- 6. Why all the pain? • “natural” interactions with the service – Calls & callbacks – With complex objects as parameters • And all these across process boundaries! Android Service Patterns | DroidCon India 2011
- 7. Hello, AIDL Service! • Implements onBind() – Exposes interface by implementing stubs • Exports via AndroidManifest.xml • Client apps bind via Intents – Use interface methods – Callbacks require app to implement stubs corresponding to callback interface Android Service Patterns | DroidCon India 2011
- 8. What’s not-so-nice there ? • No control over binding – onBind() return value is cached! • No control over threading • Code messier than in-process interface – No support for exceptions – Dead remote object exceptions => messy code – Callbacks not invoked in UI context • No concept of versioning Android Service Patterns | DroidCon India 2011
- 9. Common Service Patterns • Exclusive access to shared resource – The “lock” pattern • Simultaneous access to shared resource – “serialize”, “broadcast” patterns • Less common – Service versioning – Multiple objects of the same type Android Service Patterns | DroidCon India 2011
- 10. The “lock” pattern • Exclusive access using “locks” – Take lock before use – Release lock after use • Looks simple ? – Multi-app access – Appropriate threading model – Improper app lock handling => starvation Android Service Patterns | DroidCon India 2011
- 11. Locked Service Implementation • Associate locks with calling process • Worker thread for serialization – Started on service creation – Producer-consumer modeling • Java.util.concurrent provides ample support • Partial solution for starvation – Evict clients on DeadObjectException Android Service Patterns | DroidCon India 2011
- 12. Shared Access Service • “broadcast” method – Shares a state update with multiple listeners – Broadcast receivers don’t make the cut • Can’t bind a Service inside them • Implementation – Reuse “listener” concept • Clients add/remove listeners – Service maintains list of listeners • Updates listeners when needed • Removes dead objects – Reference : MindTheRobot Android Architecture Tutorial Android Service Patterns | DroidCon India 2011
- 13. Questions ? Shree Kumar shree.shree@gmail.com http:://www.shreekumar.in/