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Java Concurrency_V1 (Synchronized_Block (concept (reentrancy (Thread tries…

- - - - also called
        
        monitor locks
        
        intrinsic locks
        
        mutexes (mutual exclusion)
        
        only one thread can hold the lock
  - - - lock is on the object which is being invoked
      - spans the entire method body
  - - - thread will not be blocked when it tries to acquires a lock which it alreadys holds
    - - Thread tries to acquire a lock held by itself, the request succeeds
      - are acquired on per thread basis instead of invocation basis
      - Without reentrancy, when a subclass call a synchronized method of a super class, it could end up in a deadlock
    - - lock is automatically acquired by the executing thread before entering a synchronized block
      - automatically released when control exists the synchronized lock
    - - that one thread sees the effect of other thread in a predictable manner (memory visibility)
- - - - concept
        
        reads lower 32 bit written by thread A and higher 32 bit written by thread B when they are not synchronized
        
        JVM is permitted to read 64 bit read/ write as two separate 32 bit operations
      - impacted data types
        
        long
        
        double
  - - - completion
      - interruption
      - status flag
  - - - ensuring the visibility of their own state
      - that of the object they refer to
      - indicating an important lifecycle event has happened
    - - write to a variable do not depend on the current value
      - ensure only a single thread ever updates the values
      - variable does not participate in invariants with another variable
      - locking is not used for any other reason other than variable being accessed