zitadel/internal/eventstore/handler/crdb/lock.go

package crdb

import (
	"context"
	"database/sql"
	"fmt"
	"os"
	"time"

	"github.com/caos/logging"

	"github.com/caos/zitadel/internal/errors"
	"github.com/caos/zitadel/internal/id"
)

const (
	lockStmtFormat = "INSERT INTO %[1]s" +
		" (locker_id, locked_until, projection_name, instance_id) VALUES ($1, now()+$2::INTERVAL, $3, $4)" +
		" ON CONFLICT (projection_name, instance_id)" +
		" DO UPDATE SET locker_id = $1, locked_until = now()+$2::INTERVAL" +
		" WHERE %[1]s.projection_name = $3 AND %[1]s.instance_id = $4 AND (%[1]s.locker_id = $1 OR %[1]s.locked_until < now())"
)

type Locker interface {
	Lock(ctx context.Context, lockDuration time.Duration, instanceID string) <-chan error
	Unlock(instanceID string) error
}

type locker struct {
	client         *sql.DB
	lockStmt       string
	workerName     string
	projectionName string
}

func NewLocker(client *sql.DB, lockTable, projectionName string) Locker {
	workerName, err := os.Hostname()
	if err != nil || workerName == "" {
		workerName, err = id.SonyFlakeGenerator.Next()
		logging.OnError(err).Panic("unable to generate lockID")
	}
	return &locker{
		client:         client,
		lockStmt:       fmt.Sprintf(lockStmtFormat, lockTable),
		workerName:     workerName,
		projectionName: projectionName,
	}
}

func (h *locker) Lock(ctx context.Context, lockDuration time.Duration, instanceID string) <-chan error {
	errs := make(chan error)
	go h.handleLock(ctx, errs, lockDuration, instanceID)
	return errs
}

func (h *locker) handleLock(ctx context.Context, errs chan error, lockDuration time.Duration, instanceID string) {
	renewLock := time.NewTimer(0)
	for {
		select {
		case <-renewLock.C:
			errs <- h.renewLock(ctx, lockDuration, instanceID)
			//refresh the lock 500ms before it times out. 500ms should be enough for one transaction
			renewLock.Reset(lockDuration - (500 * time.Millisecond))
		case <-ctx.Done():
			close(errs)
			renewLock.Stop()
			return
		}
	}
}

func (h *locker) renewLock(ctx context.Context, lockDuration time.Duration, instanceID string) error {
	//the unit of crdb interval is seconds (https://www.cockroachlabs.com/docs/stable/interval.html).
	res, err := h.client.Exec(h.lockStmt, h.workerName, lockDuration.Seconds(), h.projectionName, instanceID)
	if err != nil {
		return errors.ThrowInternal(err, "CRDB-uaDoR", "unable to execute lock")
	}

	if rows, _ := res.RowsAffected(); rows == 0 {
		return errors.ThrowAlreadyExists(nil, "CRDB-mmi4J", "projection already locked")
	}

	return nil
}

func (h *locker) Unlock(instanceID string) error {
	_, err := h.client.Exec(h.lockStmt, h.workerName, float64(0), h.projectionName, instanceID)
	if err != nil {
		return errors.ThrowUnknown(err, "CRDB-JjfwO", "unlock failed")
	}
	return nil
}