synchronize原理

monitor锁

字节码指令

public class SynchronizedTest {
    static final Object lock = new Object();
    static int counter = 0;
    public static void main(String[] args) {
        synchronized (lock){
            counter++;
        }
        System.out.println(counter);
    }
}

  Last modified 2021-4-13; size 848 bytes
  MD5 checksum 524a368d98b2102c040f86818c154444
  Compiled from "SynchronizedTest.java"
public class org.example.concurrency.test.SynchronizedTest
  minor version: 0
  major version: 52
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Methodref          #6.#30         // java/lang/Object."<init>":()V
   #2 = Fieldref           #7.#31         // org/example/concurrency/test/SynchronizedTest.lock:Ljava/lang/Object;
   #3 = Fieldref           #7.#32         // org/example/concurrency/test/SynchronizedTest.counter:I
   #4 = Fieldref           #33.#34        // java/lang/System.out:Ljava/io/PrintStream;
   #5 = Methodref          #35.#36        // java/io/PrintStream.println:(I)V
   #6 = Class              #37            // java/lang/Object
   #7 = Class              #38            // org/example/concurrency/test/SynchronizedTest
   #8 = Utf8               lock
   #9 = Utf8               Ljava/lang/Object;
  #10 = Utf8               counter
  #11 = Utf8               I
  #12 = Utf8               <init>
  #13 = Utf8               ()V
  #14 = Utf8               Code
  #15 = Utf8               LineNumberTable
  #16 = Utf8               LocalVariableTable
  #17 = Utf8               this
  #18 = Utf8               Lorg/example/concurrency/test/SynchronizedTest;
  #19 = Utf8               main
  #20 = Utf8               ([Ljava/lang/String;)V
  #21 = Utf8               args
  #22 = Utf8               [Ljava/lang/String;
  #23 = Utf8               StackMapTable
  #24 = Class              #22            // "[Ljava/lang/String;"
  #25 = Class              #37            // java/lang/Object
  #26 = Class              #39            // java/lang/Throwable
  #27 = Utf8               <clinit>
  #28 = Utf8               SourceFile
  #29 = Utf8               SynchronizedTest.java
  #30 = NameAndType        #12:#13        // "<init>":()V
  #31 = NameAndType        #8:#9          // lock:Ljava/lang/Object;
  #32 = NameAndType        #10:#11        // counter:I
  #33 = Class              #40            // java/lang/System
  #34 = NameAndType        #41:#42        // out:Ljava/io/PrintStream;
  #35 = Class              #43            // java/io/PrintStream
  #36 = NameAndType        #44:#45        // println:(I)V
  #37 = Utf8               java/lang/Object
  #38 = Utf8               org/example/concurrency/test/SynchronizedTest
  #39 = Utf8               java/lang/Throwable
  #40 = Utf8               java/lang/System
  #41 = Utf8               out
  #42 = Utf8               Ljava/io/PrintStream;
  #43 = Utf8               java/io/PrintStream
  #44 = Utf8               println
  #45 = Utf8               (I)V
{
  static final java.lang.Object lock;
    descriptor: Ljava/lang/Object;
    flags: ACC_STATIC, ACC_FINAL
  static int counter;
    descriptor: I
    flags: ACC_STATIC
  public org.example.concurrency.test.SynchronizedTest();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial #1                  // Method java/lang/Object."<init>":()V
         4: return
      LineNumberTable:
        line 6: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0       5     0  this   Lorg/example/concurrency/test/SynchronizedTest;
  public static void main(java.lang.String[]);
    descriptor: ([Ljava/lang/String;)V
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=2, locals=3, args_size=1
         0: getstatic     #2                  // Field lock:Ljava/lang/Object;
         3: dup
         4: astore_1
         5: monitorenter
         6: getstatic     #3                  // Field counter:I
         9: iconst_1
        10: iadd
        11: putstatic     #3                  // Field counter:I
        14: aload_1
        15: monitorexit
        16: goto          24
        19: astore_2
        20: aload_1
        21: monitorexit
        22: aload_2
        23: athrow
        24: getstatic     #4                  // Field java/lang/System.out:Ljava/io/PrintStream;
        27: getstatic     #3                  // Field counter:I
        30: invokevirtual #5                  // Method java/io/PrintStream.println:(I)V
        33: return
      Exception table:
         from    to  target type
             6    16    19   any
            19    22    19   any
      LineNumberTable:
        line 11: 0
        line 12: 6
        line 13: 14
        line 14: 24
        line 15: 33
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      34     0  args   [Ljava/lang/String;
      StackMapTable: number_of_entries = 2
        frame_type = 255 /* full_frame */
          offset_delta = 19
          locals = [ class "[Ljava/lang/String;", class java/lang/Object ]
          stack = [ class java/lang/Throwable ]
        frame_type = 250 /* chop */
          offset_delta = 4
  static {};
    descriptor: ()V
    flags: ACC_STATIC
    Code:
      stack=2, locals=0, args_size=0
         0: new           #6                  // class java/lang/Object
         3: dup
         4: invokespecial #1                  // Method java/lang/Object."<init>":()V
         7: putstatic     #2                  // Field lock:Ljava/lang/Object;
        10: iconst_0
        11: putstatic     #3                  // Field counter:I
        14: return
      LineNumberTable:
        line 7: 0
        line 8: 10
}
SourceFile: "SynchronizedTest.java"