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background_threads.go
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background_threads.go
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// Copyright 2021 Dolthub, Inc.
//
// 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 sql
import (
"context"
"errors"
"sync"
)
var ErrCannotAddToClosedBackgroundThreads = errors.New("cannot add to a close background threads instance")
type BackgroundThreads struct {
wg *sync.WaitGroup
mu *sync.Mutex
parentCtx context.Context
parentCancel context.CancelFunc
nameToCancel map[string]context.CancelFunc
nameToCtx map[string]context.Context
}
func NewBackgroundThreads() *BackgroundThreads {
ctx, cancel := context.WithCancel(context.Background())
return &BackgroundThreads{
wg: &sync.WaitGroup{},
parentCtx: ctx,
parentCancel: cancel,
mu: &sync.Mutex{},
nameToCancel: make(map[string]context.CancelFunc),
nameToCtx: make(map[string]context.Context),
}
}
// Add starts a background goroutine wrapped by a top-level sync.WaitGroup.
// [f] must return when its [ctx] argument is cancelled, otherwise
// Shutdown will hang.
func (bt *BackgroundThreads) Add(name string, f func(ctx context.Context)) error {
select {
case <-bt.parentCtx.Done():
return ErrCannotAddToClosedBackgroundThreads
default:
}
threadCtx, threadCancel := context.WithCancel(bt.parentCtx)
bt.mu.Lock()
defer bt.mu.Unlock()
bt.nameToCancel[name] = threadCancel
bt.nameToCtx[name] = threadCtx
bt.wg.Add(1)
go func() {
defer bt.wg.Done()
f(threadCtx)
}()
return nil
}
// Shutdown cancels the parent context for every async thread,
// and waits for each goroutine to drain and return before exiting.
func (bt *BackgroundThreads) Shutdown() error {
bt.parentCancel()
bt.wg.Wait()
return bt.parentCtx.Err()
}