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A variation of the quantized bucket queue data structure, the calendar queue, has been applied to scheduling of discrete-event simulations, where the elements in the queue are future events prioritized by the time within the simulation that the events should happen. In this application, the ordering of events is critical, so the priorities ...
Such simulators require a good and efficient data structure as time spent on queue management can be significant. The calendar queue (with optimum bucket size) can approach O(1) average performance. Calendar queues are closely related to bucket queues but differ from them in how they are searched and in being dynamically resized.
The simulation must keep track of the current simulation time, in whatever measurement units are suitable for the system being modeled. In discrete-event simulations, as opposed to continuous simulations, time 'hops' because events are instantaneous – the clock skips to the next event start time as the simulation proceeds.
Queues are common in computer programs, where they are implemented as data structures coupled with access routines, as an abstract data structure or in object-oriented languages as classes. A queue has two ends, the top, which is the only position at which the push operation may occur, and the bottom, which is the only position at which the pop ...
A queue or queueing node can be thought of as nearly a black box. Jobs (also called customers or requests, depending on the field) arrive to the queue, possibly wait some time, take some time being processed, and then depart from the queue. A black box. Jobs arrive to, and depart from, the queue.
For instance, the bucket queue is a simple priority queue data structure consisting of an array indexed by priority, where each array cell contains a bucket of items with that priority. An extract-min operation performs a sequential search for the first non-empty bucket and chooses an arbitrary item in that bucket.
Representation of a FIFO queue with enqueue and dequeue operations. Depending on the application, a FIFO could be implemented as a hardware shift register, or using different memory structures, typically a circular buffer or a kind of list. For information on the abstract data structure, see Queue (data structure).
To improve performance, priority queues are typically based on a heap, giving O(log n) performance for inserts and removals, and O(n) to build the heap initially from a set of n elements. Variants of the basic heap data structure such as pairing heaps or Fibonacci heaps can provide better bounds for some operations. [1]