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# Designing an Idiomatic API Interface
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We (the maintainers) built `go-cuckoo`'s API interface without design intent.
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Up until now, we paid more attention implementing the underlying functionality of the cuckoo hashing.
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With the fundamentals of the algorithm built, we should revisit the interface.
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It should align closer to the following principles:
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- **Congruency**
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A `go-cuckoo` table should have the same core functionality as Go's built-in map.
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- **Familiarity**
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A `go-cuckoo` table should behave similarly to Go's standard map, so users will intuitively know how to use it.
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In effect, its users will carry less cognitive load.
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## Current State
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### Interface of the built-in Map
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Listed below is every interface provided by Go to the built-in map object.
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Also included, are the functions from the package `maps` in the standard library.
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<details>
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<summary>Interfaces</summary>
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| # | built-in Interface | Description |
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| --- | ---------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------- |
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| 1 | `m := make(map[K]V)` | Returns an empty map using the built-in `make()` function. |
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| 2 | `m := make(map[K]V, hint)` | Returns an empty map using `make()`, with a capacity 'hint'. This hint is how many items the map expects to hold, _not_ a measure of how large it is. |
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| 3 | `m := map[K]V{...}` | Returns a map, which may be filled with entries in the ellipsis (optional). |
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| 4 | `var m map[K]V` | Defines an empty _variable_ that holds a map. This differs from #1 because `m` is uninitialized (nil) here. |
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| 5 | `m[k] := v` | Assigns the value of `k` to `v`. |
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| 6 | `v := m[k]` | Returns the value of `k` if it exists. Otherwise, `v` is uninitialized. |
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| 7 | `v, ok := m[k]` | Similar to #6, except `ok` is equal to whether `v` is initialized. This is comma-ok notation. |
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| 8 | `for k, v := range m` | Iterates over every key-value pair in `m`. The order is random. |
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| 9 | `delete(m, k)` | Unassigns the value `k`. Returns no value. |
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| 10 | `clear(m)` | Unassigns all keys in `m`. Returns no value. |
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| 11 | `n := len(m)` | Returns the number of entries in `m`. If nil, `m` returns 0. |
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| 12 | `m2 := maps.Clone(m)` | Returns a copy of `m`. |
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| 13 | `maps.Copy(dst, src)` | Assigns every entry of `src` in `dst`. |
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| 14 | `ok := maps.Equal(m1, m2)` | Returns true iff `m1` and `m2` the same entries. |
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| 15 | `ok := maps.EqualFunc(m1, m2, fn)` | Like #14, but with a custom comparator for non-comparable values. |
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| 16 | `maps.DeleteFunc(m, fn)` | Removes every entry in `m` which satisfies `fn`. Returns no value. |
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| 17 | `it2 := maps.All(m)` | Returns an 2D iterator over every key-value pair. |
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| 18 | `it := maps.Keys(m)` | Returns an iterator over every key. |
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| 19 | `it := maps.Values(m)` | Returns an iterator over every value. There can be duplicates. |
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| 20 | `m := maps.Collect(seq)` | Returns a map, with every entry defined in a 2D iterator over key-value pairs. |
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| 21 | `maps.Insert(m, seq)` | Assigns to `m` all key-value pairs in 2D iterator `seq`. Returns no value. |
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</details>
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### Interface of `go-cuckoo`
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On the other hand, here is the current contract for `go-cuckoo`.
