hugo/tpl/partials/partials.go
Bjørn Erik Pedersen 929808190f tpl/partials: Fix recently introduced deadlock in partials cache
The change in lock logic for `partialCached` in  0927cf739f was naive as it didn't consider cached partials calling other cached partials.

This changeset may look on the large side for this particular issue, but it pulls in part of a working branch, introducing `context.Context` in the template execution.

Note that the context is only partially implemented in this PR, but the upcoming use cases will, as one example, include having access to the top "dot" (e.g. `Page`) all the way down into partials and shortcodes etc.

The earlier benchmarks rerun against master:

```bash
name              old time/op    new time/op    delta
IncludeCached-10    13.6ms ± 2%    13.8ms ± 1%    ~     (p=0.343 n=4+4)

name              old alloc/op   new alloc/op   delta
IncludeCached-10    5.30MB ± 0%    5.35MB ± 0%  +0.96%  (p=0.029 n=4+4)

name              old allocs/op  new allocs/op  delta
IncludeCached-10     74.7k ± 0%     75.3k ± 0%  +0.77%  (p=0.029 n=4+4)
```

Fixes #9519
2022-02-17 18:47:36 +01:00

277 lines
6.9 KiB
Go

// Copyright 2017 The Hugo Authors. All rights reserved.
//
// 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 partials provides template functions for working with reusable
// templates.
package partials
import (
"context"
"errors"
"fmt"
"html/template"
"io"
"io/ioutil"
"reflect"
"strings"
"sync"
"time"
texttemplate "github.com/gohugoio/hugo/tpl/internal/go_templates/texttemplate"
"github.com/gohugoio/hugo/helpers"
"github.com/gohugoio/hugo/tpl"
bp "github.com/gohugoio/hugo/bufferpool"
"github.com/gohugoio/hugo/deps"
)
// TestTemplateProvider is global deps.ResourceProvider.
// NOTE: It's currently unused.
var TestTemplateProvider deps.ResourceProvider
type partialCacheKey struct {
name string
variant interface{}
}
func (k partialCacheKey) templateName() string {
if !strings.HasPrefix(k.name, "partials/") {
return "partials/" + k.name
}
return k.name
}
// partialCache represents a cache of partials protected by a mutex.
type partialCache struct {
sync.RWMutex
p map[partialCacheKey]interface{}
}
func (p *partialCache) clear() {
p.Lock()
defer p.Unlock()
p.p = make(map[partialCacheKey]interface{})
}
// New returns a new instance of the templates-namespaced template functions.
func New(deps *deps.Deps) *Namespace {
cache := &partialCache{p: make(map[partialCacheKey]interface{})}
deps.BuildStartListeners.Add(
func() {
cache.clear()
})
return &Namespace{
deps: deps,
cachedPartials: cache,
}
}
// Namespace provides template functions for the "templates" namespace.
type Namespace struct {
deps *deps.Deps
cachedPartials *partialCache
}
// contextWrapper makes room for a return value in a partial invocation.
type contextWrapper struct {
Arg interface{}
Result interface{}
}
// Set sets the return value and returns an empty string.
func (c *contextWrapper) Set(in interface{}) string {
c.Result = in
return ""
}
// Include executes the named partial.
// If the partial contains a return statement, that value will be returned.
// Else, the rendered output will be returned:
// A string if the partial is a text/template, or template.HTML when html/template.
// Note that ctx is provided by Hugo, not the end user.
func (ns *Namespace) Include(ctx context.Context, name string, contextList ...interface{}) (interface{}, error) {
name, result, err := ns.include(ctx, name, contextList...)
if err != nil {
return result, err
}
if ns.deps.Metrics != nil {
ns.deps.Metrics.TrackValue(name, result, false)
}
return result, nil
}
// include is a helper function that lookups and executes the named partial.
// Returns the final template name and the rendered output.
