diff options
Diffstat (limited to 'vendor/github.com/allegro/bigcache/queue')
-rw-r--r-- | vendor/github.com/allegro/bigcache/queue/bytes_queue.go | 210 |
1 files changed, 210 insertions, 0 deletions
diff --git a/vendor/github.com/allegro/bigcache/queue/bytes_queue.go b/vendor/github.com/allegro/bigcache/queue/bytes_queue.go new file mode 100644 index 000000000..0285c72cd --- /dev/null +++ b/vendor/github.com/allegro/bigcache/queue/bytes_queue.go @@ -0,0 +1,210 @@ +package queue + +import ( + "encoding/binary" + "log" + "time" +) + +const ( + // Number of bytes used to keep information about entry size + headerEntrySize = 4 + // Bytes before left margin are not used. Zero index means element does not exist in queue, useful while reading slice from index + leftMarginIndex = 1 + // Minimum empty blob size in bytes. Empty blob fills space between tail and head in additional memory allocation. + // It keeps entries indexes unchanged + minimumEmptyBlobSize = 32 + headerEntrySize +) + +// BytesQueue is a non-thread safe queue type of fifo based on bytes array. +// For every push operation index of entry is returned. It can be used to read the entry later +type BytesQueue struct { + array []byte + capacity int + maxCapacity int + head int + tail int + count int + rightMargin int + headerBuffer []byte + verbose bool + initialCapacity int +} + +type queueError struct { + message string +} + +// NewBytesQueue initialize new bytes queue. +// Initial capacity is used in bytes array allocation +// When verbose flag is set then information about memory allocation are printed +func NewBytesQueue(initialCapacity int, maxCapacity int, verbose bool) *BytesQueue { + return &BytesQueue{ + array: make([]byte, initialCapacity), + capacity: initialCapacity, + maxCapacity: maxCapacity, + headerBuffer: make([]byte, headerEntrySize), + tail: leftMarginIndex, + head: leftMarginIndex, + rightMargin: leftMarginIndex, + verbose: verbose, + initialCapacity: initialCapacity, + } +} + +// Reset removes all entries from queue +func (q *BytesQueue) Reset() { + // Just reset indexes + q.tail = leftMarginIndex + q.head = leftMarginIndex + q.rightMargin = leftMarginIndex + q.count = 0 +} + +// Push copies entry at the end of queue and moves tail pointer. Allocates more space if needed. +// Returns index for pushed data or error if maximum size queue limit is reached. +func (q *BytesQueue) Push(data []byte) (int, error) { + dataLen := len(data) + + if q.availableSpaceAfterTail() < dataLen+headerEntrySize { + if q.availableSpaceBeforeHead() >= dataLen+headerEntrySize { + q.tail = leftMarginIndex + } else if q.capacity+headerEntrySize+dataLen >= q.maxCapacity && q.maxCapacity > 0 { + return -1, &queueError{"Full queue. Maximum size limit reached."} + } else { + q.allocateAdditionalMemory(dataLen + headerEntrySize) + } + } + + index := q.tail + + q.push(data, dataLen) + + return index, nil +} + +func (q *BytesQueue) allocateAdditionalMemory(minimum int) { + start := time.Now() + if q.capacity < minimum { + q.capacity += minimum + } + q.capacity = q.capacity * 2 + if q.capacity > q.maxCapacity && q.maxCapacity > 0 { + q.capacity = q.maxCapacity + } + + oldArray := q.array + q.array = make([]byte, q.capacity) + + if leftMarginIndex != q.rightMargin { + copy(q.array, oldArray[:q.rightMargin]) + + if q.tail < q.head { + emptyBlobLen := q.head - q.tail - headerEntrySize + q.push(make([]byte, emptyBlobLen), emptyBlobLen) + q.head = leftMarginIndex + q.tail = q.rightMargin + } + } + + if q.verbose { + log.Printf("Allocated new queue in %s; Capacity: %d \n", time.Since(start), q.capacity) + } +} + +func (q *BytesQueue) push(data []byte, len int) { + binary.LittleEndian.PutUint32(q.headerBuffer, uint32(len)) + q.copy(q.headerBuffer, headerEntrySize) + + q.copy(data, len) + + if q.tail > q.head { + q.rightMargin = q.tail + } + + q.count++ +} + +func (q *BytesQueue) copy(data []byte, len int) { + q.tail += copy(q.array[q.tail:], data[:len]) +} + +// Pop reads the oldest entry from queue and moves head pointer to the next one +func (q *BytesQueue) Pop() ([]byte, error) { + data, size, err := q.peek(q.head) + if err != nil { + return nil, err + } + + q.head += headerEntrySize + size + q.count-- + + if q.head == q.rightMargin { + q.head = leftMarginIndex + if q.tail == q.rightMargin { + q.tail = leftMarginIndex + } + q.rightMargin = q.tail + } + + return data, nil +} + +// Peek reads the oldest entry from list without moving head pointer +func (q *BytesQueue) Peek() ([]byte, error) { + data, _, err := q.peek(q.head) + return data, err +} + +// Get reads entry from index +func (q *BytesQueue) Get(index int) ([]byte, error) { + data, _, err := q.peek(index) + return data, err +} + +// Capacity returns number of allocated bytes for queue +func (q *BytesQueue) Capacity() int { + return q.capacity +} + +// Len returns number of entries kept in queue +func (q *BytesQueue) Len() int { + return q.count +} + +// Error returns error message +func (e *queueError) Error() string { + return e.message +} + +func (q *BytesQueue) peek(index int) ([]byte, int, error) { + + if q.count == 0 { + return nil, 0, &queueError{"Empty queue"} + } + + if index <= 0 { + return nil, 0, &queueError{"Index must be grater than zero. Invalid index."} + } + + if index+headerEntrySize >= len(q.array) { + return nil, 0, &queueError{"Index out of range"} + } + + blockSize := int(binary.LittleEndian.Uint32(q.array[index : index+headerEntrySize])) + return q.array[index+headerEntrySize : index+headerEntrySize+blockSize], blockSize, nil +} + +func (q *BytesQueue) availableSpaceAfterTail() int { + if q.tail >= q.head { + return q.capacity - q.tail + } + return q.head - q.tail - minimumEmptyBlobSize +} + +func (q *BytesQueue) availableSpaceBeforeHead() int { + if q.tail >= q.head { + return q.head - leftMarginIndex - minimumEmptyBlobSize + } + return q.head - q.tail - minimumEmptyBlobSize +} |