通過sychronized給對(duì)象加鎖，每個(gè)對(duì)象在實(shí)例化后，會(huì)同時(shí)實(shí)例出一個(gè)ObjectMoniter头朱，同時(shí)對(duì)象有對(duì)象頭（markOop
）座享，在對(duì)象頭中會(huì)存有當(dāng)前鎖狀態(tài)信息婉商，包含線程id似忧。
ObjectMoniter
objectMonitor.hpp

ObjectMonitor() {
    _header       = NULL;
    _count        = 0;
    _waiters      = 0,
    _recursions   = 0;
    _object       = NULL;
    _owner        = NULL;
    _WaitSet      = NULL;
    _WaitSetLock  = 0 ;
    _Responsible  = NULL ;
    _succ         = NULL ;
    _cxq          = NULL ;
    FreeNext      = NULL ;
    _EntryList    = NULL ;
    _SpinFreq     = 0 ;
    _SpinClock    = 0 ;
    OwnerIsThread = 0 ;
    _previous_owner_tid = 0;
  }

_count:當(dāng)有對(duì)象獲取鎖，count+1丈秩，對(duì)象釋放鎖count-1
_EntryList:當(dāng)有對(duì)象嘗試獲取鎖盯捌，加入entryList中
_WaitSet:當(dāng)調(diào)用wait方法，進(jìn)入等待隊(duì)列
_owner:擁有鎖當(dāng)線程蘑秽，當(dāng)鎖釋放是饺著，count-1同時(shí)owner置為NULL
當(dāng)使用sychronized給對(duì)象加鎖時(shí)，字節(jié)碼中是monitorenter給指定對(duì)象加鎖筷狼，給靜態(tài)方法加鎖時(shí)瓶籽，使用ACC_SYNCHRONIZED標(biāo)志給當(dāng)前對(duì)象加鎖。

public class SychronizedTest {

    private final Object lock = new Object();

    private volatile int count;

    public synchronized void method1() {
        count++;
    }

    public void method2() {
        synchronized (lock) {
            count++;
        }
    }
}

bytecode

public synchronized void method1();
    descriptor: ()V
    flags: ACC_PUBLIC, ACC_SYNCHRONIZED
    Code:
      stack=3, locals=1, args_size=1
         0: aload_0
         1: dup
         2: getfield      #4                  // Field count:I
         5: iconst_1
         6: iadd
         7: putfield      #4                  // Field count:I
        10: return
      LineNumberTable:
        line 14: 0
        line 15: 10
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      11     0  this   Lcom/chao/SychronizedTest;

public void method2();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=3, locals=3, args_size=1
         0: aload_0
         1: getfield      #3                  // Field lock:Ljava/lang/Object;
         4: dup
         5: astore_1
         6: monitorenter
         7: aload_0
         8: dup
         9: getfield      #4                  // Field count:I
        12: iconst_1
        13: iadd
        14: putfield      #4                  // Field count:I
        17: aload_1
        18: monitorexit
        19: goto          27
        22: astore_2
        23: aload_1
        24: monitorexit
        25: aload_2
        26: athrow
        27: return
      Exception table:
         from    to  target type
             7    19    22   any
            22    25    22   any
      LineNumberTable:
........