pmaps

Documentation

Overview

Package pmaps provides an unordered, thread-safe, RWMutex-mechanic map pmaps.RWMap.

Index

• func GoMapSize[K comparable, V any](m map[K]V) (size uint64)
• func NewRWMap[K comparable, V any]() (rwMap parli.ThreadSafeMap[K, V])
• type RWMap
  • func NewRWMap2[K comparable, V any]() (rwMap *RWMap[K, V])
  • func (m *RWMap) Clear(useRange ...bool)
  • func (m *RWMap[K, V]) Clone() (clone parli.ThreadSafeMap[K, V])
  • func (m *RWMap[K, V]) Clone2() (clone *RWMap[K, V])
  • func (m *RWMap) Delete(key K, useZeroValue ...bool)
  • func (m *RWMap) Get(key K) (value V, ok bool)
  • func (m *RWMap) GetOrCreate(key K, newV func() (value *V), makeV func() (value V)) (value V, hasValue bool)
  • func (m *RWMap[K, V]) Keys(n ...int) (keys []K)
  • func (m *RWMap) Length() (length int)
  • func (m *RWMap) List(n ...int) (list []V)
  • func (m *RWMap) Put(key K, value V)
  • func (m *RWMap[K, V]) PutIf(key K, value V, putIf func(value V) (doPut bool)) (wasNewKey bool)
  • func (m *RWMap) Range(rangeFunc func(key K, value V) (keepGoing bool)) (rangedAll bool)

Functions

func GoMapSize

func GoMapSize[K comparable, V any](m map[K]V) (size uint64)

GoMapSize returns the current size of the bucket array of Go map m

• size is 0 for a nil map
• size is 1 for an unallocated hash-table — rare case
• otherwise size is a power of 2

About Go map:

• Go map is a hash map
• a hash table is a space-time trade-off compared to array access
• size is how many slots m’s hash table currently has
• size may grow or shrink as m is modified
• a mapping of the hash value-space is used for hash-table array access
• each map slot contains a linked list of key-value pairs
• more slots is faster closing in on O(1) complexity, fewer slots saves memory
• Load factor is number of hash-table entries including collisions divided by hash table size

Source code:

• the map source code part of the runtime package is available online:
• — https://go.googlesource.com/go/+/refs/heads/master/src/runtime/map.go
• runtime source is typically installed on a computer that has Go:
• — module directory: …libexec/src, package directory: runtime
• — on macOS homebrew similar to: …/homebrew/Cellar/go/1.20.2/libexec/src

func NewRWMap

func NewRWMap[K comparable, V any]() (rwMap parli.ThreadSafeMap[K, V])

NewRWMap returns a thread-safe map implementation

Types

type RWMap

type RWMap[K comparable, V any] struct {
	// contains filtered or unexported fields
}

RWMap is a thread-safe mapping based on read/write mutex

• 5 native Go map functions: Get Put Delete Length Range
• — Delete optionally writes zero-value
• complex atomic methods:
• — GetOrCreate method is an atomic, thread-safe operation as opposed to Get-then-Put
• — PutIf is atomic, thread-safe operation
• convenience methods:
• — Clone Clone2 based on maps.Clone
• — Clear using fast recreate or maps.Range optionally writing zero-values
• order functions:
• — List unordered values
• — Keys unordered keys
• V is copied so if V is large or contains locks, use pointer to V type
• RWMap implements parli.ThreadSafeMap[K comparable, V any]
• —
• map mechanic is Go map
• RWMap uses reader/writer mutual exclusion lock for slightly higher performance
• Get methods are O(1)
• innermost type provides thread-safety
• outermost type provides map api

func NewRWMap2

func NewRWMap2[K comparable, V any]() (rwMap *RWMap[K, V])

NewRWMap2 returns a thread-safe map implementation

func (*RWMap) Clear

func (m *RWMap) Clear(useRange ...bool)

Clear empties the map

func (*RWMap[K, V]) Clone

func (m *RWMap[K, V]) Clone() (clone parli.ThreadSafeMap[K, V])

Clone returns a shallow clone of the map

func (*RWMap[K, V]) Clone2

func (m *RWMap[K, V]) Clone2() (clone *RWMap[K, V])

Clone returns a shallow clone of the map

func (*RWMap) Delete

func (m *RWMap) Delete(key K, useZeroValue ...bool)

func (*RWMap) Get

func (m *RWMap) Get(key K) (value V, ok bool)

func (*RWMap) GetOrCreate

func (m *RWMap) GetOrCreate(
	key K,
	newV func() (value *V),
	makeV func() (value V),
) (value V, hasValue bool)

GetOrCreate returns an item from the map if it exists otherwise creates it.

• newV or makeV are invoked in the critical section, ie. these functions may not access the map or deadlock
• if a key is mapped, its value is returned
• otherwise, if newV and makeV are both nil, nil is returned.
• otherwise, if newV is present, it is invoked to return a pointer ot a value. A nil return value from newV causes panic. A new mapping is created using the value pointed to by the newV return value.
• otherwise, a mapping is created using whatever makeV returns
• newV and makeV may not access the map. The map’s write lock is held during their execution
• GetOrCreate is an atomic, thread-safe operation
• value insert is O(log n)

func (*RWMap[K, V]) Keys

func (m *RWMap[K, V]) Keys(n ...int) (keys []K)

Keys provides the mapping keys, undefined ordering

• O(n)
• invoked while holding RLock or Lock

func (*RWMap) Length

func (m *RWMap) Length() (length int)

func (*RWMap) List

func (m *RWMap) List(n ...int) (list []V)

List provides the mapped values, undefined ordering

• O(n)

func (*RWMap) Put

func (m *RWMap) Put(key K, value V)

func (*RWMap[K, V]) PutIf

func (m *RWMap[K, V]) PutIf(key K, value V, putIf func(value V) (doPut bool)) (wasNewKey bool)

Putif is conditional Put depending on the return value from the putIf function

• if key does not exist in the map, the put is carried out and wasNewKey is true
• if key exists and putIf is nil or returns true, the put is carried out and wasNewKey is false
• if key exists and putIf returns false, the put is not carried out and wasNewKey is false
• during PutIf, the map cannot be accessed and the map’s write-lock is held
• PutIf is an atomic, thread-safe operation

func (*RWMap) Range

func (m *RWMap) Range(rangeFunc func(key K, value V) (keepGoing bool)) (rangedAll bool)