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Merge pull request #8998 from hashicorp/dnephin/lib-ttlcache

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lib/ttlcache: extract a new package from agent/cache
This commit is contained in:
Daniel Nephin 2020-10-27 16:43:10 -04:00 committed by GitHub
parent 87a43b0ba7 09d62f1df0
commit a0e017791f
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
6 changed files with 379 additions and 250 deletions
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56
agent/cache/cache.go vendored
View file

@ -15,7 +15,6 @@
package cache
import (
"container/heap"
"context"
"fmt"
"io"
@ -28,6 +27,7 @@ import (
"golang.org/x/time/rate"
"github.com/hashicorp/consul/lib"
"github.com/hashicorp/consul/lib/ttlcache"
)
//go:generate mockery -all -inpkg
@ -88,7 +88,7 @@ type Cache struct {
// internal storage format so changing this should be possible safely.
entriesLock sync.RWMutex
entries map[string]cacheEntry
entriesExpiryHeap *expiryHeap
entriesExpiryHeap *ttlcache.ExpiryHeap
// stopped is used as an atomic flag to signal that the Cache has been
// discarded so background fetches and expiry processing should stop.
@ -166,16 +166,11 @@ func applyDefaultValuesOnOptions(options Options) Options {
// Further settings can be tweaked on the returned value.
func New(options Options) *Cache {
options = applyDefaultValuesOnOptions(options)
// Initialize the heap. The buffer of 1 is really important because
// its possible for the expiry loop to trigger the heap to update
// itself and it'd block forever otherwise.
h := &expiryHeap{NotifyCh: make(chan struct{}, 1)}
heap.Init(h)
ctx, cancel := context.WithCancel(context.Background())
c := &Cache{
types: make(map[string]typeEntry),
entries: make(map[string]cacheEntry),
entriesExpiryHeap: h,
entriesExpiryHeap: ttlcache.NewExpiryHeap(),
stopCh: make(chan struct{}),
options: options,
rateLimitContext: ctx,
@ -406,8 +401,7 @@ RETRY_GET:
// Touch the expiration and fix the heap.
c.entriesLock.Lock()
entry.Expiry.Update(r.TypeEntry.Opts.LastGetTTL)
c.entriesExpiryHeap.Fix(entry.Expiry)
c.entriesExpiryHeap.Update(entry.Expiry.Index(), r.TypeEntry.Opts.LastGetTTL)
c.entriesLock.Unlock()
// We purposely do not return an error here since the cache only works with
@ -688,10 +682,8 @@ func (c *Cache) fetch(key string, r getOptions, allowNew bool, attempt uint, ign
// If this is a new entry (not in the heap yet), then setup the
// initial expiry information and insert. If we're already in
// the heap we do nothing since we're reusing the same entry.
if newEntry.Expiry == nil || newEntry.Expiry.HeapIndex == -1 {
newEntry.Expiry = &cacheEntryExpiry{Key: key}
newEntry.Expiry.Update(tEntry.Opts.LastGetTTL)
heap.Push(c.entriesExpiryHeap, newEntry.Expiry)
if newEntry.Expiry == nil || newEntry.Expiry.Index() == ttlcache.NotIndexed {
newEntry.Expiry = c.entriesExpiryHeap.Add(key, tEntry.Opts.LastGetTTL)
}
c.entries[key] = newEntry
@ -748,47 +740,30 @@ func backOffWait(failures uint) time.Duration {
// runExpiryLoop is a blocking function that watches the expiration
// heap and invalidates entries that have expired.
func (c *Cache) runExpiryLoop() {
var expiryTimer *time.Timer
for {
// If we have a previous timer, stop it.
if expiryTimer != nil {
expiryTimer.Stop()
}
// Get the entry expiring soonest
var entry *cacheEntryExpiry
var expiryCh <-chan time.Time
c.entriesLock.RLock()
if len(c.entriesExpiryHeap.Entries) > 0 {
entry = c.entriesExpiryHeap.Entries[0]
expiryTimer = time.NewTimer(time.Until(entry.Expires))
expiryCh = expiryTimer.C
}
timer := c.entriesExpiryHeap.Next()
c.entriesLock.RUnlock()
select {
case <-c.stopCh:
timer.Stop()
return
case <-c.entriesExpiryHeap.NotifyCh:
// Entries changed, so the heap may have changed. Restart loop.
timer.Stop()
continue
case <-expiryCh:
case <-timer.Wait():
c.entriesLock.Lock()
// Perform cleanup operations on the entry's state, if applicable.
state := c.entries[entry.Key].State
if closer, ok := state.(io.Closer); ok {
entry := timer.Entry
if closer, ok := c.entries[entry.Key()].State.(io.Closer); ok {
closer.Close()
}
// Entry expired! Remove it.
delete(c.entries, entry.Key)
heap.Remove(c.entriesExpiryHeap, entry.HeapIndex)
// This is subtle but important: if we race and simultaneously
// evict and fetch a new value, then we set this to -1 to
// have it treated as a new value so that the TTL is extended.
entry.HeapIndex = -1
delete(c.entries, entry.Key())
c.entriesExpiryHeap.Remove(entry.Index())
// Set some metrics
metrics.IncrCounter([]string{"consul", "cache", "evict_expired"}, 1)
@ -829,7 +804,6 @@ func (c *Cache) Prepopulate(t string, res FetchResult, dc, token, k string) erro
Index: res.Index,
FetchedAt: time.Now(),
Waiter: make(chan struct{}),
Expiry: &cacheEntryExpiry{Key: key},
FetchRateLimiter: rate.NewLimiter(
c.options.EntryFetchRate,
c.options.EntryFetchMaxBurst,

