errproc.sample

mini database hpfile implement

/* 
 * This is a sample program to show you how to use the error protocol
 * In Minibase, each layer (e.g., the Buffer Manager) decides upon the
 * error conditions that it will check.  Each error is given an error code,
 * and all error codes for a layer are declared in an enumeration.
 * For the Buffer Manager, this enumeration is called bufErrCodes.
 * Next, each error code is associated with a string that is the 
 * corresponding error message.  For the Buffer Manager, this is done
 * in an array of strings called bufErrMsgs[], and the error code serves
 * as an index into this array.  This array is registered with Minibase
 * by creating a static "error_string_table" object.  These three steps
 * conclude the declaration of the errors to be checked for.  At run
 * time, the Buffer Manager code will check for occurrences of these errors, and
 * inform any caller by using the MINIBASE_FIRST_ERROR macro.
 * Further, if the Buffer Manager calls another layer, e.g., the DB layer, 
 * and the called layer reports an error, the Buffer Manager will pass this 
 * information on by making an entry in a global error queue, using
 * the MINIBASE_CHAIN_ERROR macro.  These points are illustrated in this
 * file through examples; for more details, read new_error.h or the Minibase
 * HTML page on errors.  There are additional methods available for
 * dealing with errors, but in this assignment, you will be be required to use them.
 */

///////////////////////////////////////////////////////////////////////////
//                                                                       //
// in buf.h file                                                         //
//                                                                       //
///////////////////////////////////////////////////////////////////////////

// Sample enums for internal errors; you need to add more.
enum bufErrCodes  {HASHTBLERROR, HASHNOTFOUND, BUFFEREXCEEDED};


///////////////////////////////////////////////////////////////////////////
//                                                                       //
// in buf.C                                                              //
//                                                                       //
///////////////////////////////////////////////////////////////////////////

// Define Buffer Manager error message 
static const char* bufErrMsgs[] = { "hash table error",
				    "hash entry not found",
				    "buffer pool full",
				    };

// Create a static "error_string_table" object, and register the error message 
// with the Minibase system
static error_string_table bufTable( BUFMGR, bufErrMsgs );

//
// Within each function, we check errors and push them into global queue
// e.g.

Status BufMgr::pinPage(PageId PageId_in_a_DB, Page*& page, int emptyPage)
{

 int Avail_Buframe;  // available buffer space, number of unpinned frames
 Status  st;	      // Stores the execution status

 .
 .
 .

 // Example error 1:   A page is requested, but the buffer pool is full. 
 if ( Avail_Buframe ==0 )
	// This error is detected for the first time, and so we use the 
	// MINIBASE_FIRST_ERROR macro to add it into global queue.
	return MINIBASE_FIRST_ERROR(BUFMGR,BUFFEREXCEEDED);

 .
 .
 .

 // Example error 2:  (Independent of the previous example.)  When the
 // Buffer Manager calls the DB layer to read a page, some error occurs
 // and is first detected by the DB layer.  Now, the Buffer Manager must
 // propagate information about this error.
 st = MINIBASE_DB->read_page(...);
 if (st != OK)
	// the error was detected in another layer, and so we use the 
	// MINIBASE_CHAIN_ERROR macro to add it to the global queue of errors
	return MINIBASE_CHAIN_ERROR(BUFMGR, st);

 .
 .
 .
 }