関小君刷题记

0x00:  b2 00 02         getstatic  Java .lang.System.out0x03:  12 03            ldc "Hello， World!"0x05:  b6 00 04         invokevirtual  Java .io.PrintStream.println0x08:  b1               return

0x00:  55                    push   rbp0x01:  48 89 e5              mov    rbp，rsp0x04:  48 83 ec 10           sub    rsp，0x100x08:  48 8d 3d 3b 00 00 00  lea    rdi，[rip+0x3b]                                    ; 加载 "Hello， World!\n"0x0f:  c7 45 fc 00 00 00 00  mov    DWORD PTR [rbp-0x4]，0x00x16:  b0 00                 mov    al，0x00x18:  e8 0d 00 00 00        call   0x12                                    ; 调用 printf 方法0x1d:  31 c9                 xor    ecx，ecx0x1f:  89 45 f8              mov    DWORD PTR [rbp-0x8]，eax0x22:  89 c8                 mov    eax，ecx0x24:  48 83 c4 10           add    rsp，0x100x28:  5d                    pop    rbp0x29:  c3                    ret

    private void init(final String fileName， final int fileSize) throws IOException {        this.fileName = fileName;        this.fileSize = fileSize;        this.file = new File(fileName);        this.fileFromOffset = Long.parseLong(this.file.getName());        boolean ok = false;
        ensureDirOK(this.file.getParent());
        try {            this.fileChannel = new RandomAccessFile(this.file， "rw").getChannel();            this.mappedByteBuffer = this.fileChannel.map(MapMode.READ_WRITE， 0， fileSize);            TOTAL_MAPPED_VIRTUAL_MEMORY.addAndGet(fileSize);            TOTAL_MAPPED_FILES.incrementAndGet();            ok = true;        } catch (FileNotFoundException e) {            log.error("create file channel " + this.fileName + " Failed. "， e);            throw e;        } catch (IOException e) {            log.error("map file " + this.fileName + " Failed. "， e);            throw e;        } finally {            if (!ok && this.fileChannel != null) {                this.fileChannel.close();            }        }    }

//文件预热，OS_PAGE_SIZE = 4kb 相当于每 4kb 就写一个 byte 0 ，将所有的页都加载到内存，真正使用的时候就不会发生缺页异常了 public void warmMappedFile(FlushDiskType type， int pages) {        long beginTime = System.currentTimeMillis();        ByteBuffer byteBuffer = this.mappedByteBuffer.slice();        int flush = 0;        long time = System.currentTimeMillis();        for (int i = 0， j = 0; i < this.fileSize; i += MappedFile.OS_PAGE_SIZE， j++) {            byteBuffer.put(i， (byte) 0);            // force flush when flush disk type is sync            if (type == FlushDiskType.SYNC_FLUSH) {                if ((i / OS_PAGE_SIZE) - (flush / OS_PAGE_SIZE) >= pages) {                    flush = i;                    mappedByteBuffer.force();                }            }
            // prevent gc            if (j % 1000 == 0) {                log.info("j={}， costTime={}"， j， System.currentTimeMillis() - time);                time = System.currentTimeMillis();                try {                // 这里sleep(0)，让线程让出 CPU 权限，供其他更高优先级的线程执行，此线程从运行中转换为就绪                    Thread.sleep(0);                } catch (InterruptedException e) {                    log.error("Interrupted"， e);                }            }        }
        // force flush when prepare load finished        if (type == FlushDiskType.SYNC_FLUSH) {            log.info("mapped file warm-up done， force to disk， mappedFile={}， costTime={}"，                this.getFileName()， System.currentTimeMillis() - beginTime);            mappedByteBuffer.force();        }        log.info("mapped file warm-up done. mappedFile={}， costTime={}"， this.getFileName()，            System.currentTimeMillis() - beginTime);
        this.mlock();    }

 Field 对象的 getInt方法  先安全检查 ，然后调用 FieldAccessor    @CallerSensitive    public int getInt(Object obj)        throws IllegalArgumentException， IllegalAccessException    {        if (!override) {            if (!Reflection.quickCheckMemberAccess(clazz， modifiers)) {                Class<?> caller = Reflection.getCallerClass();                checkAccess(caller， clazz， obj， modifiers);            }        }        return getFieldAccessor(obj).getInt(obj);    }

 获取field在所在对象中的地址的偏移量 fieldoffset    UnsafeFieldAccessorImpl(Field var1) {            this.field = var1;            if(Modifier.isStatic(var1.getModifiers())) {                this.fieldOffset = unsafe.staticFieldOffset(var1);            } else {                this.fieldOffset = unsafe.objectFieldOffset(var1);            }
            this.isFinal = Modifier.isFinal(var1.getModifiers());     }

 UnsafeStaticIntegerFieldAccessorImpl 调用unsafe中的方法     public int getInt(Object var1) throws IllegalArgumentException {          return unsafe.getInt(this.base， this.fieldOffset);     }

jdk6  --- 32 位系统下    public final static class VolatileLong{        public volatile long value = 0L;        public long p1， p2， p3， p4， p5， p6; // 填充字段    }
jdk7 通过继承
   public class VolatileLongPadding {       public volatile long p1， p2， p3， p4， p5， p6; // 填充字段   }   public class VolatileLong extends VolatileLongPadding {       public volatile long value = 0L;   }
jdk8 通过注解
   @Contended   public class VolatileLong {       public volatile long value = 0L;   }