认识Java中的Stub与StubQueue

static StubQueue* _code;

// InterpreterCodeSize是在平台相关
// 的templateInterpreter_x86.hpp中
// 定义的，64位下是256 * 1024
int code_size = InterpreterCodeSize;
_code = new StubQueue(
                new InterpreterCodeletInterface, 
                code_size, 
                NULL,
                "Interpreter");

class Stub VALUE_OBJ_CLASS_SPEC { ... };

class InterpreterCodelet: public Stub {
 private:
  int                _size;         // the size in bytes
  const char*        _description;  // a description of the codelet, for debugging & printing
  Bytecodes::Code    _bytecode;     // associated bytecode if any
 
 public:
  // Code info
  address code_begin() const  {
     return (address)this + round_to(sizeof(InterpreterCodelet), CodeEntryAlignment);
  }
  address code_end() const {
     return (address)this + size();
  }
 
  int size() const {
     return _size;
  }
  // ...
  int code_size() const { 
     return code_end() - code_begin();  
  }
  // ...
};

class StubQueue: public CHeapObj<mtCode> {
 private:
  StubInterface* _stub_interface;     // the interface prototype
  address        _stub_buffer;        // where all stubs are stored
 
  int            _buffer_size;       // the buffer size in bytes
  int            _buffer_limit;      // the (byte) index of the actual buffer limit (_buffer_limit <= _buffer_size)
 
  int            _queue_begin;       // the (byte) index of the first queue entry (Word-aligned)
  int            _queue_end;         // the (byte) index of the first entry after the queue (word-aligned)
 
  int            _number_of_stubs;   // the number of buffered stubs
 
 
  bool is_contiguous() const {
      return _queue_begin <= _queue_end;
  }
  int index_of(Stub* s) const {
      int i = (address)s - _stub_buffer;
      return i;
  }
  Stub* stub_at(int i) const {
      return (Stub*)(_stub_buffer + i);
  }
  Stub* current_stub() const {
      return stub_at(_queue_end);
  }
 
  // ...
}

StubQueue::StubQueue(
 StubInterface* stub_interface,  // InterpreterCodeletInterface对象
 int            buffer_size,     // 256*1024
 Mutex*         lock,
 const char*    name) : _mutex(lock)
{
  intptr_t     size = round_to(buffer_size, 2*BytesPerWord); // BytesPerWord的值为8
  BufferBlob*  blob = BufferBlob::create(name, size); // 在StubQueue中创建BufferBlob对象
 
  _stub_interface  = stub_interface;
 
  _buffer_size     = blob->content_size();
  _buffer_limit    = blob->content_size();
  _stub_buffer     = blob->content_begin();
 
  _queue_begin     = 0;
  _queue_end       = 0;
  _number_of_stubs = 0;
}

BufferBlob* BufferBlob::create(const char* name, int buffer_size) {
  // ...
  BufferBlob*    blob = NULL;
  unsigned int   size = sizeof(BufferBlob);
 
  // align the size to CodeEntryAlignment
  size = align_code_offset(size);
  size += round_to(buffer_size, oopSize); // oopSize是一个指针的宽度，在64位上就是8
 
  {
     MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
     blob = new (size) BufferBlob(name, size);
  }
 
  return blob;
}

void* BufferBlob::operator new(size_t s, unsigned size, bool is_critical) throw() {
  void* p = CodeCache::allocate(size, is_critical);
  return p;
}