A Golang lock-free thread-safe HashMap optimized for fastest read access.
It requires Golang 1.19+ as it makes use of Generics and the new atomic package helpers.
Warning: This library and derived work is experimental and should not be used in production. It contains an unfixed bug that can cause writes to be lost.
Only Go comparable types are supported as keys.
Set a value for a key in the map:
m := New[string, int]() m.Set("amount", 123)
Read a value for a key from the map:
value, ok := m.Get("amount")
Use the map to count URL requests:
m := New[string, *int64]() var i int64 counter, _ := m.GetOrInsert("api/123", &i) atomic.AddInt64(counter, 1) // increase counter ... count := atomic.LoadInt64(counter) // read counter
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
BenchmarkReadHashMapUint-8 2534198 480.4 ns/op BenchmarkReadHaxMapUint-8 2350569 523.0 ns/op BenchmarkReadGoMapUintUnsafe-8 3308552 367.4 ns/op BenchmarkReadGoMapUintMutex-8 85701 13820 ns/op BenchmarkReadGoSyncMapUint-8 981177 1234 ns/op
Reading from the map while writes are happening:
BenchmarkReadHashMapWithWritesUint-8 1852483 646.7 ns/op BenchmarkReadHaxMapWithWritesUint-8 1761938 680.3 ns/op BenchmarkReadGoSyncMapWithWritesUint-8 758544 1512 ns/op
Write performance without any concurrent reads:
BenchmarkWriteHashMapUint-8 30304 42174 ns/op BenchmarkWriteGoMapMutexUint-8 174100 7223 ns/op BenchmarkWriteGoSyncMapUint-8 24432 45512 ns/op
The benchmarks were run with Golang 1.19.0 on Linux using
Benefits over Golang's builtin map
thread-safe access without need of a(n extra) mutex
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 The library limits the index into the slice, therefore the Golang size check is obsolete.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.