74
agent/cache/cache_test.go vendored
View file

@ -15,6 +15,7 @@ import (
"github.com/stretchr/testify/require"
"golang.org/x/time/rate"
"github.com/hashicorp/consul/lib/ttlcache"
"github.com/hashicorp/consul/sdk/testutil"
)
@ -1000,6 +1001,9 @@ func (t *testPartitionType) RegisterOptions() RegisterOptions {
// Test that background refreshing reports correct Age in failure and happy
// states.
func TestCacheGet_refreshAge(t *testing.T) {
if testing.Short() {
t.Skip("too slow for -short run")
}
t.Parallel()
require := require.New(t)
@ -1402,3 +1406,73 @@ OUT:
}
}
}
func TestCache_ExpiryLoop_ExitsWhenStopped(t *testing.T) {
c := &Cache{
stopCh: make(chan struct{}),
entries: make(map[string]cacheEntry),
entriesExpiryHeap: ttlcache.NewExpiryHeap(),
}
chStart := make(chan struct{})
chDone := make(chan struct{})
go func() {
close(chStart)
c.runExpiryLoop()
close(chDone)
}()
<-chStart
close(c.stopCh)
select {
case <-chDone:
case <-time.After(50 * time.Millisecond):
t.Fatalf("expected loop to exit when stopped")
}
}
func TestCache_Prepopulate(t *testing.T) {
typ := &fakeType{index: 5}
c := New(Options{})
c.RegisterType("t", typ)
c.Prepopulate("t", FetchResult{Value: 17, Index: 1}, "dc1", "token", "v1")
ctx := context.Background()
req := fakeRequest{
info: RequestInfo{
Key: "v1",
Token: "token",
Datacenter: "dc1",
MinIndex: 1,
},
}
result, _, err := c.Get(ctx, "t", req)
require.NoError(t, err)
require.Equal(t, 17, result)
}
type fakeType struct {
index uint64
}
func (f fakeType) Fetch(_ FetchOptions, _ Request) (FetchResult, error) {
idx := atomic.LoadUint64(&f.index)
return FetchResult{Value: int(idx * 2), Index: idx}, nil
}
func (f fakeType) RegisterOptions() RegisterOptions {
return RegisterOptions{Refresh: true}
}
var _ Type = (*fakeType)(nil)
type fakeRequest struct {
info RequestInfo
}
func (f fakeRequest) CacheInfo() RequestInfo {
return f.info
}
var _ Request = (*fakeRequest)(nil)

