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55 lines
1.5 KiB
Go
55 lines
1.5 KiB
Go
// Copyright The OpenTelemetry Authors
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//
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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 metric // import "go.opentelemetry.io/otel/sdk/metric"
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import (
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"sync"
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)
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// cache is a locking storage used to quickly return already computed values.
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//
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// The zero value of a cache is empty and ready to use.
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//
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// A cache must not be copied after first use.
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//
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// All methods of a cache are safe to call concurrently.
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type cache[K comparable, V any] struct {
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sync.Mutex
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data map[K]V
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}
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// Lookup returns the value stored in the cache with the associated key if it
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// exists. Otherwise, f is called and its returned value is set in the cache
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// for key and returned.
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//
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// Lookup is safe to call concurrently. It will hold the cache lock, so f
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// should not block excessively.
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func (c *cache[K, V]) Lookup(key K, f func() V) V {
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c.Lock()
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defer c.Unlock()
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if c.data == nil {
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val := f()
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c.data = map[K]V{key: val}
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return val
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}
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if v, ok := c.data[key]; ok {
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return v
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}
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val := f()
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c.data[key] = val
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return val
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}
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