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81 lines
1.5 KiB
Go
81 lines
1.5 KiB
Go
package collection
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import "sync"
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const queueGrowThreshold = 256
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// A Queue is a FIFO queue.
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type Queue struct {
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lock sync.Mutex
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elements []any
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head int
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tail int
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count int
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}
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// NewQueue returns a Queue object.
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func NewQueue(size int) *Queue {
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if size < 1 {
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panic("size must be greater than 0")
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}
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return &Queue{
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elements: make([]any, size),
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}
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}
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// Empty checks if q is empty.
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func (q *Queue) Empty() bool {
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q.lock.Lock()
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empty := q.count == 0
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q.lock.Unlock()
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return empty
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}
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// Put puts element into q at the last position.
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func (q *Queue) Put(element any) {
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q.lock.Lock()
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defer q.lock.Unlock()
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if q.count == len(q.elements) {
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nodes := make([]any, nextQueueCapacity(len(q.elements)))
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n := copy(nodes, q.elements[q.head:])
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copy(nodes[n:], q.elements[:q.head])
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q.head = 0
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q.tail = q.count
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q.elements = nodes
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}
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q.elements[q.tail] = element
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q.tail = (q.tail + 1) % len(q.elements)
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q.count++
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}
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// Take takes the first element out of q if not empty.
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func (q *Queue) Take() (any, bool) {
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q.lock.Lock()
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defer q.lock.Unlock()
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if q.count == 0 {
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return nil, false
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}
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element := q.elements[q.head]
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q.elements[q.head] = nil
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q.head = (q.head + 1) % len(q.elements)
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q.count--
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return element, true
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}
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func nextQueueCapacity(capacity int) int {
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if capacity < queueGrowThreshold {
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return capacity << 1
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}
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// Use a growth curve similar to Go slices: double small queues, then
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// transition smoothly toward 1.25x growth for larger queues.
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return capacity + ((capacity + 3*queueGrowThreshold) >> 2)
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}
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