Android Architecture ( Synchronization and Scheduling )

Java Classes

• ReentrantLock
• A reentrant mutual exclusion lock that extends the built-in-monitor lock capabilities
• ReentrantReadWriteLock
• Improves performance when resources are read much more often than written
• Semaphore
• A non-negative integer that controls the access of multiple threads to a limited number of shared resources
• ConditionObject
• Block thread(s) until some condition(s) becomes true
• CountDownLatch
• Allows one or more threads to wait until a set of operations being performed in other threads complete

Considerations

• ReentrantLock have lower overhead than ReentrantReadWriteLock
• ReentrantReadWriteLock may enable more concurrency on multi-core or multi-processor hardware
• ConditionObject & Semaphore have higher overhead than ReentrantLock & ReentrantReadWriteLock
• ConditionObject & Semaphore are more expressive & more flexible
• ConditionObject can be used to lock a thread to keep other threads out of a critical section or keep in the critical section

ReentrantLock

Use mutual exclusion

Example: The bathroom in an airplane, only one person can use it at time

In Android implements the lock Interface and uses the Ganga four bridge pattern

Methods

• lock()
• lockInterruptibly()
• acquires the lock unless thread is interrupted
• unlock()

Readers-Witer Locks

• Is a synchonization mechanism often used in context with many concurrent threads
• Allow access to a shared resource
• Where multiple threads have read-only access OR
• one thread has write access
• Human Example 
• Formal Political debates: Many people listen the debate but only one person talk

RentrantReadWriteLock

• Use the Bridge pattern
• Inherits functionality from AbstractQueuedSynchronizer
• Implement fair or non-fair lock acquisition model
• Initialize the readerLock / writerLock data members
• Example: Using BluetoothSocket in the class BluetoothSocket.java
• Allows greater concurrency when accessing shared data than a ReentrantLock
• Used for scalable synchronization mechanism for parallel processing
• Tutorial