Android - user mode

contains
1.java layer
2.native layer - c,c++

under java
1.activities,services,receivers,providers

under native
1.daemons

communication between them
1.activities,services, .., and .. uses binder to communicate
2.a,s,.,. communicate with native layer using binders

but jni is also used in cases where the java can call on c,c++
also domain sockets can be used for communication

binder is a mechanism where a,s,r,p communicate with each other using ioctls and
binder driver

complication because, binder will invoke arbitraty threads from a pool to accomplish a task.In addition to arbitrary threads there is also main thread