func (ns *Namespace) include(ctx context.Context, name string, dataList ...interface{}) (string, interface{}, error) {
var data interface{}
if len(dataList) > 0 {
data = dataList[0]
}
var n string
if strings.HasPrefix(name, "partials/") {
n = name
} else {
n = "partials/" + name
}
templ, found := ns.deps.Tmpl().Lookup(n)
if !found {
// For legacy reasons.
templ, found = ns.deps.Tmpl().Lookup(n + ".html")
}
if !found {
return "", "", fmt.Errorf("partial %q not found", name)
}
var info tpl.ParseInfo
if ip, ok := templ.(tpl.Info); ok {
info = ip.ParseInfo()
}
var w io.Writer
if info.HasReturn {
// Wrap the context sent to the template to capture the return value.
// Note that the template is rewritten to make sure that the dot (".")
// and the $ variable points to Arg.
data = &contextWrapper{
Arg: data,
}
// We don't care about any template output.
w = ioutil.Discard
} else {
b := bp.GetBuffer()
defer bp.PutBuffer(b)
w = b
}
if err := ns.deps.Tmpl().ExecuteWithContext(ctx, templ, w, data); err != nil {
return "", nil, err
}
var result interface{}
if ctx, ok := data.(*contextWrapper); ok {
result = ctx.Result
} else if _, ok := templ.(*texttemplate.Template); ok {
result = w.(fmt.Stringer).String()
} else {
result = template.HTML(w.(fmt.Stringer).String())
}
return templ.Name(), result, nil
}
// IncludeCached executes and caches partial templates. The cache is created with name+variants as the key.
// Note that ctx is provided by Hugo, not the end user.
func (ns *Namespace) IncludeCached(ctx context.Context, name string, context interface{}, variants ...interface{}) (interface{}, error) {
key, err := createKey(name, variants...)
if err != nil {
return nil, err
}
result, err := ns.getOrCreate(ctx, key, context)
if err == errUnHashable {
// Try one more
key.variant = helpers.HashString(key.variant)
result, err = ns.getOrCreate(ctx, key, context)
}
return result, err
}
func createKey(name string, variants ...interface{}) (partialCacheKey, error) {
var variant interface{}
if len(variants) > 1 {
variant = helpers.HashString(variants...)
} else if len(variants) == 1 {
variant = variants[0]
t := reflect.TypeOf(variant)
switch t.Kind() {
// This isn't an exhaustive list of unhashable types.
// There may be structs with slices,
// but that should be very rare. We do recover from that situation
// below.
case reflect.Slice, reflect.Array, reflect.Map:
variant = helpers.HashString(variant)
}
}
return partialCacheKey{name: name, variant: variant}, nil
}
var errUnHashable = errors.New("unhashable")
func (ns *Namespace) getOrCreate(ctx context.Context, key partialCacheKey, context interface{}) (result interface{}, err error) {
start := time.Now()
defer func() {
if r := recover(); r != nil {
err = r.(error)
if strings.Contains(err.Error(), "unhashable type") {
ns.cachedPartials.RUnlock()
err = errUnHashable
}
}
}()
// We may already have a write lock.
hasLock := tpl.GetHasLockFromContext(ctx)
if !hasLock {
ns.cachedPartials.RLock()
}
p, ok := ns.cachedPartials.p[key]
if !hasLock {
ns.cachedPartials.RUnlock()
}
if ok {
if ns.deps.Metrics != nil {
ns.deps.Metrics.TrackValue(key.templateName(), p, true)
// The templates that gets executed is measued in Execute.
// We need to track the time spent in the cache to
// get the totals correct.
ns.deps.Metrics.MeasureSince(key.templateName(), start)
}
return p, nil
}
if !hasLock {
ns.cachedPartials.Lock()
defer ns.cachedPartials.Unlock()
ctx = tpl.SetHasLockInContext(ctx, true)
}
var name string
name, p, err = ns.include(ctx, key.name, context)
if err != nil {
return nil, err
}
if ns.deps.Metrics != nil {
ns.deps.Metrics.TrackValue(name, p, false)
}
ns.cachedPartials.p[key] = p
return p, nil
}