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Queue overflow results from trying to add an element onto a full queue and queue underflow happens when trying to remove an element from an empty queue. A bounded queue is a queue limited to a fixed number of items. [1] There are several efficient implementations of FIFO queues.
Circular buffering makes a good implementation strategy for a queue that has fixed maximum size. Should a maximum size be adopted for a queue, then a circular buffer is a completely ideal implementation; all queue operations are constant time. However, expanding a circular buffer requires shifting memory, which is comparatively costly.
Examples of FIFO status flags include: full, empty, almost full, and almost empty. A FIFO is empty when the read address register reaches the write address register. A FIFO is full when the write address register reaches the read address register. Read and write addresses are initially both at the first memory location and the FIFO queue is empty.
A double-ended queue can be used to store the browsing history: new websites are added to the end of the queue, while the oldest entries will be deleted when the history is too large. When a user asks to clear the browsing history for the past hour, the most recently added entries are removed.
A priority queue must at least support the following operations: is_empty: check whether the queue has no elements. insert_with_priority: add an element to the queue with an associated priority. pull_highest_priority_element: remove the element from the queue that has the highest priority, and return it.
For queue, because enqueuing and dequeuing occur at opposite ends, peek cannot be implemented in terms of basic operations, and thus is often implemented separately. One case in which peek is not trivial is in an ordered list type (i.e., elements accessible in order) implemented by a self-balancing binary search tree.
the producer must wait for the consumer to consume something if the queue is full. The semaphore solution to the producer–consumer problem tracks the state of the queue with two semaphores: emptyCount, the number of empty places in the queue, and fullCount, the number of elements in the queue.
In addition we assume that for each condition variable c, there is a queue c.q, which is a queue for threads waiting on condition variable c; All queues are typically guaranteed to be fair and, in some implementations, may be guaranteed to be first in first out. The implementation of each operation is as follows.