[](#hashmap----)hashmap

[](#overview)Overview

A Golang lock-free thread-safe HashMap optimized for fastest read access.

[](#usage)Usage

Set a value for a key in the map:

m := &HashMap{}
m.Set("amount", 123)

Read a value for a key from the map:

amount, ok := m.Get("amount")

Use the map to count URL requests:

var i int64
actual, _ := m.GetOrInsert("api/123", &i)
counter := (actual).(*int64)
atomic.AddInt64(counter, 1) // increase counter
...
count := atomic.LoadInt64(counter) // read counter

[](#benchmarks)Benchmarks

Reading from the hash map in a thread-safe way is nearly as fast as reading from a standard Golang map in an unsafe way and twice as fast as Go's sync.Map:

BenchmarkReadHashMapUint-8 200000 6830 ns/op
BenchmarkReadGoMapUintUnsafe-8 300000 4280 ns/op
BenchmarkReadGoMapUintMutex-8 30000 51294 ns/op
BenchmarkReadGoSyncMapUint-8 200000 10351 ns/op

If your keys for the map are already hashes, no extra hashing needs to be done by the map:

BenchmarkReadHashMapHashedKey-8 1000000 1692 ns/op

Reading from the map while writes are happening:

BenchmarkReadHashMapWithWritesUint-8 200000 8395 ns/op
BenchmarkReadGoMapWithWritesUintMutex-8 10000 143793 ns/op
BenchmarkReadGoSyncMapWithWritesUint-8 100000 12221 ns/op

Write performance without any concurrent reads:

BenchmarkWriteHashMapUint-8 10000 210383 ns/op
BenchmarkWriteGoMapMutexUint-8 30000 53331 ns/op
BenchmarkWriteGoSyncMapUint-8 10000 176903 ns/op

The benchmarks were run with Golang 1.10.1 on MacOS.

[](#benefits-over-golangs-builtin-map)Benefits over Golangs builtin map

Faster
thread-safe access without need of a(n extra) mutex
Compare-and-swap access for values
Access functions for keys that are hashes and do not need to be hashed again

[](#benefits-over-golangs-syncmap)Benefits over Golangs sync.Map

Faster
Access functions for keys that are hashes and do not need to be hashed again

[](#technical-details)Technical details

Technical design decisions have been made based on benchmarks that are stored in an external repository: go-benchmark
The library uses a sorted doubly linked list and a slice as an index into that list.
The Get() function contains helper functions that have been inlined manually until the Golang compiler will inline them automatically.
It optimizes the slice access by circumventing the Golang size check when reading from the slice. Once a slice is allocated, the size of it does not change. The library limits the index into the slice, therefore the Golang size check is obsolete. When the slice reaches a defined fill rate, a bigger slice is allocated and all keys are recalculated and transferred into the new slice.

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创建于: 2022-08-23 15:31:21
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