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<details>
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<summary>Interfaces</summary>
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| # | built-in Interface | Description |
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| --- | -------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------- |
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| 1 | `m := New(opts...)` | Creates a table using the default hash and equal function. The options configure its behavior. Confined to comparable keys. |
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| 2 | `m := NewBy(keyFunc, opts...)` | Like #1, but allows any key type. A `keyFunc` is used to derive a comparable key. |
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| 3 | `m := NewCustom(hashA, hashB, equalFunc, opts...)` | Like #1, but allows control over the hashes used to allow any key type. An `equalFunc` determines key equality. |
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| 4 | `seq := m.Entries()` | Returns an unordered 2D iterator of all key-value pairs in the table. |
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| 5 | `v := m.Find(k)` | Removes the value for `k`. Returns true if `k` existed. |
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| 6 | `v, ok := m.Get(k)` | Returns the value for `k` in the table. Also, returns true if the `k` exists, otherwise false. When false, `v` is undefined. |
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| 7 | `ok := m.Has(k)` | Returns true if `k` is in the table. |
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| 8 | `err := m.Put(k, v)` | Sets value `v` for key `k`. Otherwise, returns error. |
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| 9 | `n := m.Size()` | Returns the number of items in `m`. |
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| 10 | `str := m.String()` | Returns `m` as a string in the format "table[k1:v1 k2:v2 ...]". |
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| 11 | `cap := m.TotalCapacity()` | Returns how many slots `m` has allocated. |
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| 12 | `ok := m.Drop(k)` | Removes `k` from the table. Returns whether the key had existed. |
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</details>
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### Determining Congruency
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So, how does the core functionality compare?
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Listed below is an analysis of every interface in Go's standard map.
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Each is compared against what `go-cuckoo` offers, and categorized into the following groups:
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- ✅ Covered: an analog exists.
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- ⚠️ Partial: workaround available.
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- ❌ Gap: no analog yet; addressed in [Target State](#solving-congruency).
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Specifically, here we are checking for functionality.
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Is there functionality that this offers which `go-cuckoo` does not?
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We are checking accessibility, but not discoverability.
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The latter will be considered later.
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<details>
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<summary>✅ <code>m := make(map[K]V)</code></summary>
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The analog is `m := New()`.
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</details>
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<details>
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<summary>⚠️ <code>m := make(map[K]V, hint)</code></summary>
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This has no simple analog.
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It is close to `m := New(Capacity(hint))`, but it assigns starting capacity, not expected size.
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For the built-in map, these are two separate things.
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- Capacity is an internal measure, used to optimize space/speed.
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It is hidden from the user because it depends on the underlying implementation, which may change.
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- Expected size requires the map must hold a number of items before resizing.
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This is tangeable and agnostic to implementation, hence why it is given to the user.
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In short, this interface defines expected size, but `Capacity()` defines capacity.
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</details>
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<details>
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<summary>❌ <code>m := map[K]V{...}</code></summary>
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This has no simple analog, the closest being:
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```go
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m := New[K, V]()
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for k, v := range startingEntries {
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m.Put(k, v)
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}
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```
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It is idiomatic, but far less ergonomic.
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</details>
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<details>
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<summary>✅ <code>var m map[K]V</code></summary>
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The analog is `var m Table[K, V]`.
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</details>
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<details>
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<summary>✅ <code>m[k] := v</code></summary>
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The analog is `err := m.Put(k, v)`.
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</details>
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<details>
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<summary>✅ <code>v := m[k]</code></summary>
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The analog is `v := m.Find(k)`.
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</details>
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<details>
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<summary>✅ <code>v, ok := m[k]</code></summary>
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The analog is `v, ok := m.Get(k)`.
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</details>
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<details>
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<summary>✅ <code>for k, v := range m</code></summary>
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The analog is `for k, v := range m.Entries()`.
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</details>
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<details>
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<summary>✅ <code>delete(m, k)</code></summary>
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The analog is `ok := m.Drop(k)`.
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</details>
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<details>
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<summary>❌ <code>clear(m)</code></summary>
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There is no analog.
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The easiest may to do this is to delete all items individually:
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```go
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for k := range m.Entries() {
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m.Drop(k)
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}
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```
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</details>
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<details>
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<summary>✅ <code>n := len(m)</code></summary>
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The analog is `n := m.Size()`.
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</details>
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<details>
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<summary>❌ <code>m2 := maps.Clone(m)</code></summary>
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There is no analog.
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The easiest way to do this currently is to make a new map, and manually add the items.
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```go
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m2 := cuckoo.Table[K, V]()
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for k, v := range m.Entries() {
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m2.Put(k, v)
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}
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```
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This gets complicated by the various options available to the user.
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Furthermore, any custom `EqualFunc`, `keyFunc` or `Hash` is not transferred.
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</details>
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<details>
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<summary>❌ <code>maps.Copy(dst, src)</code></summary>
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There is no analog.
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The simplest way to do this is with a for-loop.
