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vendor/go.mongodb.org/mongo-driver/x/mongo/driver/session/session_pool.go:17


// Node represents a server session in a linked list
type Node struct {
   *Server
   next *Node
   prev *Node
}

// Pool is a pool of server sessions that can be reused.
type Pool struct {
   descChan <-chan description.Topology
   head     *Node
   tail     *Node
   timeout  uint32
   mutex    sync.Mutex // mutex to protect list and sessionTimeout

   checkedOut int // number of sessions checked out of pool
}



vendor/go.mongodb.org/mongo-driver/x/mongo/driver/session/session_pool.go:103

// ReturnSession returns a session to the pool if it has not expired.
func (p *Pool) ReturnSession(ss *Server) {
   if ss == nil {
      return
   }

   p.mutex.Lock()
   defer p.mutex.Unlock()

   p.checkedOut--
   p.updateTimeout()
   // check sessions at end of queue for expired
   // stop checking after hitting the first valid session
   for p.tail != nil && p.tail.expired(p.timeout) {
      if p.tail.prev != nil {
         p.tail.prev.next = nil
      }
      p.tail = p.tail.prev
   }

   // session expired
   if ss.expired(p.timeout) {
      return
   }

   // session is dirty
   if ss.Dirty {
      return
   }

   newNode := &Node{
      Server: ss,
      next:   nil,
      prev:   nil,
   }

   // empty list
   if p.tail == nil {
      p.head = newNode
      p.tail = newNode
      return
   }

   // at least 1 valid session in list
   newNode.next = p.head
   p.head.prev = newNode
   p.head = newNode
}