Source File
	registry.go

Belonging Package
	github.com/apache/arrow-go/v18/arrow/compute

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//go:build go1.18

package compute

import (
	"maps"
	"slices"
	"sync"

	"github.com/apache/arrow-go/v18/arrow/internal/debug"
)

type FunctionRegistry interface {
	CanAddFunction(fn Function, allowOverwrite bool) bool
	AddFunction(fn Function, allowOverwrite bool) bool
	CanAddAlias(target, source string) bool
	AddAlias(target, source string) bool
	GetFunction(name string) (Function, bool)
	GetFunctionNames() []string
	NumFunctions() int

	canAddFuncName(string, bool) bool
}

var (
	registry FunctionRegistry
	once     sync.Once
)

func GetFunctionRegistry() FunctionRegistry {
	once.Do(func() {
		registry = NewRegistry()
		RegisterScalarCast(registry)
		RegisterVectorSelection(registry)
		RegisterScalarBoolean(registry)
		RegisterScalarArithmetic(registry)
		RegisterScalarComparisons(registry)
		RegisterVectorHash(registry)
		RegisterVectorRunEndFuncs(registry)
		RegisterScalarSetLookup(registry)
	})
	return registry
}

func NewRegistry() FunctionRegistry {
	return &funcRegistry{
		nameToFunction: make(map[string]Function)}
}

func NewChildRegistry(parent FunctionRegistry) FunctionRegistry {
	return &funcRegistry{
		parent:         parent.(*funcRegistry),
		nameToFunction: make(map[string]Function)}
}

type funcRegistry struct {
	parent *funcRegistry

	mx             sync.RWMutex
	nameToFunction map[string]Function
}

func (reg *funcRegistry) getLocker(add bool) sync.Locker {
	if add {
		return &reg.mx
	}
	return reg.mx.RLocker()
}

func (reg *funcRegistry) CanAddFunction(fn Function, allowOverwrite bool) bool {
	if reg.parent != nil && !reg.parent.CanAddFunction(fn, allowOverwrite) {
		return false
	}

	return reg.doAddFunction(fn, allowOverwrite, false)
}

func (reg *funcRegistry) AddFunction(fn Function, allowOverwrite bool) bool {
	if reg.parent != nil && !reg.parent.CanAddFunction(fn, allowOverwrite) {
		return false
	}

	return reg.doAddFunction(fn, allowOverwrite, true)
}

func (reg *funcRegistry) CanAddAlias(target, source string) bool {
	if reg.parent != nil && !reg.parent.canAddFuncName(target, false) {
		return false
	}
	return reg.doAddAlias(target, source, false)
}

func (reg *funcRegistry) AddAlias(target, source string) bool {
	if reg.parent != nil && !reg.parent.canAddFuncName(target, false) {
		return false
	}

	return reg.doAddAlias(target, source, true)
}

func (reg *funcRegistry) GetFunction(name string) (Function, bool) {
	reg.mx.RLock()
	defer reg.mx.RUnlock()

	if fn, ok := reg.nameToFunction[name]; ok {
		return fn, ok
	}

	if reg.parent != nil {
		return reg.parent.GetFunction(name)
	}

	return nil, false
}

func (reg *funcRegistry) GetFunctionNames() (out []string) {
	if reg.parent != nil {
		out = reg.parent.GetFunctionNames()
	} else {
		out = make([]string, 0, len(reg.nameToFunction))
	}
	reg.mx.RLock()
	defer reg.mx.RUnlock()

	out = append(out, slices.Collect(maps.Keys(reg.nameToFunction))...)
	slices.Sort(out)
	return
}

func (reg *funcRegistry) NumFunctions() (n int) {
	if reg.parent != nil {
		n = reg.parent.NumFunctions()
	}
	reg.mx.RLock()
	defer reg.mx.RUnlock()
	return n + len(reg.nameToFunction)
}

func (reg *funcRegistry) canAddFuncName(name string, allowOverwrite bool) bool {
	if reg.parent != nil {
		reg.parent.mx.RLock()
		defer reg.parent.mx.RUnlock()

		if !reg.parent.canAddFuncName(name, allowOverwrite) {
			return false
		}
	}
	if !allowOverwrite {
		_, ok := reg.nameToFunction[name]
		return !ok
	}
	return true
}

func (reg *funcRegistry) doAddFunction(fn Function, allowOverwrite bool, add bool) bool {
	debug.Assert(fn.Validate() == nil, "invalid function")

	lk := reg.getLocker(add)
	lk.Lock()
	defer lk.Unlock()

	name := fn.Name()
	if !reg.canAddFuncName(name, allowOverwrite) {
		return false
	}

	if add {
		reg.nameToFunction[name] = fn
	}
	return true
}

func (reg *funcRegistry) doAddAlias(target, source string, add bool) bool {
	// source name must exist in the registry or the parent
	// check outside the mutex, in case GetFunction has a mutex
	// acquisition
	fn, ok := reg.GetFunction(source)
	if !ok {
		return false
	}

	lk := reg.getLocker(add)
	lk.Lock()
	defer lk.Unlock()

	if !reg.canAddFuncName(target, false) {
		return false
	}

	if add {
		reg.nameToFunction[target] = fn
	}
	return true
}

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