Deep Dive into Java Thread States and Synchronized Lock Implementation

This article provides an in-depth analysis of Java thread states and the internal implementation of the synchronized keyword.

It begins with the relationship between OS thread states and Java thread states, then dives into the synchronized lock mechanism, covering biased locking, lightweight locking, and heavyweight locking.

The explanation includes the role of the object header's Mark Word, the use of CAS operations, and the transition between lock states based on contention and epoch.

Example synchronized methods:

public synchronized void test1(){}

public void test2(){ synchronized(new Test()){}}

public static synchronized void test3(){}

Detailed bytecode-level analysis of monitorenter and monitorexit is presented, showing how locks are acquired, re-entered, released, and inflated. The article also discusses thread implementation models (kernel-level, user-level, hybrid) and the mapping of Java thread states to OS states, clarifying concepts like BLOCKED, WAITING, and TIMED_WAITING. Finally, it summarizes the lock upgrade process and provides notes on when each lock type is beneficial.