# MX\_GETQUEUE

> [HTML Version](mx_getqueue.htm)

_Rewritten April 2024_

**xcall MIAMEX, MX\_GETQUEUE, blkno, qblock**

MX\_GETQUEUE (MIAMEX 30) reads queue blocks from the system queue file (qflock.sys).

**Parameters**

_blkno_  ([Unsigned Int](integer-unsigned.htm.md))  \[in\]

Block (record) number to read.

_qblock_  ([Struture](structure.htm.md))  \[out\]

Structure to receive the block. The two structure definitionsm, ST\_QHEADER for the control record and ST\_QBLOCK for the other blocks, are defined in the file [ashinc:qflock.sdf](https://bitbucket.org/microsabio/soslib/src/master/907016/qflock.sdf) as follows:

defstruct ST\_QHEADER              \! Queue header block

   map2 QFREE,b,2            \! Free queue pointer

   map2 QUSED,b,2            \! Used queue pointer

   map2 Q'HIGHWATER,b,2      \! Highest used record #

   map2 LOG'COUNT'NOMORE,b,2 \! Logical users (instances) count \[13\]

   map2 Q'VERSION,s,4        \! version

   map2 Q'TOTOPS,i,4         \! total q adds \& deletes

   map2 Q'TOTREADS,i,4       \! total q adds \& deletes

   map2 Q'TOTWRITES,i,4      \! total q adds \& deletes

   map2 DUMMY1,x,16          \! Dummy filler was 24 \[13\] was 28 \[34\] was 24

endstruct



defstruct ST\_QBLOCK         \! qflock record

   map2 QNEXT,b,2          \! Pointer to next queue block

   map2 QTYPE,b,2          \! Queue block id type

   map2 QOWNER,b,2         \! Owner of queue block

   map2 QJUNK,b,2          \! (get back to 4x alignment)

   map2 QDATA              \! 32 bytes of data  (was 34)

   map2 QD'FLOCK,@QDATA    \! Format of FLOCK record

      map3 ACTION,b,2     \! Action

      map3 MODE,b,2       \! Mode

      map3 RECORD,b,4     \!  Record number

      map3 CHANNEL,b,4    \! Channel number \[12\] was 2

   map2 QD'IFLOCK,@QDATA   \! Format of inactive FLOCK record

   map2 QD'XLOCK,@QDATA    \! Format of XLOCK record

      map3 LOCK1,i,4      \! Primary lock code (INTEGER\!)

      map3 LOCK2,i,4      \! Secondard lock code (INTEGER\!)

      map3 LOCK3,b,2      \! New lock class (0=xlock,1=lock)

endstruct



The ST\_QBLOCK structure supports multiple layouts via overlays; the QTYPE field indicates which of the overlays to use, according to the following table:

| **Value** | **Queue block type** |
|------|------|
| 0 | Unused block |
| 3 | FLOCK – normal |
| 4 | XLOCK |
| 6 | FLOCK – inactive |
| 7 | ZLOCK (proprietary format) |
| 8 | RLOCK (proprietary format) |
| 9 | FLOCK – pending |


**Comments**

MX\_GETQUEUE is used primarily to track various kinds of inter-process locks or semaphores, in particular by the subroutines XLOCK and FLOCK.

The number of queue blocks is set by the QUEUE statement in miame.ini. 

Logically, the queue blocks are organized into two linked lists, one for the blocks that are in use (starting with the block number specified in the ST\_QHEADER.QUSED field), and the other (ST\_QHEADER.QFREE) for the available blocks. In either case, you can follow the linked list via the ST\_QBLOCK.QNEXT field.

Note that in a multi-user environment, the two linked lists may be actively updated. In order to traverse one of the lists safely, you should first lock the control via [MX\_QLOCK](mx_q_lock_unlok.htm.md) and unlock it when done using [MX\_QUNLOK](mx_q_lock_unlok.htm.md). 

**See Also**

•	QUTL.LIT (various interactive utility functions)

•	XLOCK[xs](keyword-types.htm.md) (general purpose locking API functions)

•	FLOCK[xs](keyword-types.htm.md) (file-specific locking API functions)