app, cmd/gomobile: expose an app.State variable

The State can be used in the Start callback (and lazily-initialized
packages) instead of JavaInit. This stores a reference to the
android.context.Context for the (future) keyboard package and for
setting TMPDIR.

Second attempt at https://golang.org/cl/4400.

Change-Id: I673997b26ab25ce5140cb31950593d8c6dbd9c51
Reviewed-on: https://go-review.googlesource.com/5555
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

app/Go.java

@@ -13,7 +13,7 @@ import android.util.Log;
 // Go code.
 public final class Go {
 	// init loads libgojni.so and starts the runtime.
-	public static void init(Context context) {
+	public static void init(final Context ctx) {
 		if (Looper.myLooper() != Looper.getMainLooper()) {
 			Log.wtf("Go", "Go.init must be called from main thread (looper="+Looper.myLooper().toString()+")");
 		}
@@ -29,7 +29,7 @@ public final class Go {
 
 		new Thread("GoMain") {
 			public void run() {
-				Go.run();
+				Go.run(ctx);
 			}
 		}.start();
 
@@ -42,6 +42,6 @@ public final class Go {
 
 	private static boolean running = false;
 
-	private static native void run();
+	private static native void run(Context ctx);
 	private static native void waitForRun();
 }

app/android.c

@@ -15,16 +15,13 @@
 #include <string.h>
 #include "_cgo_export.h"
 
-// Defined in android.go.
-extern pthread_cond_t go_started_cond;
-extern pthread_mutex_t go_started_mu;
-extern int go_started;
-extern JavaVM* current_vm;
-
+// Defined in the Go runtime.
 static int (*_rt0_arm_linux1)(int argc, char** argv);
 
 jint JNI_OnLoad(JavaVM* vm, void* reserved) {
 	current_vm = vm;
+	current_ctx = NULL;
+	current_native_activity = NULL;
 
 	JNIEnv* env;
 	if ((*vm)->GetEnv(vm, (void**)&env, JNI_VERSION_1_6) != JNI_OK) {
@@ -92,7 +89,10 @@ void InitGoRuntime() {
 
 // Runtime entry point when using NativeActivity.
 void ANativeActivity_onCreate(ANativeActivity *activity, void* savedState, size_t savedStateSize) {
+	// Note that activity->clazz is mis-named.
 	current_vm = activity->vm;
+	current_ctx = (*activity->env)->NewGlobalRef(activity->env, activity->clazz);
+	current_native_activity = activity;
 
 	InitGoRuntime();
 
@@ -121,7 +121,8 @@ void ANativeActivity_onCreate(ANativeActivity *activity, void* savedState, size_
 
 // Runtime entry point when embedding Go in a Java App.
 JNIEXPORT void JNICALL
-Java_go_Go_run(JNIEnv* env, jclass clazz) {
+Java_go_Go_run(JNIEnv* env, jclass clazz, jobject ctx) {
+	current_ctx = (*env)->NewGlobalRef(env, ctx);
 	init_go_runtime(NULL);
 }
 

app/android.go

@@ -34,6 +34,12 @@ int go_started;
 // on android.
 JavaVM* current_vm;
 
+// current_ctx is Android's android.context.Context. May be NULL.
+jobject current_ctx;
+
+// current_native_activity is the Android ANativeActivity. May be NULL.
+ANativeActivity* current_native_activity;
+
 // build_auxv builds an ELF auxiliary vector for initializing the Go
 // runtime. While there does not appear to be any spec for this
 // format, there are some notes in
@@ -166,10 +172,16 @@ func onConfigurationChanged(activity *C.ANativeActivity) {
 func onLowMemory(activity *C.ANativeActivity) {
 }
 
-// JavaInit is an initialization function registered by the package
-// golang.org/x/mobile/bind/java. It gives the Java language
-// bindings access to the JNI *JavaVM object.
-var JavaInit func(javaVM uintptr)
+type androidState struct {
+}
+
+func (androidState) JavaVM() unsafe.Pointer {
+	return unsafe.Pointer(C.current_vm)
+}
+
+func (androidState) AndroidContext() unsafe.Pointer {
+	return unsafe.Pointer(C.current_ctx)
+}
 
 var (
 	windowDestroyed = make(chan bool)
@@ -227,6 +239,23 @@ func (a *asset) Close() error {
 	return nil
 }
 