122
agent/cache/entry.go vendored
View file

@ -1,10 +1,11 @@
package cache
import (
"container/heap"
"time"
"golang.org/x/time/rate"
"github.com/hashicorp/consul/lib/ttlcache"
)
// cacheEntry stores a single cache entry.
@ -31,8 +32,8 @@ type cacheEntry struct {
// Expiry contains information about the expiration of this
// entry. This is a pointer as its shared as a value in the
// expiryHeap as well.
Expiry *cacheEntryExpiry
// ExpiryHeap as well.
Expiry *ttlcache.Entry
// FetchedAt stores the time the cache entry was retrieved for determining
// it's age later.
@ -46,118 +47,3 @@ type cacheEntry struct {
// FetchRateLimiter limits the rate at which fetch is called for this entry.
FetchRateLimiter *rate.Limiter
}
// cacheEntryExpiry contains the expiration information for a cache
// entry. Any modifications to this struct should be done only while
// the Cache entriesLock is held.
type cacheEntryExpiry struct {
Key string // Key in the cache map
Expires time.Time // Time when entry expires (monotonic clock)
HeapIndex int // Index in the heap
}
// Update the expiry to d time from now.
func (e *cacheEntryExpiry) Update(d time.Duration) {
e.Expires = time.Now().Add(d)
}
// expiryHeap is a heap implementation that stores information about
// when entries expire. Implements container/heap.Interface.
//
// All operations on the heap and read/write of the heap contents require
// the proper entriesLock to be held on Cache.
type expiryHeap struct {
Entries []*cacheEntryExpiry
// NotifyCh is sent a value whenever the 0 index value of the heap
// changes. This can be used to detect when the earliest value
// changes.
//
// There is a single edge case where the heap will not automatically
// send a notification: if heap.Fix is called manually and the index
// changed is 0 and the change doesn't result in any moves (stays at index
// 0), then we won't detect the change. To work around this, please
// always call the expiryHeap.Fix method instead.
NotifyCh chan struct{}
}
// Identical to heap.Fix for this heap instance but will properly handle
// the edge case where idx == 0 and no heap modification is necessary,
// and still notify the NotifyCh.
//
// This is important for cache expiry since the expiry time may have been
// extended and if we don't send a message to the NotifyCh then we'll never
// reset the timer and the entry will be evicted early.
func (h *expiryHeap) Fix(entry *cacheEntryExpiry) {
idx := entry.HeapIndex
heap.Fix(h, idx)
// This is the edge case we handle: if the prev (idx) and current (HeapIndex)
// is zero, it means the head-of-line didn't change while the value
// changed. Notify to reset our expiry worker.
if idx == 0 && entry.HeapIndex == 0 {
h.notify()
}
}
func (h *expiryHeap) Len() int { return len(h.Entries) }
func (h *expiryHeap) Swap(i, j int) {
h.Entries[i], h.Entries[j] = h.Entries[j], h.Entries[i]
h.Entries[i].HeapIndex = i
h.Entries[j].HeapIndex = j
// If we're moving the 0 index, update the channel since we need
// to re-update the timer we're waiting on for the soonest expiring
// value.
if i == 0 || j == 0 {
h.notify()
}
}
func (h *expiryHeap) Less(i, j int) bool {
// The usage of Before here is important (despite being obvious):
// this function uses the monotonic time that should be available
// on the time.Time value so the heap is immune to wall clock changes.
return h.Entries[i].Expires.Before(h.Entries[j].Expires)
}
// heap.Interface, this isn't expected to be called directly.
func (h *expiryHeap) Push(x interface{}) {
entry := x.(*cacheEntryExpiry)
// Set initial heap index, if we're going to the end then Swap
// won't be called so we need to initialize
entry.HeapIndex = len(h.Entries)
// For the first entry, we need to trigger a channel send because
// Swap won't be called; nothing to swap! We can call it right away
// because all heap operations are within a lock.
if len(h.Entries) == 0 {
h.notify()
}
h.Entries = append(h.Entries, entry)
}
// heap.Interface, this isn't expected to be called directly.
func (h *expiryHeap) Pop() interface{} {
old := h.Entries
n := len(old)
x := old[n-1]
h.Entries = old[0 : n-1]
return x
}
func (h *expiryHeap) notify() {
select {
case h.NotifyCh <- struct{}{}:
// Good
default:
// If the send would've blocked, we just ignore it. The reason this
// is safe is because NotifyCh should always be a buffered channel.
// If this blocks, it means that there is a pending message anyways
// so the receiver will restart regardless.
}
}