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```go
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for k, v := range src.Entries() {
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dst.Put(k, v)
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}
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```
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</details>
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<details>
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<summary>❌ <code>ok := maps.Equal(m1, m2)</code></summary>
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There is no analog.
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Users have to manually check the key-value pairs to determine equality.
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</details>
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<details>
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<summary>❌ <code>ok := maps.EqualFunc(m1, m2, fn)</code></summary>
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There is no analog.
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Users have to manually check the key-value pairs to determine equality.
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</details>
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<details>
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<summary>❌ <code>maps.DeleteFunc(m, fn)</code></summary>
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There is no analog.
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Users have to manually delete keys.
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</details>
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<details>
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<summary>✅ <code>it2 := maps.All(m)</code></summary>
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The analog is `it2 := m.Entries()`.
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</details>
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<details>
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<summary>⚠️ <code>it := maps.Keys(m)</code></summary>
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There is no simple analog.
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A close neighbor is `it2 := m.Entries()`.
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Users can use this in a for-loop, and pick out just the keys:
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```go
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for k := range m.Entries() {
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// ...
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}
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```
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</details>
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<details>
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<summary>⚠️ <code>it := maps.Values(m)</code></summary>
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There is no simple analog.
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A close neighbor is `it2 := m.Entries()`.
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Users can use this in a for-loop, and pick out just the values:
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```go
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for _, v := range m.Entries() {
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// ...
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}
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```
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</details>
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<details>
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<summary>❌ <code>m := maps.Collect(seq)</code></summary>
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There is no analog.
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</details>
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<details>
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<summary>❌ <code>maps.Insert(m, seq)</code></summary>
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There is no analog.
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</details>
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## Target State
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### Solving Congruency
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We should make the following changes to accomodate for congruency:
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<details>
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<summary><code>ok := maps.EqualFunc(m1, m2, fn)</code></summary>
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We should implement a new function:
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```go
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func EqualFunc[K, V1, V2 any](t1 *Table[K, V1], t2 *Table[K, V2], eq func(V1, V2) bool) bool
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```
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This function is free, and not bound as a receiver function.
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(It is called `cuckoo.Equal(t1, t2)`, not `t1.Equals(t2)`.)
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The latter implies `t1` has authority, when in fact neither do.
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We define equality as:
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1. Neither table has a key the other doesn't.
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2. Each key has the same value in each table.
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Parameter `eq` determines this equality.
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Custom `EqualFunc`'s complicate this, as they modulate key identity in tables.
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If two tables may differ on whether two keys are different, this function might break.
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So, we must assume that:
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- Both tables have `EqualFunc`'s which 'agree' on the identity of the keys present in the tables.
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Agreement is defined as: if two keys are distinct in one table, they are distinct in the other.
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The name `EqualFunc` is already taken by `EqualFunc[K, V]`: an alias for `func(a, b K) bool`.
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Inlining `EqualFunc[K, V]` would solve this problem.
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We will move the documentation attached to it to `DefaultEqualFunc`.
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|
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</details>
|
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|
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<details>
|
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<summary><code>ok := maps.Equal(m1, m2)</code></summary>
|
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|
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We should implement a new function, to conform with the standard library:
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```go
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func Equal[K any, V comparable](t1, t2 *Table[K, V]) bool
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```
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It uses the same equality check as in `EqualFunc`.
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Once again, the function is free because it is symmetric.
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</details>
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|
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<details>
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<summary><code>maps.Insert(m, seq)</code></summary>
|
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|
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We should implement a new receiver for the table:
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|
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```go
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func (t *Table[K, V]) Insert(seq iter.Seq2[K, V]) error
|
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```
|
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|
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A receiver fits better even though `maps.Insert` is a free function, because copying it is asymmetric.
|
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Map `dst` receives entries from map `src`.
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It's only free because Go's standard map is built into the language, and so cannot have receivers.
