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Implement Update method #134

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24 changes: 24 additions & 0 deletions concurrent_map.go
Original file line number Diff line number Diff line change
Expand Up @@ -75,6 +75,30 @@ func (m ConcurrentMap[K, V]) Set(key K, value V) {
shard.Unlock()
}

// Callback to update an element in the map.
// If the element doesn't exist in the map, the parameter will receive the zero value for the value type.
// The returned value will be stored in the map replacing the existing value.
// Returning false for the second return value aborts the update.
// It is called while lock is held, therefore it MUST NOT
// try to access other keys in same map, as it can lead to deadlock since
// Go sync.RWLock is not reentrant
type UpdateCb[V any] func(exist bool, valueInMap V) (V, bool)

// Update an existing element using UpdateCb, assuming the key exists.
// If it does not, the zero value for the value type is passed to the callback.
// if the callback return false for the second return value, the map will not be updated.
func (m ConcurrentMap[K, V]) Update(key K, cb UpdateCb[V]) (res V) {

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Suggested change
func (m ConcurrentMap[K, V]) Update(key K, cb UpdateCb[V]) (res V) {
func (m ConcurrentMap[K, V]) Update(key K, cb UpdateCb[V]) (res V, ok bool) {

shard := m.GetShard(key)
shard.Lock()
v, ok := shard.items[key]
res, update := cb(ok, v)
if update {
shard.items[key] = res
}
shard.Unlock()
return res
}

// Callback to return new element to be inserted into the map
// It is called while lock is held, therefore it MUST NOT
// try to access other keys in same map, as it can lead to deadlock since
Expand Down
62 changes: 62 additions & 0 deletions concurrent_map_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -479,6 +479,68 @@ func TestFnv32(t *testing.T) {

}

func TestUpdate(t *testing.T) {
m := New[Animal]()
lion := Animal{"lion"}

m.Set("safari", lion)
m.Update("safari", func(exists bool, valueInMap Animal) (Animal, bool) {
if !exists {
t.Error("Update recieved false exists flag for existing key")
}
valueInMap.name = "tiger"
return valueInMap, true
})
safari, ok := m.Get("safari")
if safari.name != "tiger" || !ok {
t.Error("Set, then Update failed")
}

m.Update("marine", func(exists bool, valueInMap Animal) (Animal, bool) {
if exists {
t.Error("Update recieved exists flag for empty key")
}
if valueInMap.name != "" {
t.Error("Update did not receive zero value for non existing key")
}
valueInMap.name = "whale"
return valueInMap, true
})
marineAnimals, ok := m.Get("marine")
if marineAnimals.name != "whale" || !ok {
t.Error("Update on non-existing key failed")
}

// return false to prevent updateing map
m.Set("safari", lion)
m.Update("safari", func(exists bool, valueInMap Animal) (Animal, bool) {
if !exists {
t.Error("Update recieved false exists flag for existing key")
}
valueInMap.name = "tiger"
return valueInMap, false
})
safari, ok = m.Get("safari")
if safari.name != "lion" || !ok {
t.Error("Set, then aborting Update failed")
}

m.Update("tundra", func(exists bool, valueInMap Animal) (Animal, bool) {
if exists {
t.Error("Update recieved exists flag for empty key")
}
if valueInMap.name != "" {
t.Error("Update did not receive zero value for non existing key")
}
valueInMap.name = "moose"
return valueInMap, false
})
_, ok = m.Get("tundra")
if ok {
t.Error("Update aborting on non-existing key failed")
}
}

func TestUpsert(t *testing.T) {
dolphin := Animal{"dolphin"}
whale := Animal{"whale"}
Expand Down