Learn the use of Java locks with Netty

java basic tutorialThe column introduces how to learn Java lock with Netty

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1 Lock objects and scope

Reduce the granularity
• 
  
  

2 The size of the lock object itself

Reduce space occupation
• 
  Atomic long V.S long
  The former is an object, including an object header to save hashcode, lock and other information. It occupies 16 bytes under a 64-bit system. Under a 64-bit system:
  
volatile long= 8 bytes
• AtomicLong = 8 bytes (volatile long) 16bytes (object header) 8 bytes (reference) = 32 bytes
• Save at least 24 bytes!
  

So Atomic* objects =》 Volatile primary type Static Atomic*FieldUpdater

3 Lock speed

Improve concurrency

LongCounter

Used for functions such as recording the number of bytes of memory allocation.

Under high concurrency: java.util.concurrent.atomic.AtomicLong => java.util.concurrent.atomic.LongAdder

Conclusion: Measure and use the latest JDK features in a timely manner

According to different situations, choose different concurrent package implementations

JDK< 1.8 Consider ConcurrentHashMapV8 (the version of ConcurrentHashMap in jDK8)

4 Choose different concurrency classes for different scenarios

Change according to needs

• Close and wait for the shutdown event executor (Event Executor) ：

  Object.wait/ notify =》 CountDownLatch
  
  

• Queue responsible for storing tasks in the Nio Event loop

  Jdk's LinkedBlockingQueue (MPMC, multi-producer Multiple consumers) -> jctools' MPSC
  io.netty.util.internal.PlatformDependent.Mpsc#newMpscQueue(int):
  
  
  

  5 The value of lock

  If you can’t use it, don’t use it

  In Netty application scenarios: partial serial and overall parallel>--one queue and multiple threads mode:
  Reduce the difficulty of user development, simplify logic, and improve processing performance
  Avoid the additional overhead of context switching and concurrency protection caused by locks
  

  Avoid using locks: Use ThreadLocal to avoid resource contention, such as Netty lightweight Level thread pool implementation

  
  

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