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semaphore.go
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semaphore.go
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package sync
import (
"fmt"
"sync"
"time"
sema "golang.org/x/sync/semaphore"
)
type prioritySemaphore struct {
name string
limit int
pending *priorityQueue
running map[string]bool
semaphore *sema.Weighted
lock *sync.Mutex
}
var _ Semaphore = &prioritySemaphore{}
func newSemaphore(name string, limit int) *prioritySemaphore {
return &prioritySemaphore{
name: name,
limit: limit,
pending: &priorityQueue{itemByKey: make(map[string]*item)},
semaphore: sema.NewWeighted(int64(limit)),
running: make(map[string]bool),
lock: &sync.Mutex{},
}
}
func (s *prioritySemaphore) getName() string {
return s.name
}
func (s *prioritySemaphore) getLimit() int {
return s.limit
}
func (s *prioritySemaphore) getCurrentPending() []string {
keys := []string{}
for _, item := range s.pending.items {
keys = append(keys, item.key)
}
return keys
}
func (s *prioritySemaphore) getCurrentRunning() []string {
keys := []string{}
for k := range s.running {
keys = append(keys, k)
}
return keys
}
func (s *prioritySemaphore) resize(n int) bool {
s.lock.Lock()
defer s.lock.Unlock()
cur := len(s.running)
// downward case, acquired n locks
if cur > n {
cur = n
}
semaphore := sema.NewWeighted(int64(n))
status := semaphore.TryAcquire(int64(cur))
if status {
s.semaphore = semaphore
s.limit = n
}
return status
}
func (s *prioritySemaphore) removeFromQueue(key string) {
s.lock.Lock()
defer s.lock.Unlock()
s.pending.remove(key)
}
func (s *prioritySemaphore) acquireLatest() string {
s.lock.Lock()
defer s.lock.Unlock()
if s.pending.Len() == 0 {
return ""
}
ready := s.pending.peek()
if s.semaphore.TryAcquire(1) {
_ = s.pending.pop()
s.running[ready.key] = true
return ready.key
}
return ""
}
func (s *prioritySemaphore) release(key string) bool {
s.lock.Lock()
defer s.lock.Unlock()
if _, ok := s.running[key]; ok {
delete(s.running, key)
// When semaphore resized downward
// Remove the excess holders from map once the done.
if len(s.running) >= s.limit {
return true
}
s.semaphore.Release(1)
}
return true
}
func (s *prioritySemaphore) addToQueue(key string, creationTime time.Time) bool {
s.lock.Lock()
defer s.lock.Unlock()
if _, ok := s.running[key]; ok {
return false
}
if s.pending.isPending(key) {
return false
}
s.pending.add(key, creationTime.UnixNano())
return true
}
func (s *prioritySemaphore) tryAcquire(key string) (bool, string) {
s.lock.Lock()
defer s.lock.Unlock()
if _, ok := s.running[key]; ok {
return true, ""
}
waitingMsg := fmt.Sprintf("Waiting for %s lock. Available queue status: %d/%d", s.name, s.limit-len(s.running), s.limit)
// Check whether requested key is in front of priority queue.
// If it is in front position, it will allow to acquire lock.
// If it is not a front key, it needs to wait for its turn.
var nextKey string
if s.pending.Len() > 0 {
item := s.pending.peek()
nextKey = fmt.Sprintf("%v", item.key)
if key != nextKey {
return false, waitingMsg
}
}
if s.acquire(nextKey) {
s.pending.pop()
return true, ""
}
return false, waitingMsg
}
func (s *prioritySemaphore) acquire(key string) bool {
if s.semaphore.TryAcquire(1) {
s.running[key] = true
return true
}
return false
}