Add a new SingletonModule type
A SingletonModule is halfway between a Singleton and a Module. It has
access to visiting other modules via its GenerateSingletonBuildActions
method, but must be defined in an Android.bp file and can also be
depended on like a module.
Bug: 176904285
Test: singleton_module_test.go
Change-Id: I1b2bfdfb3927c1eabf431c53213cb7c581e33ca4
diff --git a/android/singleton_module.go b/android/singleton_module.go
new file mode 100644
index 0000000..2351738
--- /dev/null
+++ b/android/singleton_module.go
@@ -0,0 +1,146 @@
+// Copyright 2020 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 (
+ "fmt"
+ "sync"
+
+ "github.com/google/blueprint"
+)
+
+// A SingletonModule is halfway between a Singleton and a Module. It has access to visiting
+// other modules via its GenerateSingletonBuildActions method, but must be defined in an Android.bp
+// file and can also be depended on like a module. It must be used zero or one times in an
+// Android.bp file, and it can only have a single variant.
+//
+// The SingletonModule's GenerateAndroidBuildActions method will be called before any normal or
+// singleton module that depends on it, but its GenerateSingletonBuildActions method will be called
+// after all modules, in registration order with other singletons and singleton modules.
+// GenerateAndroidBuildActions and GenerateSingletonBuildActions will not be called if the
+// SingletonModule was not instantiated in an Android.bp file.
+//
+// Since the SingletonModule rules likely depend on the modules visited during
+// GenerateSingletonBuildActions, the GenerateAndroidBuildActions is unlikely to produce any
+// rules directly. Instead, it will probably set some providers to paths that will later have rules
+// generated to produce them in GenerateSingletonBuildActions.
+//
+// The expected use case for a SingletonModule is a module that produces files that depend on all
+// modules in the tree and will be used by other modules. For example it could produce a text
+// file that lists all modules that meet a certain criteria, and that text file could be an input
+// to another module. Care must be taken that the ninja rules produced by the SingletonModule
+// don't produce a cycle by referencing output files of rules of modules that depend on the
+// SingletonModule.
+//
+// A SingletonModule must embed a SingletonModuleBase struct, and its factory method must be
+// registered with RegisterSingletonModuleType from an init() function.
+//
+// A SingletonModule can also implement SingletonMakeVarsProvider to export values to Make.
+type SingletonModule interface {
+ Module
+ GenerateSingletonBuildActions(SingletonContext)
+ singletonModuleBase() *SingletonModuleBase
+}
+
+// SingletonModuleBase must be embedded into implementers of the SingletonModule interface.
+type SingletonModuleBase struct {
+ ModuleBase
+
+ lock sync.Mutex
+ bp string
+ variant string
+}
+
+// GenerateBuildActions wraps the ModuleBase GenerateBuildActions method, verifying it was only
+// called once to prevent multiple variants of a SingletonModule.
+func (smb *SingletonModuleBase) GenerateBuildActions(ctx blueprint.ModuleContext) {
+ smb.lock.Lock()
+ if smb.variant != "" {
+ ctx.ModuleErrorf("GenerateAndroidBuildActions already called for variant %q, SingletonModules can only have one variant", smb.variant)
+ }
+ smb.variant = ctx.ModuleSubDir()
+ smb.lock.Unlock()
+
+ smb.ModuleBase.GenerateBuildActions(ctx)
+}
+
+// InitAndroidSingletonModule must be called from the SingletonModule's factory function to
+// initialize SingletonModuleBase.
+func InitAndroidSingletonModule(sm SingletonModule) {
+ InitAndroidModule(sm)
+}
+
+// singletonModuleBase retrieves the embedded SingletonModuleBase from a SingletonModule.
+func (smb *SingletonModuleBase) singletonModuleBase() *SingletonModuleBase { return smb }
+
+// SingletonModuleFactory is a factory method that returns a SingletonModule.
+type SingletonModuleFactory func() SingletonModule
+
+// SingletonModuleFactoryAdaptor converts a SingletonModuleFactory into a SingletonFactory and a
+// ModuleFactory.
+func SingletonModuleFactoryAdaptor(name string, factory SingletonModuleFactory) (SingletonFactory, ModuleFactory) {
+ // The sm variable acts as a static holder of the only SingletonModule instance. Calls to the
+ // returned SingletonFactory and ModuleFactory lambdas will always return the same sm value.
+ // The SingletonFactory is only expected to be called once, but the ModuleFactory may be
+ // called multiple times if the module is replaced with a clone of itself at the end of
+ // blueprint.ResolveDependencies.
+ var sm SingletonModule
+ s := func() Singleton {
+ sm = factory()
+ return &singletonModuleSingletonAdaptor{sm}
+ }
+ m := func() Module {
+ if sm == nil {
+ panic(fmt.Errorf("Singleton %q for SingletonModule was not instantiated", name))
+ }
+
+ // Check for multiple uses of a SingletonModule in a LoadHook. Checking directly in the
+ // factory would incorrectly flag when the factory was called again when the module is
+ // replaced with a clone of itself at the end of blueprint.ResolveDependencies.
+ AddLoadHook(sm, func(ctx LoadHookContext) {
+ smb := sm.singletonModuleBase()
+ smb.lock.Lock()
+ defer smb.lock.Unlock()
+ if smb.bp != "" {
+ ctx.ModuleErrorf("Duplicate SingletonModule %q, previously used in %s", name, smb.bp)
+ }
+ smb.bp = ctx.BlueprintsFile()
+ })
+ return sm
+ }
+ return s, m
+}
+
+// singletonModuleSingletonAdaptor makes a SingletonModule into a Singleton by translating the
+// GenerateSingletonBuildActions method to Singleton.GenerateBuildActions.
+type singletonModuleSingletonAdaptor struct {
+ sm SingletonModule
+}
+
+// GenerateBuildActions calls the SingletonModule's GenerateSingletonBuildActions method, but only
+// if the module was defined in an Android.bp file.
+func (smsa *singletonModuleSingletonAdaptor) GenerateBuildActions(ctx SingletonContext) {
+ if smsa.sm.singletonModuleBase().bp != "" {
+ smsa.sm.GenerateSingletonBuildActions(ctx)
+ }
+}
+
+func (smsa *singletonModuleSingletonAdaptor) MakeVars(ctx MakeVarsContext) {
+ if smsa.sm.singletonModuleBase().bp != "" {
+ if makeVars, ok := smsa.sm.(SingletonMakeVarsProvider); ok {
+ makeVars.MakeVars(ctx)
+ }
+ }
+}