+func runStart(cb Callbacks) {
+	State = androidState{}
+
+	if cb.Start != nil {
+		cb.Start()
+	}
+}
+
+// notifyInitDone informs Java that the program is initialized.
+// A NativeActivity will not create a window until this is called.
+func notifyInitDone() {
+	C.pthread_mutex_lock(&C.go_started_mu)
+	C.go_started = 1
+	C.pthread_cond_signal(&C.go_started_cond)
+	C.pthread_mutex_unlock(&C.go_started_mu)
+}
+
 func run(cb Callbacks) {
 	// We want to keep the event loop on a consistent OS thread.
 	runtime.LockOSThread()
@@ -237,20 +266,12 @@ func run(cb Callbacks) {
 	C.free(unsafe.Pointer(ctag))
 	C.free(unsafe.Pointer(cstr))
 
-	if JavaInit != nil {
-		JavaInit(uintptr(unsafe.Pointer(C.current_vm)))
-	}
-
-	// Inform Java that the program is initialized.
-	C.pthread_mutex_lock(&C.go_started_mu)
-	C.go_started = 1
-	C.pthread_cond_signal(&C.go_started_cond)
-	C.pthread_mutex_unlock(&C.go_started_mu)
-
-	for {
-		select {
-		case w := <-windowCreated:
-			windowDrawLoop(cb, w, queue)
-		}
+	if C.current_native_activity == nil {
+		runStart(cb)
+		notifyInitDone()
+		select {}
+	} else {
+		notifyInitDone()
+		windowDrawLoop(cb, <-windowCreated, queue)
 	}
 }

app/app.go

@@ -25,8 +25,12 @@ type Callbacks struct {
 	// Start is called when the app enters the foreground.
 	// The app will start receiving Draw and Touch calls.
 	//
-	// Window geometry will be configured and an OpenGL context
-	// will be available.
+	// If the app is responsible for the screen (that is, it is an
+	// all-Go app), then Window geometry will be configured and an
+	// OpenGL context will be available during Start.
+	//
+	// If this is a library, Start will be called before the
+	// app is told that Go has finished initialization.
 	//
 	// Start is an equivalent lifecycle state to onStart() on
 	// Android and applicationDidBecomeActive on iOS.
@@ -82,3 +86,17 @@ type ReadSeekCloser interface {
 	io.ReadSeeker
 	io.Closer
 }
+
+// State is global application-specific state.
+//
+// The State variable also holds operating system specific state.
+// Android apps have the extra methods:
+//
+//	// JavaVM returns a JNI *JavaVM.
+//	JavaVM() unsafe.Pointer
+//
+//	// AndroidContext returns a jobject for the app android.context.Context.
+//	AndroidContext() unsafe.Pointer
+//
+// State is not valid until Run has been called.
+var State interface{}

app/loop_android.go

@@ -101,6 +101,9 @@ func windowDrawLoop(cb Callbacks, w *C.ANativeWindow, queue *C.AInputQueue) {
 	geom.Width = geom.Pt(float32(C.windowWidth) / geom.PixelsPerPt)
 	geom.Height = geom.Pt(float32(C.windowHeight) / geom.PixelsPerPt)
 
+	// Wait until geometry and GL is initialized before cb.Start.
+	runStart(cb)
+
 	// We start here rather than onStart so the window exists and the Gl
 	// context is configured.
 	if cb.Start != nil {

bind/java/javatest.go

@@ -8,11 +8,11 @@ package main
 
 import (
 	"golang.org/x/mobile/app"
+	"golang.org/x/mobile/bind/java"
 
-	_ "golang.org/x/mobile/bind/java"
 	_ "golang.org/x/mobile/bind/java/testpkg/go_testpkg"
 )
 
 func main() {
-	app.Run(app.Callbacks{})
+	app.Run(app.Callbacks{Start: java.Init})
 }

bind/java/seq_android.go

@@ -78,10 +78,13 @@ func init() {
 	res.out = make(map[int32]*seq.Buffer)
 }
 
-func init() {
-	app.JavaInit = func(javaVM uintptr) {
-		C.init_seq(unsafe.Pointer(javaVM))
-	}
+// Init initializes communication with Java.
+// Typically called from the Start callback in app.Run.
+func Init() {
+	vm := app.State.(interface {
+		JavaVM() unsafe.Pointer
+	}).JavaVM()
+	C.init_seq(vm)
 }
 
 func seqToBuf(bufptr **C.uint8_t, lenptr *C.size_t, buf *seq.Buffer) {

cmd/gomobile/bind.go

@@ -295,13 +295,13 @@ var androidMainTmpl = template.Must(template.New("android.go").Parse(`
 package main
 
 import (
-        "golang.org/x/mobile/app"
+	"golang.org/x/mobile/app"
+	"golang.org/x/mobile/bind/java"
 
-        _ "golang.org/x/mobile/bind/java"
-        _ "{{.}}"
+	_ "{{.}}"
 )
 
 func main() {
-        app.Run(app.Callbacks{})
+	app.Run(app.Callbacks{Start: java.Init})
 }
 `))