GoToSocial/internal/cache/util.go

// GoToSocial
// Copyright (C) GoToSocial Authors admin@gotosocial.org
// SPDX-License-Identifier: AGPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package cache

import (
	"context"
	"errors"
	"fmt"
	"time"

	"codeberg.org/gruf/go-cache/v3/result"
	errorsv2 "codeberg.org/gruf/go-errors/v2"
	"github.com/superseriousbusiness/gotosocial/internal/log"
)

// SentinelError is returned to indicate a non-permanent error return,
// i.e. a situation in which we do not want a cache a negative result.
var SentinelError = errors.New("BUG: error should not be returned") //nolint:revive

// ignoreErrors is an error ignoring function capable of being passed to
// caches, which specifically catches and ignores our sentinel error type.
func ignoreErrors(err error) bool {
	return errorsv2.Comparable(
		err,
		SentinelError,
		context.DeadlineExceeded,
		context.Canceled,
	)
}

// nocopy when embedded will signal linter to
// error on pass-by-value of parent struct.
type nocopy struct{}

func (*nocopy) Lock() {}

func (*nocopy) Unlock() {}

// tryStart will attempt to start the given cache only if sweep duration > 0 (sweeping is enabled).
func tryStart[ValueType any](cache *result.Cache[ValueType], sweep time.Duration) {
	if sweep > 0 {
		var z ValueType
		msg := fmt.Sprintf("starting %T cache", z)
		tryUntil(msg, 5, func() bool {
			return cache.Start(sweep)
		})
	}
}

// tryStop will attempt to stop the given cache only if sweep duration > 0 (sweeping is enabled).
func tryStop[ValueType any](cache *result.Cache[ValueType], sweep time.Duration) {
	if sweep > 0 {
		var z ValueType
		msg := fmt.Sprintf("stopping %T cache", z)
		tryUntil(msg, 5, cache.Stop)
	}
}

// tryUntil will attempt to call 'do' for 'count' attempts, before panicking with 'msg'.
func tryUntil(msg string, count int, do func() bool) {
	for i := 0; i < count; i++ {
		if do() {
			// success.
			return
		}

		// Sleep for a little before retry (a bcakoff).
		time.Sleep(time.Millisecond * 1 << (i + 1))
	}

	// panic on total failure as this shouldn't happen.
	log.Panicf(nil, "failed %s after %d tries", msg, count)
}