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Android Service Patterns
  AIDL Services Aren’t That Hard…
          Shree Kumar
          InnoMinds Software
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
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
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
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
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
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
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
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
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
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
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
Questions ?
   Shree Kumar
   shree.shree@gmail.com
http:://www.shreekumar.in/

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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/