GDSX (Extended General Device Support) Manual

Design and Development

Extended General Device Support (GDSX) Manual—529931-001

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Example

This example shows how TSCODE handles a linked list of IOCBs associated with a

task (a TCB). Each item in this list uses two doublewords.

! initialize tcb queue header

CALL INIT^XLIST (tcb.qh);

! As a result, the header points to itself.

! The following gives possible content.

! Address Content

! tcb.qh 588362 588362

! tcb.qt 588366 588362

! put iocb onto tcb queue

CALL INSERT^XITEM (tcb.qt, @iocb );

! As a result, the iocb is linked to the header.

! The following gives possible content.

! Address Content

! tcb.qh 588362 589000

! tcb.qt 588366 589000

! iocb.tcblink[0] 589000 588362

! iocb.tcblink[1] 589004 588362

! take iocb off tcb queue

CALL DELETE^XITEM (@iocb );

! As a result, the iocb is removed from the list.

! Address Content

! tcb.qh 588362 588362

! tcb.qt 588366 588362

! iocb.tcblink[0] 589000 0

! iocb.tcblink[1] 589004 588362

Semaphore Control

The purpose of a semaphore is to ensure the serial access of a shared resource. A

task is considered to have acquired a resource when it owns the semaphore

associated with the resource. TSCODE defines and maintains a checkpoint

semaphore to guarantee that no more than one task is doing a checkpoint at any given

time. A unique user-defined semaphore should be established for each resource

requiring exclusive access. For example, a semaphore may be used to control access

to a global variable updated by several tasks. Three utility procedures are available for

managing semaphores other than the checkpoint semaphore: INIT^SEM, PSEM, and

VSEM. (The checkpoint semaphore is defined by TSCODE and managed with the

GET^CPSEM and GIVE^CPSEM procedures.)