Opening and closing objects

This information provides an insight into opening and closing IBM MQ objects.

To perform any of the following operations, we must first open the relevant IBM MQ object:

• Put messages on a queue
• Get (browse or retrieve) messages from a queue
• Set the attributes of an object
• Inquire about the attributes of any object

Use the MQOPEN call to open the object, using the options of the call to specify what we want to do with the object. The only exception is if we want to put a single message on a queue, then close the queue immediately. In this case, we can bypass the opening stage by using the MQPUT1 call (see Put one message on a queue using the MQPUT1 call ).

Before you open an object using the MQOPEN call, we must connect your program to a queue manager. This is explained in detail, for all environments, in Connect to and disconnecting from a queue manager.

There are four types of IBM MQ object that we can open:

• Queue
• Namelist
• Process definition
• Queue manager

You open all these objects in a similar way using the MQOPEN call. For more information about IBM MQ objects, see Object types.

We can open the same object more than once, and each time you get a new object handle. We might want to browse messages on a queue using one handle, and remove messages from the same queue using another handle. This saves using up resources to close and reopen the same object. We can also open a queue for browsing and removing messages at the same time.

Moreover, we can open multiple objects with a single MQOPEN and close them using MQCLOSE. See Distribution lists for information about how to do this.

When you attempt to open an object, the queue manager checks that we are authorized to open that object for the options that you specify in the MQOPEN call.

Objects are closed automatically when a program disconnects from the queue manager. In the IMS environment, disconnection is forced when a program starts processing for a new user following a GU (get unique) IMS call. On the IBM i platform, objects are closed automatically when a job ends.

It is good programming practice to close objects you have opened. Use the MQCLOSE call to do this.

Use the following links to find out more about opening and closing objects:

• Opening objects using the MQOPEN call
• Create dynamic queues
• Opening remote queues
• Closing objects using the MQCLOSE call

• Opening objects using the MQOPEN call
  Use this information to learn about opening objects using the MQOPEN call.
• Create dynamic queues
  Use a dynamic queue when we do not need the queue after the application ends.
• Opening remote queues
  A remote queue is a queue that is owned by a queue manager other than the one to which the application is connected.
• Closing objects using the MQCLOSE call
  To close an object, use the MQCLOSE call.

Parent topic: Writing a procedural application for queuing

Related concepts

• The Message Queue Interface overview
• Connect to and disconnecting from a queue manager
• Put messages on a queue
• Getting messages from a queue
• Inquiring about and setting object attributes
• Committing and backing out units of work
• Starting IBM MQ applications using triggers
• Work with the MQI and clusters
• Use and writing applications on IBM MQ for z/OS
• IMS and IMS bridge applications on IBM MQ for z/OS