z/OS HCD User's Guide
Previous topic | Next topic | Contents | Index | Contact z/OS | Library | PDF

Multi-user access

z/OS HCD User's Guide

Multi-user access

Up to z/OS V1R9 HCD, multiple users could read an IODF simultaneously, but no user could read an IODF while it was accessed in update mode by another user. Also, a user could only update an IODF, if no other user accessed the IODF, neither in read nor update mode.

Starting with release z/OS V1R10 HCD, when creating an IODF, you can specify a multi-user access option in the Create Work I/O Definition File dialog (Figure 13). The default is single-user access.

Having exclusive access to an IODF, users can also switch between single-user mode and multi-user access using an option in the Change I/O Definition File Attributes dialog.

  1. To enable an IODF for multi-user access you need ALTER access authority.
  2. You can check whether the multi-user access property is enabled for an IODF using View I/O definition file information from the Maintain I/O Definition Files task.

With the multi-user access option specified, an IODF is kept in exclusive update mode for a user only for the duration of a single transaction. If the updates of this transaction are committed, another user may update the IODF without requiring the first user to release it.

If a user is updating a multi-user access enabled IODF, HCD implements the following processing: HCD locks the IODF. If multiple subsequent users now also want to apply concurrent updates to the same IODF, they must wait in a queue. However, since the first user’s single transaction may last a split-second only, HCD repeats all other users’ subsequent update requests a couple of times. If all attempts fail, for example, because the first user updates the IODF using the dialog and is delaying required input, HCD will notify all other requesting users with a message, telling who is currently updating the IODF.

Associated change log files inherit the multi-user access ability from the IODFs.


When several users simultaneously work on the same IODF, exploiting the multi-user access capability, it is recommended that they co-ordinate their activities in order to ensure the consistency and integrity of the changes made to the IODF.

How to release a lock after an abnormal termination: In most cases of abnormal termination while working with IODFs in multi-user access, HCD invokes a recovery routine that deletes a pending lock. If, however, HCD cannot enter this routine, the lock remains active, and any user, when trying to access the IODF next time, receives a message about who is holding the lock.

In such a case, a user with ALTER access right must re-access the IODF exclusively and select action Change I/O definition file attributes to set back the multi-user access capability to NO. This action deletes the lock, and multi-user access can now be reactivated for that IODF.

Go to the previous page Go to the next page

Copyright IBM Corporation 1990, 2014