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Inside Macintosh: Files /

Chapter 2 - File Manager / Data Organization in Memory

The File I/O Queue

The file I/O queue is a standard Operating System queue (described in the chapter "Queue Utilities" in Inside Macintosh: Operating System Utilities) that contains parameter blocks for all asynchronous routines awaiting execution.

Each entry in the file I/O queue consists of a parameter block for the routine that was called. The File Manager uses the first four fields of each parameter block in processing the I/O requests in the queue.

TYPE ParamBlockRec =
RECORD
   qLink:         QElemPtr;      {next queue entry}
   qType:         Integer;       {queue type}
   ioTrap:        Integer;       {routine trap}
   ioCmdAddr:     Ptr;           {routine address}
                                 {rest of block}
END;

Field Description

qLink

A pointer to the next entry in the file I/O queue.

qType

The queue type. This field must always contain ORD(ioQType).

ioTrap

The trap word of the routine that was called.

ioCmdAddr

The address of the routine that was called.

You can get a pointer to the header of the file I/O queue by calling the File Manager utility function GetFSQHdr.

Assembly-Language Note

The global variable FSQHdr contains the header of the file I/O queue.