mirror of https://github.com/prometheus/prometheus
49 lines
1.3 KiB
Go
49 lines
1.3 KiB
Go
|
// Copyright 2016 The Prometheus Authors
|
||
|
|
// 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 gate
|
||
|
|
|
||
|
|
import "context"
|
||
|
|
|
||
|
|
// A Gate controls the maximum number of concurrently running and waiting queries.
|
||
|
|
type Gate struct {
|
||
|
|
ch chan struct{}
|
||
|
|
}
|
||
|
|
|
||
|
|
// New returns a query gate that limits the number of queries
|
||
|
|
// being concurrently executed.
|
||
|
|
func New(length int) *Gate {
|
||
|
|
return &Gate{
|
||
|
|
ch: make(chan struct{}, length),
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
// Start blocks until the gate has a free spot or the context is done.
|
||
|
|
func (g *Gate) Start(ctx context.Context) error {
|
||
|
|
select {
|
||
|
|
case <-ctx.Done():
|
||
|
|
return ctx.Err()
|
||
|
|
case g.ch <- struct{}{}:
|
||
|
|
return nil
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
// Done releases a single spot in the gate.
|
||
|
|
func (g *Gate) Done() {
|
||
|
|
select {
|
||
|
|
case <-g.ch:
|
||
|
|
default:
|
||
|
|
panic("gate.Done: more operations done than started")
|
||
|
|
}
|
||
|
|
}
|