Add DeviceConfig and OncePer objects

Add DeviceConfig to store per-device configuration information.  Put a
OncePer object inside Config and DeviceConfig, which computes a value
once per key per object to allow build logic to store arbitrary
per-build or per-device computed values.

Change-Id: I1a38b426f29d223ef5e803e0d4d9604500de2fd2

Android.bp

@@ -100,6 +100,7 @@ bootstrap_go_package {
         "android/makevars.go",
         "android/module.go",
         "android/mutator.go",
+        "android/onceper.go",
         "android/package_ctx.go",
         "android/paths.go",
         "android/util.go",

android/arch.go

@@ -717,7 +717,7 @@ func forEachInterface(v reflect.Value, f func(reflect.Value)) {
 }
 
 // Convert the arch product variables into a list of targets for each os class structs
-func decodeTargetProductVariables(config Config) (map[OsClass][]Target, error) {
+func decodeTargetProductVariables(config *config) (map[OsClass][]Target, error) {
 	variables := config.ProductVariables
 
 	targets := make(map[OsClass][]Target)

android/config.go

@@ -43,11 +43,18 @@ func (f *FileConfigurableOptions) SetDefaultConfig() {
 	*f = FileConfigurableOptions{}
 }
 
+// A Config object represents the entire build configuration for Android.
 type Config struct {
 	*config
 }
 
-// A config object represents the entire build configuration for Android.
+// A DeviceConfig object represents the configuration for a particular device being built.  For
+// now there will only be one of these, but in the future there may be multiple devices being
+// built
+type DeviceConfig struct {
+	*deviceConfig
+}
+
 type config struct {
 	FileConfigurableOptions
 	ProductVariables productVariables
@@ -58,6 +65,8 @@ type config struct {
 	Targets        map[OsClass][]Target
 	BuildOsVariant string
 
+	deviceConfig *deviceConfig
+
 	srcDir   string // the path of the root source directory
 	buildDir string // the path of the build output directory
 
@@ -66,6 +75,13 @@ type config struct {
 	envFrozen bool
 
 	inMake bool
+	OncePer
+}
+
+type deviceConfig struct {
+	config  *config
+	targets []Arch
+	OncePer
 }
 
 type jsonConfigurable interface {
@@ -138,17 +154,23 @@ func saveToConfigFile(config jsonConfigurable, filename string) error {
 // the root source directory. It also loads the config file, if found.
 func NewConfig(srcDir, buildDir string) (Config, error) {
 	// Make a config with default options
-	config := Config{
-		config: &config{
-			ConfigFileName:           filepath.Join(buildDir, configFileName),
-			ProductVariablesFileName: filepath.Join(buildDir, productVariablesFileName),
+	config := &config{
+		ConfigFileName:           filepath.Join(buildDir, configFileName),
+		ProductVariablesFileName: filepath.Join(buildDir, productVariablesFileName),
 
-			srcDir:   srcDir,
-			buildDir: buildDir,
-			envDeps:  make(map[string]string),
-		},
+		srcDir:   srcDir,
+		buildDir: buildDir,
+		envDeps:  make(map[string]string),
+
+		deviceConfig: &deviceConfig{},
 	}
 
+	deviceConfig := &deviceConfig{
+		config: config,
+	}
+
+	config.deviceConfig = deviceConfig
+
 	// Sanity check the build and source directories. This won't catch strange
 	// configurations with symlinks, but at least checks the obvious cases.
 	absBuildDir, err := filepath.Abs(buildDir)
@@ -166,7 +188,7 @@ func NewConfig(srcDir, buildDir string) (Config, error) {
 	}
 
 	// Load any configurable options from the configuration file
-	err = loadConfig(config.config)
+	err = loadConfig(config)
 	if err != nil {
 		return Config{}, err
 	}
@@ -192,7 +214,7 @@ func NewConfig(srcDir, buildDir string) (Config, error) {
 	config.Targets = targets
 	config.BuildOsVariant = targets[Host][0].String()
 
-	return config, nil
+	return Config{config}, nil
 }
 
 func (c *config) RemoveAbandonedFiles() bool {
@@ -337,3 +359,11 @@ func (c *config) Android64() bool {
 
 	return false
 }
+
+func (c *deviceConfig) Arches() []Arch {
+	var arches []Arch
+	for _, target := range c.config.Targets[Device] {
+		arches = append(arches, target.Arch)
+	}
+	return arches
+}

android/module.go

@@ -56,6 +56,7 @@ type androidBaseContext interface {
 	Darwin() bool
 	Debug() bool
 	AConfig() Config
+	DeviceConfig() DeviceConfig
 }
 
 type BaseContext interface {
@@ -535,6 +536,10 @@ func (a *androidBaseContextImpl) AConfig() Config {
 	return a.config
 }
 
+func (a *androidBaseContextImpl) DeviceConfig() DeviceConfig {
+	return DeviceConfig{a.config.deviceConfig}
+}
+
 func (a *androidModuleContext) Proprietary() bool {
 	return a.module.base().commonProperties.Proprietary
 }

android/onceper.go

@@ -0,0 +1,75 @@
+// Copyright 2016 Google Inc. All rights reserved.
+//
+// Licensed 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.
+
+package android
+
+import (
+	"sync"
+	"sync/atomic"
+)
+
+type OncePer struct {
+	values     atomic.Value
+	valuesLock sync.Mutex
+}
+
+type valueMap map[interface{}]interface{}
+
+// Once computes a value the first time it is called with a given key per OncePer, and returns the
+// value without recomputing when called with the same key.  key must be hashable.
+func (once *OncePer) Once(key interface{}, value func() interface{}) interface{} {
+	// Atomically load the map without locking.  If this is the first call Load() will return nil
+	// and the type assertion will fail, leaving a nil map in m, but that's OK since m is only used
+	// for reads.
+	m, _ := once.values.Load().(valueMap)
+	if v, ok := m[key]; ok {
+		return v
+	}
+
+	once.valuesLock.Lock()
+	defer once.valuesLock.Unlock()
+
+	// Check again with the lock held
+	m, _ = once.values.Load().(valueMap)
+	if v, ok := m[key]; ok {
+		return v
+	}
+
+	// Copy the existing map
+	newMap := make(valueMap, len(m))
+	for k, v := range m {
+		newMap[k] = v
+	}
+
+	v := value()
+
+	newMap[key] = v
+	once.values.Store(newMap)
+
+	return v
+}
+
+func (once *OncePer) OnceStringSlice(key interface{}, value func() []string) []string {
+	return once.Once(key, func() interface{} { return value() }).([]string)
+}
+
+func (once *OncePer) Once2StringSlice(key interface{}, value func() ([]string, []string)) ([]string, []string) {
+	type twoStringSlice [2][]string
+	s := once.Once(key, func() interface{} {
+		var s twoStringSlice
+		s[0], s[1] = value()
+		return s
+	}).(twoStringSlice)
+	return s[0], s[1]
+}