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|
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In terms of naming, `t.Extend` is more accurate, and has precedent in [Python](docs.python.org/3/tutorial/datastructures.html#more-on-lists) and [Rust](https://doc.rust-lang.org/std/iter/trait.Extend.html).
|
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When [adding iterator function](https://github.com/golang/go/issues/61900) to the `maps` package, the Go team chose to frame it as 'sources' and 'sinks'.
|
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With this model, `maps.Insert` made more sense than `maps.Extend`.
|
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Ultimately, `t.Insert()` is a better choice to be consistent with `maps`.
|
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|
||||
</details>
|
||||
|
||||
<details>
|
||||
<summary><code>maps.Copy(dst, src)</code></summary>
|
||||
|
||||
We should implement a new receiver for the table:
|
||||
|
||||
```go
|
||||
func (t *Table[K, V]) Copy(src *Table[K, V]) error
|
||||
```
|
||||
|
||||
It's functionality should match that of `t.Insert()`.
|
||||
|
||||
A receiver fits better even though `maps.Copy` is a free function, 'copying' it is asymmetric: `dst` is writen into by `src`.
|
||||
It is only free because Go's standard map is built into the language, and so cannot have receivers.
|
||||
|
||||
The name `t.Merge()` might be more accurate, but it does work because:
|
||||
|
||||
- `t.Copy()` matches Go's built-in `copy()`, and `io.Copy()`. The Go team used [the same logic](https://github.com/golang/go/discussions/47330#discussioncomment-1167799) to name `maps.Copy()`.
|
||||
In this case, `t.Merge()` would be an outlier.
|
||||
- `t.Merge()` implies some sort of conflict-resolution, when there is not.
|
||||
It simply overwrites the values.
|
||||
|
||||
</details>
|
||||
|
||||
<details>
|
||||
<summary><code>maps.DeleteFunc(m, fn)</code></summary>
|
||||
|
||||
We should implement a new receiver for the table:
|
||||
|
||||
```go
|
||||
func (t *Table[K, V]) DeleteFunc(del func(K, V) bool)
|
||||
```
|
||||
|
||||
It would have the same functionality as `maps.DeleteFunc`.
|
||||
|
||||
A free function could work here, but `t` has clear authority over `del`.
|
||||
Other than being consistent with the `maps` package, `t.DeleteFunc` follows the Go convention of appending `Func` to higher-order equivalents of functions.
|
||||
This trumps names like `t.DeleteIf`, which lend more to [Java](https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#removeIf-java.util.function.Predicate-) or [C++](https://en.cppreference.com/cpp/algorithm/remove).
|
||||
The word `Delete` is also convention, tying back to the built-in `delete()`.
|
||||
|
||||
</details>
|
||||
|
||||
<details>
|
||||
<summary><code>m := maps.Collect(seq)</code></summary>
|
||||
|
||||
We should implement a new constructor.
|
||||
|
||||
```go
|
||||
func Collect[K comparable, V any](seq iter.Seq2[K, V]) (*Table[K, V], error)
|
||||
```
|
||||
|
||||
It would create a `New()` table, and insert all entries in `seq`.
|
||||
|
||||
This reveicer only supports the standard table constructor, with comparable keys.
|
||||
It is tempting to add `CollectBy` or `CollectCustom` to support all table types, but doing so would pollute the public interface.
|
||||
|
||||
It would be just one more line to initialize the table and then call `t.Insert` directly:
|
||||
|
||||
```go
|
||||
t := // ...
|
||||
err := t.Insert(seq)
|
||||
```
|
||||
|
||||
</details>
|
||||
|
||||
<details>
|
||||
<summary><code>m := map[K]V{...}</code></summary>
|
||||
|
||||
We should make a new constructor, because entries are generic.
|
||||
So, creating an option with inialized entries doesn't work.
|
||||
|
||||
With the previous additions, users have a few options.
|
||||
If they want to use a `New()` table, `t.Collect` matches well:
|
||||
|
||||
```go
|
||||
t, err := cuckoo.Collect(func(yield func(K, V) bool) {
|
||||
yield(key1, val1)
|
||||
yield(key2, val2)
|
||||
})
|
||||
```
|
||||
|
||||
For `NewCustom()` or `NewBy()` tables, users can call `t.Insert` after initialization:
|
||||
|
||||
```go
|
||||
t := // ...
|
||||
err := t.Insert(func(yield func(K, V) bool) {
|
||||
yield(key1, val1)
|
||||
yield(key2, val2)
|
||||
})
|
||||
```
|
||||
|
||||
It is one more line.
