rwmap

Documentation

Index

• type RWMap
  • func (m *RWMap[K, V]) Clear()
  • func (m *RWMap[K, V]) CompareAndDelete(key K, old V) (deleted bool)
  • func (m *RWMap[K, V]) CompareAndSwap(key K, old, new V) (swapped bool)
  • func (m *RWMap[K, V]) Delete(key K)
  • func (m *RWMap[K, V]) Len() (n int64)
  • func (m *RWMap[K, V]) Load(key K) (value V, ok bool)
  • func (m *RWMap[K, V]) LoadAndDelete(key K) (value V, loaded bool)
  • func (m *RWMap[K, V]) LoadOrStore(key K, value V) (actual V, loaded bool)
  • func (m *RWMap[K, V]) Range(f func(key K, value V) bool)
  • func (m *RWMap[K, V]) Store(key K, value V)
  • func (m *RWMap[K, V]) Swap(key K, value V) (previous V, loaded bool)

Types

type RWMap

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

RWMap is like a Go map[interface{}]interface{} but is safe for concurrent use by multiple goroutines without additional locking or coordination. Loads, stores, and deletes run in amortized constant time.

The RWMap type is specialized. Most code should use a plain Go map instead, with separate locking or coordination, for better type safety and to make it easier to maintain other invariants along with the map content.

The RWMap type is optimized for two common use cases: (1) when the entry for a given key is only ever written once but read many times, as in caches that only grow, or (2) when multiple goroutines read, write, and overwrite entries for disjoint sets of keys. In these two cases, use of a RWMap may significantly reduce lock contention compared to a Go map paired with a separate Mutex or RWMutex.

The zero RWMap is empty and ready for use. A RWMap must not be copied after first use.

In the terminology of the Go memory model, RWMap arranges that a write operation “synchronizes before” any read operation that observes the effect of the write, where read and write operations are defined as follows. Load, LoadAndDelete, LoadOrStore, Swap, CompareAndSwap, and CompareAndDelete are read operations; Delete, LoadAndDelete, Store, and Swap are write operations; LoadOrStore is a write operation when it returns loaded set to false; CompareAndSwap is a write operation when it returns swapped set to true; and CompareAndDelete is a write operation when it returns deleted set to true.

func (*RWMap[K, V]) Clear

func (m *RWMap[K, V]) Clear()

Clear deletes all the entries, resulting in an empty Map.

func (*RWMap[K, V]) CompareAndDelete

func (m *RWMap[K, V]) CompareAndDelete(key K, old V) (deleted bool)

CompareAndDelete deletes the entry for key if its value is equal to old. The old value must be of a comparable type.

If there is no current value for key in the map, CompareAndDelete returns false (even if the old value is the nil interface value).

func (*RWMap[K, V]) CompareAndSwap

func (m *RWMap[K, V]) CompareAndSwap(key K, old, new V) (swapped bool)

CompareAndSwap swaps the old and new values for key if the value stored in the map is equal to old. The old value must be of a comparable type.

func (*RWMap[K, V]) Delete

func (m *RWMap[K, V]) Delete(key K)

Delete deletes the value for a key.

func (*RWMap[K, V]) Len

func (m *RWMap[K, V]) Len() (n int64)

func (*RWMap[K, V]) Load

func (m *RWMap[K, V]) Load(key K) (value V, ok bool)

Load returns the value stored in the map for a key, or nil if no value is present. The ok result indicates whether value was found in the map.

func (*RWMap[K, V]) LoadAndDelete

func (m *RWMap[K, V]) LoadAndDelete(key K) (value V, loaded bool)

LoadAndDelete deletes the value for a key, returning the previous value if any. The loaded result reports whether the key was present.

func (*RWMap[K, V]) LoadOrStore

func (m *RWMap[K, V]) LoadOrStore(key K, value V) (actual V, loaded bool)

LoadOrStore returns the existing value for the key if present. Otherwise, it stores and returns the given value. The loaded result is true if the value was loaded, false if stored.

func (*RWMap[K, V]) Range

func (m *RWMap[K, V]) Range(f func(key K, value V) bool)

Range calls f sequentially for each key and value present in the map. If f returns false, range stops the iteration.

Range does not necessarily correspond to any consistent snapshot of the Map's contents: no key will be visited more than once, but if the value for any key is stored or deleted concurrently (including by f), Range may reflect any mapping for that key from any point during the Range call. Range does not block other methods on the receiver; even f itself may call any method on m.

Range may be O(N) with the number of elements in the map even if f returns false after a constant number of calls.

func (*RWMap[K, V]) Store

func (m *RWMap[K, V]) Store(key K, value V)

Store sets the value for a key.

func (*RWMap[K, V]) Swap

func (m *RWMap[K, V]) Swap(key K, value V) (previous V, loaded bool)

Swap swaps the value for a key and returns the previous value if any. The loaded result reports whether the key was present.