86 lines
1.5 KiB
Go
86 lines
1.5 KiB
Go
package scheduler
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import (
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"context"
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"errors"
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"fmt"
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"log/slog"
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"math/rand"
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"time"
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"github.com/jackc/pgx/v5"
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)
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type Scheduler struct {
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logger *slog.Logger
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db *pgx.Conn
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}
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func NewScheduler(logger *slog.Logger, db *pgx.Conn) *Scheduler {
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return &Scheduler{
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logger: logger,
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db: db,
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}
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}
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func (s *Scheduler) Execute(ctx context.Context) error {
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acquiredLeader, err := s.acquireLeader(ctx)
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if err != nil {
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return err
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}
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if !acquiredLeader {
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s.logger.Info("gracefully shutting down non-elected scheduler")
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return nil
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}
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for {
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select {
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case <-ctx.Done():
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s.logger.Info("gracefully shutting down elected scheduler")
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return nil
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default:
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if err := s.process(ctx); err != nil {
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return fmt.Errorf("scheduler failed: %w", err)
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}
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}
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}
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}
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func (s *Scheduler) acquireLeader(ctx context.Context) (bool, error) {
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for {
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select {
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case <-ctx.Done():
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return false, nil
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default:
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var acquiredLock bool
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if err := s.db.QueryRow(ctx, "SELECT pg_try_advisory_lock(1234)").Scan(&acquiredLock); err != nil {
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if errors.Is(err, pgx.ErrNoRows) {
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return false, nil
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}
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}
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if !acquiredLock {
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wait := time.Second * time.Duration(rand.Float32()*9+1)
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s.logger.Debug("failed to acquire lock, parking non-elected scheduler", "wait_seconds", wait)
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time.Sleep(wait)
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continue
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}
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return true, nil
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}
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}
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}
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func (s *Scheduler) process(ctx context.Context) error {
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s.logger.Debug("scheduler processing items")
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// FIXME: simulate work
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time.Sleep(time.Second * 2)
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return nil
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}
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