pool.go

// Package qidpool manages pools of 9P Qids, 13-bit unique identifiers
// for files.
package qidpool

import (
	"sync/atomic"

	"aqwari.net/net/styx/internal/threadsafe"
	"aqwari.net/net/styx/styxproto"
)

// A Pool maintains a pool of unique 13-bit identifiers
// for files on a 9P file server. A Pool must be created
// with a call to New.
type Pool struct {
	m    *threadsafe.Map
	path uint64
}

// New returns a new, empty Pool.
func New() *Pool {
	return &Pool{m: threadsafe.NewMap()}
}

// Put creates a new, unique Qid of the given type and adds it to the
// pool. The returned Qid should be considered read-only. Put will not
// overwrite an existing Qid; if there is already a Qid associated with name,
// it is returned instead.
func (p *Pool) Put(name string, qtype uint8) styxproto.Qid {
	buf := make([]byte, styxproto.QidLen)
	path := atomic.AddUint64(&p.path, 1)

	qid, _, err := styxproto.NewQid(buf, qtype, 0, path)
	if err != nil {
		panic(err)
	}

	p.m.Do(func(m map[interface{}]interface{}) {
		if existing, ok := m[name]; ok {
			qid = existing.(styxproto.Qid)
		} else {
			m[name] = qid
		}
	})
	p.m.Put(name, qid)
	return qid
}

// Del removes a Qid from a Pool. Once a Qid is removed from a pool, it
// will never be used again.
func (p *Pool) Del(name string) {
	p.m.Del(name)
}

// Do calls fn while holding the write lock for the pool
func (p *Pool) Do(fn func(map[interface{}]interface{})) {
	p.m.Do(fn)
}

// Get fetches the Qid currently associated with name from the pool. The
// Qid is only valid if the second return value is true.
func (p *Pool) Get(name string) (styxproto.Qid, bool) {
	if v, ok := p.m.Get(name); ok {
		return v.(styxproto.Qid), true
	}
	return nil, false
}