|
||||
But, the alternative is polluting the public interface with corresponding `*WithEntries` constuctors.
|
||||
|
||||
</details>
|
||||
|
||||
<details>
|
||||
<summary><code>m := make(map[K]V, hint)</code></summary>
|
||||
|
||||
We should add a new option:
|
||||
|
||||
```go
|
||||
func ExpectedSize(n int) Option
|
||||
```
|
||||
|
||||
When fed to a table, it will allocate enough space to hold `n` entries without a resize.
|
||||
|
||||
</details>
|
||||
|
||||
<details>
|
||||
<summary><code>clear(m)</code></summary>
|
||||
|
||||
We should implement a new receiver:
|
||||
|
||||
```go
|
||||
func (t *Table[K, V]) Clear()
|
||||
```
|
||||
|
||||
It will remove all entries from the table.
|
||||
|
||||
</details>
|
||||
|
||||
<details>
|
||||
<summary><code>m2 := maps.Clone(m)</code></summary>
|
||||
|
||||
We should implement a matching function:
|
||||
|
||||
```go
|
||||
func (t *Table[K, V]) Clone() *Table[K, V]
|
||||
```
|
||||
|
||||
Also, it will copy the hash, equality function, and options used in the table.
|
||||
|
||||
</details>
|
||||
|
||||
<details>
|
||||
<summary><code>it := maps.Keys(m)</code></summary>
|
||||
|
||||
We should implement a matching function:
|
||||
|
||||
```go
|
||||
func (t *Table[K, V]) Keys() iter.Seq[K]
|
||||
```
|
||||
|
||||
It is tempting to just have `All()`, but it returns a `Seq2`, not a `Seq`.
|
||||
There is no iterator adaptor between `Seq` and `Seq2`, and will not be for the foreseeable future.
|
||||
This function, while it feels superfluous, is required.
|
||||
|
||||
</details>
|
||||
|
||||
<details>
|
||||
<summary><code>it := maps.Values(m)</code></summary>
|
||||
|
||||
We should implement a matching function:
|
||||
|
||||
```go
|
||||
func (t *Table[K, V]) Values() iter.Seq[V]
|
||||
```
|
||||
|
||||
For the same reason we need `Keys()`, we also need `Values()`.
|
||||
|
||||
</details>
|
||||
@@ -68,13 +68,12 @@ func FuzzInsertLookup(f *testing.F) {
|
||||
|
||||
for _, step := range scenario.steps {
|
||||
if step.drop {
|
||||
ok := actual.Drop(step.key)
|
||||
_, has := expected[step.key]
|
||||
assert.Equal(ok, has)
|
||||
err := actual.Drop(step.key)
|
||||
assert.NoError(err)
|
||||
|
||||
delete(expected, step.key)
|
||||
|
||||
_, ok = actual.Get(step.key)
|
||||
_, ok := actual.Get(step.key)
|
||||
assert.False(ok)
|
||||
} else {
|
||||
err := actual.Put(step.key, step.value)
|
||||
|
||||
@@ -124,9 +124,9 @@ func TestDropExistingItem(t *testing.T) {
|
||||
table := cuckoo.New[int, bool]()
|
||||
(table.Put(key, value))
|
||||
|
||||
had := table.Drop(key)
|
||||
err := table.Drop(key)
|
||||
|
||||
assert.True(had)
|
||||
assert.NoError(err)
|
||||
assert.Equal(0, table.Size())
|
||||
assert.False(table.Has(key))
|
||||
}
|
||||
@@ -136,9 +136,9 @@ func TestDropNoItem(t *testing.T) {
|
||||
key := 0
|
||||
table := cuckoo.New[int, bool]()
|
||||
|
||||
had := table.Drop(key)
|
||||
err := table.Drop(key)
|
||||
|
||||
assert.False(had)
|
||||
assert.NoError(err)
|
||||
assert.Equal(0, table.Size())
|
||||
assert.False(table.Has(key))
|
||||
}
|
||||
@@ -152,9 +152,10 @@ func TestDropItemCapacity(t *testing.T) {
|
||||
)
|
||||
|
||||
startingCapacity := table.TotalCapacity()
|
||||
table.Drop(key)
|
||||
err := table.Drop(key)
|
||||
endingCapacity := table.TotalCapacity()
|
||||
|
||||
assert.NoError(err)
|
||||
assert.Equal(0, table.Size())
|
||||
assert.Equal(uint64(128), startingCapacity)
|
||||
assert.Equal(uint64(64), endingCapacity)
|
||||
@@ -202,9 +203,9 @@ func TestDropResizeCapacity(t *testing.T) {
|
||||
|
||||
err1 := table.Put(0, true)
|
||||
err2 := table.Put(1, true)
|
||||
table.Drop(1)
|
||||
err3 := table.Drop(1)
|
||||
|
||||
assert.NoError(errors.Join(err1, err2))
|
||||
assert.NoError(errors.Join(err1, err2, err3))
|
||||
assert.Equal(uint64(20), table.TotalCapacity())
|
||||
}
|
||||
|
||||
|
||||
3
doc.go
3
doc.go
@@ -5,8 +5,5 @@
|
||||
// a table with any key type using [NewCustom]. Custom [Hash] functions and
|
||||
// key comparison are also supported.