91
agent/cache/entry_test.go vendored
View file

@ -1,91 +0,0 @@
package cache
import (
"container/heap"
"testing"
"time"
"github.com/stretchr/testify/require"
)
func TestExpiryHeap_impl(t *testing.T) {
var _ heap.Interface = new(expiryHeap)
}
func TestExpiryHeap(t *testing.T) {
require := require.New(t)
now := time.Now()
ch := make(chan struct{}, 10) // buffered to prevent blocking in tests
h := &expiryHeap{NotifyCh: ch}
// Init, shouldn't trigger anything
heap.Init(h)
testNoMessage(t, ch)
// Push an initial value, expect one message
entry := &cacheEntryExpiry{Key: "foo", HeapIndex: -1, Expires: now.Add(100)}
heap.Push(h, entry)
require.Equal(0, entry.HeapIndex)
testMessage(t, ch)
testNoMessage(t, ch) // exactly one asserted above
// Push another that goes earlier than entry
entry2 := &cacheEntryExpiry{Key: "bar", HeapIndex: -1, Expires: now.Add(50)}
heap.Push(h, entry2)
require.Equal(0, entry2.HeapIndex)
require.Equal(1, entry.HeapIndex)
testMessage(t, ch)
testNoMessage(t, ch) // exactly one asserted above
// Push another that goes at the end
entry3 := &cacheEntryExpiry{Key: "bar", HeapIndex: -1, Expires: now.Add(1000)}
heap.Push(h, entry3)
require.Equal(2, entry3.HeapIndex)
testNoMessage(t, ch) // no notify cause index 0 stayed the same
// Remove the first entry (not Pop, since we don't use Pop, but that works too)
remove := h.Entries[0]
heap.Remove(h, remove.HeapIndex)
require.Equal(0, entry.HeapIndex)
require.Equal(1, entry3.HeapIndex)
testMessage(t, ch)
testMessage(t, ch) // we have two because two swaps happen
testNoMessage(t, ch)
// Let's change entry 3 to be early, and fix it
entry3.Expires = now.Add(10)
h.Fix(entry3)
require.Equal(1, entry.HeapIndex)
require.Equal(0, entry3.HeapIndex)
testMessage(t, ch)
testNoMessage(t, ch)
// Let's change entry 3 again, this is an edge case where if the 0th
// element changed, we didn't trigger the channel. Our Fix func should.
entry.Expires = now.Add(20)
h.Fix(entry3)
require.Equal(1, entry.HeapIndex) // no move
require.Equal(0, entry3.HeapIndex)
testMessage(t, ch)
testNoMessage(t, ch) // one message
}
func testNoMessage(t *testing.T, ch <-chan struct{}) {
t.Helper()
select {
case <-ch:
t.Fatal("should not have a message")
default:
}
}
func testMessage(t *testing.T, ch <-chan struct{}) {
t.Helper()
select {
case <-ch:
default:
t.Fatal("should have a message")
}
}

