hotspot中，标记字中各字段的位置

description.md

test.cpp用于打印出hotspot中，标记字中各个字段的位置和相关掩码的值，其中**_in_place是指将当前字段的掩码与该字段的便宜结合之后得到的值

在32位平台上，test.cpp打印如下结果：

age_bits = 4
lock_bits = 2
biased_lock_bits = 1
max_hash_bits = 25
hash_bits = 25
cms_bits = 0
epoch_bits = 2

lock_shift = 0
biased_lock_shift = 2
age_shift = 3
cms_shift = 7
hash_shift = 7
epoch_shift = 7

lock_mask = 3
lock_mask_in_place = 3
biased_lock_mask = 7
biased_lock_bit_in_place = 4
age_mask = 15
age_mask_in_place = 120
epoch_mask = 3
epoch_mask_in_place = 384
cms_mask = 0
cms_mask_in_place = 0
hash_mask = 33554431
hash_mask_in_place = -128

test.cpp

#include "stdio.h"


//from macros.hpp
#ifdef  _LP64
#define LP64_ONLY(code) code
#define NOT_LP64(code)
#else  // !_LP64
#define LP64_ONLY(code)
#define NOT_LP64(code) code
#endif // _LP64




//from globalDefinitions_gcc.hpp
typedef int                     intptr_t;
typedef unsigned int            uintptr_t;




//from globalDefinitions.hpp
typedef uintptr_t     address_word; // unsigned integer which will hold a pointer

#ifdef _LP64
const int LogBytesPerWord    = 3;
#else
const int LogBytesPerWord    = 2;
#endif
const int LogBitsPerByte     = 3;
const int LogBitsPerWord     = LogBitsPerByte + LogBytesPerWord;
const int BytesPerWord       = 1 << LogBytesPerWord;
const int BitsPerWord        = 1 << LogBitsPerWord;

const intptr_t OneBit     =  1; // only right_most bit set in a word

#define nth_bit(n)        (n >= BitsPerWord ? 0 : OneBit << (n))
#define right_n_bits(n)   (nth_bit(n) - 1)




//from markOop.hpp
enum {   age_bits                 = 4,
         lock_bits                = 2,
         biased_lock_bits         = 1,
         max_hash_bits            = BitsPerWord - age_bits - lock_bits - biased_lock_bits,
         hash_bits                = max_hash_bits > 31 ? 31 : max_hash_bits,
         cms_bits                 = LP64_ONLY(1) NOT_LP64(0),
         epoch_bits               = 2
  };

  // The biased locking code currently requires that the age bits be
  // contiguous to the lock bits.
  enum { lock_shift               = 0,
         biased_lock_shift        = lock_bits,
         age_shift                = lock_bits + biased_lock_bits,
         cms_shift                = age_shift + age_bits,
         hash_shift               = cms_shift + cms_bits,
         epoch_shift              = hash_shift
  };

  enum { lock_mask                = right_n_bits(lock_bits),
         lock_mask_in_place       = lock_mask << lock_shift,
         biased_lock_mask         = right_n_bits(lock_bits + biased_lock_bits),
         biased_lock_mask_in_place= biased_lock_mask << lock_shift,
         biased_lock_bit_in_place = 1 << biased_lock_shift,
         age_mask                 = right_n_bits(age_bits),
         age_mask_in_place        = age_mask << age_shift,
         epoch_mask               = right_n_bits(epoch_bits),
         epoch_mask_in_place      = epoch_mask << epoch_shift,
         cms_mask                 = right_n_bits(cms_bits),
         cms_mask_in_place        = cms_mask << cms_shift
#ifndef _WIN64
         ,hash_mask               = right_n_bits(hash_bits),
         hash_mask_in_place       = (address_word)hash_mask << hash_shift
#endif
  };

#ifdef _WIN64
    // These values are too big for Win64
    const static uintptr_t hash_mask = right_n_bits(hash_bits);
    const static uintptr_t hash_mask_in_place  =
                            (address_word)hash_mask << hash_shift;
#endif



//test
int main(int argc, char* argv[]) {
    printf("age_bits = %d\n", age_bits);
    printf("lock_bits = %d\n", lock_bits);
    printf("biased_lock_bits = %d\n", biased_lock_bits);
    printf("max_hash_bits = %d\n", max_hash_bits);
    printf("hash_bits = %d\n", hash_bits);
    printf("cms_bits = %d\n", cms_bits);
    printf("epoch_bits = %d\n", epoch_bits);
    printf("\n");
  
    printf("lock_shift = %d\n", lock_shift);
    printf("biased_lock_shift = %d\n", biased_lock_shift);
    printf("age_shift = %d\n", age_shift);
    printf("cms_shift = %d\n", cms_shift);
    printf("hash_shift = %d\n", hash_shift);
    printf("epoch_shift = %d\n", epoch_shift);
    printf("\n");
  
    printf("lock_mask = %d\n", lock_mask);
    printf("lock_mask_in_place = %d\n", lock_mask_in_place);
    printf("biased_lock_mask = %d\n", biased_lock_mask);
    printf("biased_lock_bit_in_place = %d\n", biased_lock_bit_in_place);
    printf("age_mask = %d\n", age_mask);
    printf("age_mask_in_place = %d\n", age_mask_in_place);
    printf("epoch_mask = %d\n", epoch_mask);
    printf("epoch_mask_in_place = %d\n", epoch_mask_in_place);
    printf("cms_mask = %d\n", cms_mask);
    printf("cms_mask_in_place = %d\n", cms_mask_in_place);
    printf("hash_mask = %d\n", hash_mask);
    printf("hash_mask_in_place = %d\n", hash_mask_in_place);
}