table.cc

nachos下线程与同步的实验

#include "Table.h"

Table::Table(int size)
// create a table to hold at most 'size' entries.
{
     S = size;
     lock = new Lock("Tablelock");
     L = new int[size];
     value = new int[size];
     for ( int i=0; i<size; i++ )
         value[i] = 0;           
}

Table::~Table() //析构函数 
{
     for ( int i=0; i<=S; i++ ){
         Release(i);
     delete lock;
     delete value;
}

int 
Table::Alloc(void *object)
// allocate a table slot for 'object'.
// return the table index for the slot or -1 on error.
{
      int i;
      lock->Acquire();
      for ( i=0; i<S; i++ )
          if ( value[i] == 0 )
          {
               value[i] = 1;
               object = (void *)(L+i);
               break;
          }
      lock->Release();
      if ( i<S )
           return i+1;
      else 
           return -1;
}

void *Table::Get(int *index)
// return the object from table index 'index' or NULL on error.
// (assert index is in range).  Leave the table entry allocated
// and the pointer in place.
{
     if ( index>0 && index<=S )
          return (void *)(L+index-1);
     else
          return NULL;
}

void Table::Release(int index)  // free a table slot
{
     lokc->Acquire();
     if ( index>0 && index<=S )
          delete (L+index-1);
     lock->Release();
}