Inter-process method invocation using Binder in Android.

1. Inter-process method invocation
in Android
2011.4.9
Tetsuyuki Kobayashi
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2. Who am I?
 20+ years involved in embedded systems
 10 years in real time OS, such as iTRON
 10 years in embedded Java Virtual Machine
 Now GCC, Linux, QEMU, Android, …
 Blogs
 http://d.hatena.ne.jp/embedded/ (Personal)
 http://blog.kmckk.com/ (Corporate)
 Twitter
 @tetsu_koba
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3. Today's topic
 inter process communications in
Android
 Inter process method invocation
using Binder
 AIDL
 Example of inter process
method invocation
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4. Inter Process Communication
Activity
Activity Window Alarm
Manager Manager Manager
Kernel
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5. Abstraction of Inter Process
Communication
More abstract
Intent
AIDL
Binder
No need to use Binder directly.
AIDL requires multi-thread programming
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In most case Intent is easy and powerful enough.

6. Invoking method via interface
caller
callee
In the same process
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7. Inter-process invocation
caller
interface
caller
interface
How?
callee
interface
callee
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8. Inter-process invocation
caller
interface
Proxy
caller
interface Binder in kernel
Binder Thread
callee
Stub
interface
callee
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9. android.os.Parcel
Delivering arguments of method
”flatten” ”unflatten”
transmit
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10. Describing in UML ...
<<interface>>
Proxy Stub
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11. Describing in UML ...
caller
<<interface>> calls
implements
Proxy Stub
extends
callee
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12. AIDL
Auto generated from .aidl file caller
<<interface>>
Proxy Stub
callee
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13. Use case: Who calls ”onPause”
in Activity?
2:Send message Activity
by Handler
3:”onPause”
is called
queue Looper in main
thread
Activity
Manager Main
Main
Binder Thread
Thread
Binder
Thread #1
Thread #1
Kernel
1:Call ”schedulePauseActivity”
across process
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14. Binder
 /etc/binder
 Not for general purpose. Tuned for specific
transaction.
 Multi-thread aware
 Have internal data per thead
 (CF. Socket have internal data per fd.)
 Not use ”write” and ”read”. Write and read at
once by ”ioctl”.
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15. Transaction of Binder
Process A and B have different memory space.
They can not see each other.
Kernel Process B
Process A
Binder
Copy memory by copy_from _user
Then, wake up process B
Kernel
Process B
Binder
Process A
Copy memory by copy_to_user
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16. See also
rd

3 session of Yokohama Android Platform club
 http://www.yokohama.android-pf.org/study/dai-san-kai-benkyou-kai

1st session of Android SDK work group
 http://www.android-group.jp/index.php?%CA%D9%B6%AF%B2%F1%2FAndr
 KMC blog
 http://blog.kmckk.com/archives/3611344.html
 http://blog.kmckk.com/archives/3613707.html
 http://blog.kmckk.com/archives/3627888.html
 http://blog.kmckk.com/archives/3645070.html
 http://blog.kmckk.com/archives/3647635.html
 http://blog.kmckk.com/archives/3617229.html
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17. Q&A
Thank you for listening!
Any comments to blogs are welcome.
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