80 lines
1.7 KiB
Go
80 lines
1.7 KiB
Go
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package state
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import "encoding/binary"
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var (
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headKey = []byte("h")
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tailKey = []byte("t")
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dataKey = []byte("d")
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)
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// Queue allows us to fill up a range of the db, and grab from either end
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type Queue struct {
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store KVStore
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head uint64 // if Size() > 0, the first element is here
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tail uint64 // this is the first empty slot to Push() to
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}
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// NewQueue will load or initialize a queue in this state-space
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//
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// Generally, you will want to stack.PrefixStore() the space first
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func NewQueue(store KVStore) *Queue {
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q := &Queue{store: store}
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q.head = q.getCount(headKey)
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q.tail = q.getCount(tailKey)
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return q
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}
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// Tail returns the next slot that Push() will use
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func (q *Queue) Tail() uint64 {
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return q.tail
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}
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// Size returns how many elements are in the queue
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func (q *Queue) Size() uint64 {
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return q.tail - q.head
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}
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// Push adds an element to the tail of the queue and returns it's location
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func (q *Queue) Push(value []byte) uint64 {
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key := makeKey(q.tail)
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q.store.Set(key, value)
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q.tail++
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q.setCount(tailKey, q.tail)
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return q.tail - 1
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}
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// Pop gets an element from the end of the queue
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func (q *Queue) Pop() []byte {
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if q.Size() <= 0 {
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return nil
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}
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key := makeKey(q.head)
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value := q.store.Get(key)
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q.head++
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q.setCount(headKey, q.head)
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return value
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}
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func (q *Queue) setCount(key []byte, val uint64) {
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b := make([]byte, 8)
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binary.BigEndian.PutUint64(b, val)
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q.store.Set(key, b)
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}
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func (q *Queue) getCount(key []byte) (val uint64) {
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b := q.store.Get(key)
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if b != nil {
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val = binary.BigEndian.Uint64(b)
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}
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return val
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}
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// makeKey returns the key for a data point
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func makeKey(val uint64) []byte {
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b := make([]byte, 8+len(dataKey))
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copy(b, dataKey)
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binary.BigEndian.PutUint64(b[len(dataKey):], val)
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return b
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}
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