49 lines
1.3 KiB
Go
49 lines
1.3 KiB
Go
// Copyright 2016 The Prometheus Authors
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package gate
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import "context"
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// A Gate controls the maximum number of concurrently running and waiting queries.
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type Gate struct {
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ch chan struct{}
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}
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// New returns a query gate that limits the number of queries
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// being concurrently executed.
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func New(length int) *Gate {
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return &Gate{
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ch: make(chan struct{}, length),
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}
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}
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// Start blocks until the gate has a free spot or the context is done.
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func (g *Gate) Start(ctx context.Context) error {
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select {
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case <-ctx.Done():
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return ctx.Err()
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case g.ch <- struct{}{}:
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return nil
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}
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}
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// Done releases a single spot in the gate.
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func (g *Gate) Done() {
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select {
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case <-g.ch:
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default:
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panic("gate.Done: more operations done than started")
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}
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}
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