JDK

Study material

Clone on 19 Aug https://github.com/ymlai87416-oss/jdk https://github.com/ymlai87416-oss/cglib

https://github.com/kangjianwei/LearningJDK/blob/master/%E5%B7%B2%E9%98%85%E4%BB%A3%E7%A0%81%E6%B8%85%E5%8D%95_%E6%8C%89%E5%8A%9F%E8%83%BD%E6%8E%92%E5%BA%8F.md

Class loader

• How to load java class

Compile and JIT

• How JIT is being done?

Data structure

Java lib is java.util.*, and the code path is Link

1. ArrayList, LinkedLis:

   • The class Node is private, so it never return to outside. Link

2. HashSet, HashMap, ConcurrentHashMap

   • HashSet use HashMap to implement.
   • HashMap Internal parameter: load factor=0.75, max cap = 1024^3
   • HashMap if key list longer than 8, convert it to tree (Link)[https://github.com/openjdk/jdk/blob/4b03e135e157cb6cc9ba5eebf4a1f1b6e9143f48/src/java.base/share/classes/java/util/HashMap.java#L761]
   • before 1.7, it is front insert O(1), now it is back insert O(8), or O(log n)
   • ConcurrentHashMap use CAS to keep track of cell version and sychronized the rest.

3. TreeMap

4. Stack

5. PriorityQueue

   • A simple heap implements sift-up and sift-down

6. Queue and ArrayDeque

   • ArrayDeque is just a circular array

Concurrent

1. Thread: Link

   • locate at java.lang
   • Thread share the same classloader

2. CAS:

   • locate at java.util.concurrent.atomic
   • There is a variable U of Unsafe. A lot of native method there include compareAndSetInt()
   • Seems take times when there is a lot of state.
   • Implement spinning lock by CAS thread id to internal variable.

3. Reentrant lock:

   • Source code at java.util.concurrent.locks.ReentrantLock
   • Similiar to synchronized(lock)
   • have conditions so await = wait() and signal = notify() and signalAll = notifyAll()
   • Only 1 thread can enter the lock section

4. Semaphore

   • Source code at java.util.concurrent
   • AbstractQueueSynchronizer -> Sync -> FairSync and NonFairSync.
   • Leetcode question Dinning philosopher seems not working

5. Barrier

   • Source code at java.util.concurrent
   • Use to join a number of thread. Use spinning when wait.
   • Can also run some Runnable when it is tripped.

Garbage collector

• The garbage collector is locate at jdk.
• The garbage collector code is locate at Here
• Seems most of them have C1 and C2 folder (C1 for client and C2 for server)
• Need a long read

Code injection

cglib / aspectJ / byteBuddy