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48 lines
1.3 KiB
48 lines
1.3 KiB
// 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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