195
lib/ttlcache/eviction.go Normal file
View file

@ -0,0 +1,195 @@
/*
Package ttlcache provides an ExpiryHeap that can be used by a cache to track the
expiration time of its entries. When an expiry is reached the Timer will fire
and the entry can be removed.
*/
package ttlcache
import (
"container/heap"
"time"
)
// Entry in the ExpiryHeap, tracks the index and expiry time of an item in a
// ttl cache.
type Entry struct {
key string
expiry time.Time
heapIndex int
}
// NotIndexed indicates that the entry does not exist in the heap. Either because
// it is nil, or because it was removed.
const NotIndexed = -1
// Index returns the index of this entry within the heap.
func (e *Entry) Index() int {
if e == nil {
return NotIndexed
}
return e.heapIndex
}
// Key returns the key for the entry in the heap.
func (e *Entry) Key() string {
return e.key
}
// ExpiryHeap is a heap that is ordered by the expiry time of entries. It may
// be used by a cache or storage to expiry items after a TTL.
//
// ExpiryHeap expects the caller to synchronize calls to most of its methods. This
// is necessary because the cache needs to ensure that updates to both its
// storage and the ExpiryHeap are synchronized.
type ExpiryHeap struct {
entries []*Entry
// NotifyCh is sent a value whenever the 0 index value of the heap
// changes. This can be used to detect when the earliest value
// changes.
NotifyCh chan struct{}
}
// NewExpiryHeap creates and returns a new ExpiryHeap.
func NewExpiryHeap() *ExpiryHeap {
h := &ExpiryHeap{NotifyCh: make(chan struct{}, 1)}
heap.Init((*entryHeap)(h))
return h
}
// Add an entry to the heap.
//
// Must be synchronized by the caller.
func (h *ExpiryHeap) Add(key string, expiry time.Duration) *Entry {
entry := &Entry{
key: key,
expiry: time.Now().Add(expiry),
// Set the initial heap index to the last index. If the entry is swapped it
// will have the correct index set, and if it remains at the end the last
// index will be correct.
heapIndex: len(h.entries),
}
heap.Push((*entryHeap)(h), entry)
if entry.heapIndex == 0 {
h.notify()
}
return entry
}
// Update the entry that is currently at idx with the new expiry time. The heap
// will be rebalanced after the entry is updated.
//
// Must be synchronized by the caller.
func (h *ExpiryHeap) Update(idx int, expiry time.Duration) {
if idx == NotIndexed {
// the previous entry did not have a valid index, its not in the heap
return
}
entry := h.entries[idx]
entry.expiry = time.Now().Add(expiry)
heap.Fix((*entryHeap)(h), idx)
// If the previous index and current index are both zero then Fix did not
// swap the entry, and notify must be called here.
if idx == 0 || entry.heapIndex == 0 {
h.notify()
}
}
// Remove the entry at idx from the heap.
//
// Must be synchronized by the caller.
func (h *ExpiryHeap) Remove(idx int) {
entry := h.entries[idx]
heap.Remove((*entryHeap)(h), idx)
// A goroutine which is fetching a new value will have a reference to this
// entry. When it re-acquires the lock it needs to be informed that
// the entry was expired while it was fetching. Setting heapIndex to -1
// indicates that the entry is no longer in the heap, and must be re-added.
entry.heapIndex = NotIndexed
if idx == 0 {
h.notify()
}
}
type entryHeap ExpiryHeap
func (h *entryHeap) Len() int { return len(h.entries) }
func (h *entryHeap) Swap(i, j int) {
h.entries[i], h.entries[j] = h.entries[j], h.entries[i]
h.entries[i].heapIndex = i
h.entries[j].heapIndex = j
}
func (h *entryHeap) Less(i, j int) bool {
// The usage of Before here is important (despite being obvious):
// this function uses the monotonic time that should be available
// on the time.Time value so the heap is immune to wall clock changes.
return h.entries[i].expiry.Before(h.entries[j].expiry)
}
// heap.Interface, this isn't expected to be called directly.
func (h *entryHeap) Push(x interface{}) {
h.entries = append(h.entries, x.(*Entry))
}
// heap.Interface, this isn't expected to be called directly.
func (h *entryHeap) Pop() interface{} {
n := len(h.entries)
entries := h.entries
last := entries[n-1]
h.entries = entries[0 : n-1]
return last
}
// notify the timer that the head value has changed, so the expiry time has
// also likely changed.
func (h *ExpiryHeap) notify() {
// Send to channel without blocking. Skips sending if there is already
// an item in the buffered channel.
select {
case h.NotifyCh <- struct{}{}:
default:
}
}
// Next returns a Timer that waits until the first entry in the heap expires.
//
// Must be synchronized by the caller.
func (h *ExpiryHeap) Next() Timer {
if len(h.entries) == 0 {
return Timer{}
}
entry := h.entries[0]
return Timer{
timer: time.NewTimer(time.Until(entry.expiry)),
Entry: entry,
}
}
// Timer provides a channel to block on. When the Wait channel receives an
// item the Timer.Entry has expired. The caller is expected to call
// ExpiryHeap.Remove with the Entry.Index().
//
// The caller is responsible for calling Stop to stop the timer if the timer has
// not fired.
type Timer struct {
timer *time.Timer
Entry *Entry
}
func (t *Timer) Wait() <-chan time.Time {
if t.timer == nil {
return nil
}
return t.timer.C
}
func (t *Timer) Stop() {
if t.timer != nil {
t.timer.Stop()
}
}