|
||||
//
|
||||
// NOTE: The [Table] is a look-up structure, and not a source of truth. If
|
||||
// [ErrBadHash] occurs, the data cannot be restored.
|
||||
//
|
||||
// See more: https://en.wikipedia.org/wiki/Cuckoo_hashing
|
||||
package cuckoo
|
||||
|
||||
@@ -19,11 +19,6 @@ const DefaultGrowthFactor uint64 = 2
|
||||
// [libcuckoo]: https://github.com/efficient/libcuckoo/blob/656714705a055df2b7a605eb3c71586d9da1e119/libcuckoo/cuckoohash_config.hh#L21
|
||||
const defaultMinimumLoad float64 = 0.05
|
||||
|
||||
// defaultGrowthLimit is the maximum number of times a [Table] can grow in a
|
||||
// single [Table.Put], before the library infers it will lead to a stack
|
||||
// overflow. The value of '64' was chosen arbirarily.
|
||||
const defaultGrowthLimit uint64 = 64
|
||||
|
||||
type settings struct {
|
||||
growthFactor uint64
|
||||
minLoadFactor float64
|
||||
|
||||
18
subtable.go
18
subtable.go
@@ -1,6 +1,5 @@
|
||||
package cuckoo
|
||||
|
||||
// An entry is a key-value pair.
|
||||
type entry[K, V any] struct {
|
||||
key K
|
||||
value V
|
||||
@@ -49,13 +48,10 @@ func (t *subtable[K, V]) drop(key K) (occupied bool) {
|
||||
return false
|
||||
}
|
||||
|
||||
func (t *subtable[K, V]) resized(capacity uint64) *subtable[K, V] {
|
||||
return &subtable[K, V]{
|
||||
slots: make([]slot[K, V], capacity),
|
||||
capacity: capacity,
|
||||
hash: t.hash,
|
||||
compare: t.compare,
|
||||
}
|
||||
func (t *subtable[K, V]) resize(capacity uint64) {
|
||||
t.slots = make([]slot[K, V], capacity)
|
||||
t.capacity = capacity
|
||||
t.size = 0
|
||||
}
|
||||
|
||||
func (t *subtable[K, V]) update(key K, value V) (updated bool) {
|
||||
@@ -73,7 +69,7 @@ func (t *subtable[K, V]) update(key K, value V) (updated bool) {
|
||||
return false
|
||||
}
|
||||
|
||||
func (t *subtable[K, V]) insert(insertion entry[K, V]) (evicted entry[K, V], eviction bool) {
|
||||
func (t *subtable[K, V]) evict(insertion entry[K, V]) (evicted entry[K, V], eviction bool) {
|
||||
if t.capacity == 0 {
|
||||
return insertion, true
|
||||
}
|
||||
@@ -96,8 +92,8 @@ func (t *subtable[K, V]) insert(insertion entry[K, V]) (evicted entry[K, V], evi
|
||||
return insertion, true
|
||||
}
|
||||
|
||||
func newSubtable[K, V any](capacity uint64, hash Hash[K], compare EqualFunc[K]) *subtable[K, V] {
|
||||
return &subtable[K, V]{
|
||||
func newSubtable[K, V any](capacity uint64, hash Hash[K], compare EqualFunc[K]) subtable[K, V] {
|
||||
return subtable[K, V]{
|
||||
hash: hash,
|
||||
capacity: capacity,
|
||||
compare: compare,
|
||||
|
||||
124
table.go
124
table.go
@@ -9,7 +9,7 @@ import (
|
||||
)
|
||||
|
||||
// ErrBadHash occurs when the hashes given to a [Table] cause too many key
|
||||
// collisions. Discard the old table, rebuild it from your source data, and try:
|
||||
// collisions. Try rebuilding the table using:
|
||||
//
|
||||
// 1. Different hash seeds. Equal seeds produce equal hash functions, which
|
||||
// always cycle.
