command.go

package lockd

import (
	"context"
	"time"

	"github.com/imharjot/lockd/lease"
)

// op is the kind of command sent to a key actor.
type op int

const (
	opAcquire op = iota
	opRenew
	opRelease
	opExpire // internal, emitted by the timing wheel
	opSnapshot
	opDrain   // internal, prunes cancelled waiters from the queue
	opInstall // internal, restores a recovered lease during WAL replay
)

// result is the reply a caller receives from a command.
type result struct {
	lease lease.Lease
	held  bool
	err   error
}

// command is a single unit of work handed to a key actor. Exactly one actor
// goroutine processes commands for a given key, so the actor body needs no
// locks to mutate its lease.Key.
type command struct {
	op     op
	holder string
	token  lease.Token
	ttl    time.Duration

	// ctx lets a queued acquire be cancelled while it waits its turn.
	ctx context.Context

	// installLease carries a recovered lease for opInstall.
	installLease lease.Lease

	reply chan result
}

func newCommand(o op) *command {
	return &command{op: o, reply: make(chan result, 1)}
}