91
lib/ttlcache/eviction_test.go Normal file
View file

@ -0,0 +1,91 @@
package ttlcache
import (
"container/heap"
"testing"
"time"
"github.com/stretchr/testify/assert"
)
var _ heap.Interface = (*entryHeap)(nil)
func TestExpiryHeap(t *testing.T) {
h := NewExpiryHeap()
ch := h.NotifyCh
var entry, entry2, entry3 *Entry
// Init, shouldn't trigger anything
testNoMessage(t, ch)
runStep(t, "add an entry", func(t *testing.T) {
entry = h.Add("foo", 100*time.Millisecond)
assert.Equal(t, 0, entry.heapIndex)
testMessage(t, ch)
testNoMessage(t, ch) // exactly one asserted above
})
runStep(t, "add a second entry in front", func(t *testing.T) {
entry2 = h.Add("bar", 50*time.Millisecond)
assert.Equal(t, 0, entry2.heapIndex)
assert.Equal(t, 1, entry.heapIndex)
testMessage(t, ch)
testNoMessage(t, ch) // exactly one asserted above
})
runStep(t, "add a third entry at the end", func(t *testing.T) {
entry3 = h.Add("baz", 1000*time.Millisecond)
assert.Equal(t, 2, entry3.heapIndex)
testNoMessage(t, ch) // no notify cause index 0 stayed the same
})
runStep(t, "remove the first entry", func(t *testing.T) {
h.Remove(0)
assert.Equal(t, 0, entry.heapIndex)
assert.Equal(t, 1, entry3.heapIndex)
testMessage(t, ch)
testNoMessage(t, ch)
})
runStep(t, "update entry3 to expire first", func(t *testing.T) {
h.Update(entry3.heapIndex, 10*time.Millisecond)
assert.Equal(t, 1, entry.heapIndex)
assert.Equal(t, 0, entry3.heapIndex)
testMessage(t, ch)
testNoMessage(t, ch)
})
runStep(t, "0th element change triggers a notify", func(t *testing.T) {
h.Update(entry3.heapIndex, 20)
assert.Equal(t, 1, entry.heapIndex) // no move
assert.Equal(t, 0, entry3.heapIndex)
testMessage(t, ch)
testNoMessage(t, ch) // one message
})
}
func testNoMessage(t *testing.T, ch <-chan struct{}) {
t.Helper()
select {
case <-ch:
t.Fatal("should not have a message")
default:
}
}
func testMessage(t *testing.T, ch <-chan struct{}) {
t.Helper()
select {
case <-ch:
default:
t.Fatal("should have a message")
}
}
func runStep(t *testing.T, name string, fn func(t *testing.T)) {
if !t.Run(name, fn) {
t.FailNow()
}
}