A queue is a named, ordered list of elements that is used to pass information between threads of the same (related) process or between different (unrelated) processes.

Processes pass information to a queue in the form of elements. An element is a 32-bit unit of information. Queue elements can be values, flags, pointers to shared memory regions, anything that can fit into 32 bits. The format of a queue element depends entirely on the process that creates the queue (the queue owner). Only the queue owner can read elements from the queue; other processes can only write to the queue. Reading an element automatically removes it from the queue.

The process that creates the queue is known as the server process of the queue. The other processes that access the queue are known as client processes.

The owner of the queue (the server process) can choose the order in which to read incoming information and can examine queue elements without removing them from the queue. Queue elements can be added and accessed in First-In-First-Out (FIFO), Last-In-First-Out (LIFO), or priority-based order.

Any process that has the name of a queue can open the queue and write to it. The processes writing elements to the queue must use the format determined by the queue owner.

Queues are very efficient. They pass only 32-bit sized elements, rather than large data structures. However, queues can be used only for one-way communication, because a client process can write to a queue but cannot read from one.

Typically, processes use queues to transfer information about the contents of a shared memory. The elements in the queue could contain the address and length of data areas in shared memory objects. The sending process allocates a shared memory object and gives access to the shared memory to the queue owner. The sending process can free the shared memory after writing the elements to the queue because the shared memory will not be deallocated until the queue owner frees it.

Any thread in the process that owns the queue can examine queue elements without removing them. This is called peeking at the queue.

OS/2 supplies the process identifier of the process that writes an element to the queue, so that a process reading from or peeking at the queue can determine the origin of the element. The process identifier is returned as part of a REQUESTDATA data structure. Threads can use the ulData field of the REQUESTDATA data structure to pass additional information about the queue element.

If the queue is empty when a process attempts to read from it, the process can either wait for an element to become available or continue executing without reading from the queue. Semaphores can be used to indicate when an element is in the queue.