|
||||
@@ -20,7 +20,7 @@ var ErrBadHash = errors.New("bad hash")
|
||||
// one with [New]. Or if you want more granularity, use [NewBy] or
|
||||
// [NewCustom].
|
||||
type Table[K, V any] struct {
|
||||
tableA, tableB *subtable[K, V]
|
||||
tableA, tableB subtable[K, V]
|
||||
growthFactor uint64
|
||||
minLoadFactor float64
|
||||
}
|
||||
@@ -54,61 +54,30 @@ func (t *Table[K, V]) load() float64 {
|
||||
return float64(t.Size()) / float64(t.TotalCapacity())
|
||||
}
|
||||
|
||||
// insert attempts to put/update an entry in the table, without modifying the
|
||||
// size of the table. Returns a displaced entry and 'homeless = true' if an
|
||||
// entry could not be placed after exhausting evictions.
|
||||
func (t *Table[K, V]) insert(entry entry[K, V]) (displaced entry[K, V], homeless bool) {
|
||||
if t.tableA.update(entry.key, entry.value) {
|
||||
return
|
||||
}
|
||||
|
||||
if t.tableB.update(entry.key, entry.value) {
|
||||
return
|
||||
}
|
||||
|
||||
for range t.maxEvictions() {
|
||||
if entry, homeless = t.tableA.insert(entry); !homeless {
|
||||
return
|
||||
}
|
||||
|
||||
if entry, homeless = t.tableB.insert(entry); !homeless {
|
||||
return
|
||||
}
|
||||
}
|
||||
|
||||
return entry, true
|
||||
}
|
||||
|
||||
// resized creates an empty copy of the table, with a new capacity for each
|
||||
// bucket.
|
||||
func (t *Table[K, V]) resized(capacity uint64) *Table[K, V] {
|
||||
return &Table[K, V]{
|
||||
growthFactor: t.growthFactor,
|
||||
minLoadFactor: t.minLoadFactor,
|
||||
tableA: t.tableA.resized(capacity),
|
||||
tableB: t.tableB.resized(capacity),
|
||||
}
|
||||
}
|
||||
|
||||
// resize creates a new [Table.resized] with 'capacity', inserts all items into
|
||||
// the array, and replaces the current table. It is a helper function for
|
||||
// [Table.grow] and [Table.shrink]; use them instead.
|
||||
func (t *Table[K, V]) resize(capacity uint64) bool {
|
||||
updated := t.resized(capacity)
|
||||
|
||||
// resize clears all tables, changes the sizes of them to a specific capacity,
|
||||
// and fills them back up again. It is a helper function for [Table.grow] and
|
||||
// [Table.shrink]; use them instead.
|
||||
func (t *Table[K, V]) resize(capacity uint64) error {
|
||||
entries := make([]entry[K, V], 0, t.Size())
|
||||
for k, v := range t.Entries() {
|
||||
if _, failed := updated.insert(entry[K, V]{k, v}); failed {
|
||||
return false
|
||||
entries = append(entries, entry[K, V]{k, v})
|
||||
}
|
||||
|
||||
t.tableA.resize(capacity)
|
||||
t.tableB.resize(capacity)
|
||||
|
||||
for _, entry := range entries {
|
||||
if err := t.Put(entry.key, entry.value); err != nil {
|
||||
return err
|
||||
}
|
||||
}
|
||||
|
||||
*t = *updated
|
||||
return true
|
||||
return nil
|
||||
}
|
||||
|
||||
// grow increases the table's capacity by the growth factor. If the
|
||||
// capacity is 0, it increases it to 1.
