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// Copyright 2019 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 lazy
import (
"context"
"sync"
"time"
"github.com/pkg/errors"
)
// New creates a new empty Init.
func New() *Init {
return &Init{}
}
// Init holds a graph of lazily initialized dependencies.
type Init struct {
mu sync.Mutex
prev *Init
children []*Init
init onceMore
out interface{}
err error
f func() (interface{}, error)
}
// Add adds a func as a new child dependency.
func (ini *Init) Add(initFn func() (interface{}, error)) *Init {
if ini == nil {
ini = New()
}
return ini.add(false, initFn)
}
// AddWithTimeout is same as Add, but with a timeout that aborts initialization.
func (ini *Init) AddWithTimeout(timeout time.Duration, f func(ctx context.Context) (interface{}, error)) *Init {
return ini.Add(func() (interface{}, error) {
return ini.withTimeout(timeout, f)
})
}
// Branch creates a new dependency branch based on an existing and adds
// the given dependency as a child.
func (ini *Init) Branch(initFn func() (interface{}, error)) *Init {
if ini == nil {
ini = New()
}
return ini.add(true, initFn)
}
// BranchdWithTimeout is same as Branch, but with a timeout.
func (ini *Init) BranchdWithTimeout(timeout time.Duration, f func(ctx context.Context) (interface{}, error)) *Init {
return ini.Branch(func() (interface{}, error) {
return ini.withTimeout(timeout, f)
})
}
// Do initializes the entire dependency graph.
func (ini *Init) Do() (interface{}, error) {
if ini == nil {
panic("init is nil")
}
ini.init.Do(func() {
prev := ini.prev
if prev != nil {
// A branch. Initialize the ancestors.
if prev.shouldInitialize() {
_, err := prev.Do()
if err != nil {
ini.err = err
return
}
} else if prev.inProgress() {
// Concurrent initialization. The following init func
// may depend on earlier state, so wait.
prev.wait()
}
}
if ini.f != nil {
ini.out, ini.err = ini.f()
}
for _, child := range ini.children {
if child.shouldInitialize() {
_, err := child.Do()
if err != nil {
ini.err = err
return
}
}
}
})
ini.wait()
return ini.out, ini.err
}
// TODO(bep) investigate if we can use sync.Cond for this.
func (ini *Init) wait() {
var counter time.Duration
for !ini.init.Done() {
counter += 10
if counter > 600000000 {
panic("BUG: timed out in lazy init")
}
time.Sleep(counter * time.Microsecond)
}
}
func (ini *Init) inProgress() bool {
return ini != nil && ini.init.InProgress()
}
func (ini *Init) shouldInitialize() bool {
return !(ini == nil || ini.init.Done() || ini.init.InProgress())
}
// Reset resets the current and all its dependencies.
func (ini *Init) Reset() {
mu := ini.init.ResetWithLock()
defer mu.Unlock()
for _, d := range ini.children {
d.Reset()
}
}
func (ini *Init) add(branch bool, initFn func() (interface{}, error)) *Init {
ini.mu.Lock()
defer ini.mu.Unlock()
if branch {
return &Init{
f: initFn,
prev: ini,
}
}
ini.checkDone()
ini.children = append(ini.children, &Init{
f: initFn,
})
return ini
}
func (ini *Init) checkDone() {
if ini.init.Done() {
panic("init cannot be added to after it has run")
}
}
func (ini *Init) withTimeout(timeout time.Duration, f func(ctx context.Context) (interface{}, error)) (interface{}, error) {
ctx, cancel := context.WithTimeout(context.Background(), timeout)
defer cancel()
c := make(chan verr, 1)
go func() {
v, err := f(ctx)
select {
case <-ctx.Done():
return
default:
c <- verr{v: v, err: err}
}
}()
select {
case <-ctx.Done():
return nil, errors.New("timed out initializing value. This is most likely a circular loop in a shortcode")
case ve := <-c:
return ve.v, ve.err
}
}
type verr struct {
v interface{}
err error
}
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