z/z.go

/*
 * Copyright 2019 Dgraph Labs, Inc. and Contributors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package z

import (
	"context"
	"sync"

	"github.com/cespare/xxhash"
)

// TODO: Figure out a way to re-use memhash for the second uint64 hash, we
//       already know that appending bytes isn't reliable for generating a
//       second hash (see Ristretto PR #88).
//
//       We also know that while the Go runtime has a runtime memhash128
//       function, it's not possible to use it to generate [2]uint64 or
//       anything resembling a 128bit hash, even though that's exactly what
//       we need in this situation.
func KeyToHash(key interface{}) (uint64, uint64) {
	if key == nil {
		return 0, 0
	}
	switch k := key.(type) {
	case uint64:
		return k, 0
	case string:
		return MemHashString(k), xxhash.Sum64String(k)
	case []byte:
		return MemHash(k), xxhash.Sum64(k)
	case byte:
		return uint64(k), 0
	case int:
		return uint64(k), 0
	case int32:
		return uint64(k), 0
	case uint32:
		return uint64(k), 0
	case int64:
		return uint64(k), 0
	default:
		panic("Key type not supported")
	}
}

var (
	dummyCloserChan <-chan struct{}
)

// Closer holds the two things we need to close a goroutine and wait for it to
// finish: a chan to tell the goroutine to shut down, and a WaitGroup with
// which to wait for it to finish shutting down.
type Closer struct {
	waiting sync.WaitGroup

	ctx    context.Context
	cancel context.CancelFunc
}

// NewCloser constructs a new Closer, with an initial count on the WaitGroup.
func NewCloser(initial int) *Closer {
	ret := &Closer{}
	ret.ctx, ret.cancel = context.WithCancel(context.Background())
	ret.waiting.Add(initial)
	return ret
}

// AddRunning Add()'s delta to the WaitGroup.
func (lc *Closer) AddRunning(delta int) {
	lc.waiting.Add(delta)
}

// Ctx can be used to get a context, which would automatically get cancelled when Signal is called.
func (lc *Closer) Ctx() context.Context {
	if lc == nil {
		return context.Background()
	}
	return lc.ctx
}

// Signal signals the HasBeenClosed signal.
func (lc *Closer) Signal() {
	// Todo(ibrahim): Change Signal to return error on next badger breaking change.
	lc.cancel()
}

// HasBeenClosed gets signaled when Signal() is called.
func (lc *Closer) HasBeenClosed() <-chan struct{} {
	if lc == nil {
		return dummyCloserChan
	}
	return lc.ctx.Done()
}

// Done calls Done() on the WaitGroup.
func (lc *Closer) Done() {
	if lc == nil {
		return
	}
	lc.waiting.Done()
}

// Wait waits on the WaitGroup. (It waits for NewCloser's initial value, AddRunning, and Done
// calls to balance out.)
func (lc *Closer) Wait() {
	lc.waiting.Wait()
}

// SignalAndWait calls Signal(), then Wait().
func (lc *Closer) SignalAndWait() {
	lc.Signal()
	lc.Wait()
}

// ZeroOut zeroes out all the bytes in the range [start, end).
func ZeroOut(dst []byte, start, end int) {
	if start < 0 || start >= len(dst) {
		return // BAD
	}
	if end >= len(dst) {
		end = len(dst)
	}
	if end-start <= 0 {
		return
	}
	b := dst[start:end]
	for i := range b {
		b[i] = 0x0
	}
}