|
||||
func (t *Table[K, V]) grow() bool {
|
||||
func (t *Table[K, V]) grow() error {
|
||||
var newCapacity uint64
|
||||
|
||||
if t.TotalCapacity() == 0 {
|
||||
@@ -122,7 +91,7 @@ func (t *Table[K, V]) grow() bool {
|
||||
|
||||
// shrink reduces the table's capacity by the growth factor. It may
|
||||
// reduce it down to 0.
|
||||
func (t *Table[K, V]) shrink() bool {
|
||||
func (t *Table[K, V]) shrink() error {
|
||||
return t.resize(t.tableA.capacity / t.growthFactor)
|
||||
}
|
||||
|
||||
@@ -153,48 +122,49 @@ func (t *Table[K, V]) Has(key K) (exists bool) {
|
||||
return
|
||||
}
|
||||
|
||||
// Put sets the value for a key. If it cannot be set, an error is returned.
|
||||
// Put sets the value for a key. Returns error if its value cannot be set.
|
||||
func (t *Table[K, V]) Put(key K, value V) (err error) {
|
||||
var (
|
||||
entry = entry[K, V]{key, value}
|
||||
homeless bool
|
||||
)
|
||||
|
||||
for range defaultGrowthLimit {
|
||||
if entry, homeless = t.insert(entry); !homeless {
|
||||
return
|
||||
if t.tableA.update(key, value) {
|
||||
return nil
|
||||
}
|
||||
|
||||
if t.tableB.update(key, value) {
|
||||
return nil
|
||||
}
|
||||
|
||||
entry, eviction := entry[K, V]{key, value}, false
|
||||
for range t.maxEvictions() {
|
||||
if entry, eviction = t.tableA.evict(entry); !eviction {
|
||||
return nil
|
||||
}
|
||||
|
||||
if entry, eviction = t.tableB.evict(entry); !eviction {
|
||||
return nil
|
||||
}
|
||||
}
|
||||
|
||||
// Both this and the growth limit are necessary: this catches bad hashes
|
||||
// early when the table is sparse, while the latter catches cases where
|
||||
// growing never helps.
|
||||
if t.load() < t.minLoadFactor {
|
||||
return fmt.Errorf("hash functions produced a cycle at load %d/%d: %w", t.Size(), t.TotalCapacity(), ErrBadHash)
|
||||
}
|
||||
|
||||
// It is theoretically possible to have a table with a larger capacity
|
||||
// that is valid. But this chance is astronomically small, so we ignore
|
||||
// it in this implementation.
|
||||
if grew := t.grow(); !grew {
|
||||
return fmt.Errorf("could not redistribute entries into larger table: %w", ErrBadHash)
|
||||
}
|
||||
if err := t.grow(); err != nil {
|
||||
return err
|
||||
}
|
||||
|
||||
return fmt.Errorf("could not place entry after %d resizes: %w", defaultGrowthLimit, ErrBadHash)
|
||||
return t.Put(entry.key, entry.value)
|
||||
}
|
||||
|
||||
// Drop removes a value for a key in the table. Returns whether the key had
|
||||
// existed.
|
||||
func (t *Table[K, V]) Drop(key K) bool {
|
||||
occupied := t.tableA.drop(key) || t.tableB.drop(key)
|
||||
// Drop removes a value for a key in the table. Returns an error if its value
|
||||
// cannot be removed.
|
||||
func (t *Table[K, V]) Drop(key K) (err error) {
|
||||
t.tableA.drop(key)
|
||||
t.tableB.drop(key)
|
||||
|
||||
if t.load() < t.minLoadFactor {
|
||||
// The error is not handled here, because table-shrinking is an internal
|
||||
// optimization.
|
||||
t.shrink()
|
||||
return t.shrink()
|
||||
}
|
||||
|
||||
return occupied
|
||||
return nil
|
||||
}
|
||||
|
||||
// Entries returns an unordered sequence of all key-value pairs in the table.
|
||||
|
||||
Reference in New Issue
Block a user