/// <summary>读取内存块，自动识别是否空闲</summary>
/// <param name="view"></param>
public Boolean Read(MemoryView view)
{
var p = Position;
if (p < 0)
{
throw new ArgumentNullException(nameof(Position));
}
if (p + 8 >= view.Capacity)
{
return(false);
}
// 不管是否空闲块，都是长度开头
var len = view.ReadInt64(p);
var flag = len & 0b0000_0111;
len -= flag;
Size = len;
Free = (flag & 0b0000_00001) > 0;
PrevFree = (flag & 0b0000_00010) > 0;
// 如果是空闲块，还要读取前后空闲指针，最后8字节则可以不用读取
if (Free)
{
Next = view.ReadInt64(p + 8);
}
else
{
Next = 0;
}
#if DEBUG
XTrace.WriteLine("Read " + this);
#endif
return(true);
}
/// <summary>写入内存块</summary>
/// <param name="view"></param>
public void Write(MemoryView view)
{
var p = Position;
if (p < 0)
{
throw new ArgumentNullException(nameof(Position));
}
#if DEBUG
//XTrace.WriteLine("Write " + this);
#endif
// 8字节对齐
var len = Align(Size);
var len2 = len;
if (Free)
{
len2 |= 0b0000_00001;
}
if (PrevFree)
{
len2 |= 0b0000_00010;
}
view.Write(p, len2);
// 空闲块有下一块指针，尾部也有长度标记
if (Free)
{
view.Write(p + 8, Next);
if (Next > 0)
{
view.Write(p + len - 8, len2);
}
// 修改下一个相邻块的PrevFree
p += len;
if (p + 8 < view.Capacity)
{
len = view.ReadInt64(p);
// 标记下一相邻块的PrevFree为1
if ((len & 0b0000_00010) == 0)
{
len |= 0b0000_00010;
view.Write(p, len);
}
}
}
}
