ipc/android: Add a blocking connect Java method, and small clean-ups.

src/xrt/ipc/android/src/main/AndroidManifest.xml

@@ -5,7 +5,11 @@
         SPDX-License-Identifier: BSL-1.0
     -->
     <application>
-        <service android:name=".MonadoService" android:enabled="true" android:exported="true" android:externalService="true">
+        <service
+            android:name=".MonadoService"
+            android:enabled="true"
+            android:exported="true"
+            android:externalService="true">
             <intent-filter>
                 <action android:name="org.freedesktop.monado.CONNECT" />
             </intent-filter>

src/xrt/ipc/android/src/main/java/org/freedesktop/monado/ipc/Client.java

@@ -21,6 +21,8 @@ import android.util.Log;
 
 import androidx.annotation.Keep;
 
+import org.freedesktop.monado.auxiliary.NativeCounterpart;
+
 import java.io.IOException;
 
 /**
@@ -31,49 +33,103 @@ import java.io.IOException;
 @Keep
 public class Client implements ServiceConnection {
     private static final String TAG = "monado-ipc-client";
-
     /**
-     * Context provided by app.
+     * Used to block native until we have our side of the socket pair.
      */
-    private Context context;
-
+    private final Object connectSync = new Object();
     /**
      * Pointer to local IPC proxy: calling methods on it automatically transports arguments across binder IPC.
      * <p>
      * May be null!
      */
-    public IMonado monado;
-
-    /**
-     * "Our" side of the socket pair - the other side is sent to the server automatically on connection.
-     */
-    public ParcelFileDescriptor fd;
-
+    @Keep
+    public IMonado monado = null;
     /**
      * Indicates that we tried to connect but failed.
      * <p>
      * Used to distinguish a "not yet fully connected" null monado member from a "tried and failed"
      * null monado member.
      */
+    @Keep
     public boolean failed = false;
+    /**
+     * Keep track of the ipc_client_android instance over on the native side.
+     */
+    private final NativeCounterpart nativeCounterpart;
+    /**
+     * "Our" side of the socket pair - the other side is sent to the server automatically on connection.
+     */
+    private ParcelFileDescriptor fd = null;
+    /**
+     * Context provided by app.
+     */
+    private Context context;
 
     /**
-     * Bind to the Monado IPC service - this asynchronously starts connecting (and launching the
-     * service if it's not already running)
+     * Constructor
+     *
+     * @param nativePointer the corresponding native object's pointer.
+     */
+    @Keep
+    public Client(long nativePointer) {
+        this.nativeCounterpart = new NativeCounterpart(nativePointer);
+        this.nativeCounterpart.markAsUsedByNativeCode();
+    }
+
+    /**
+     * Let the native code notify us that it is no longer using this class.
+     */
+    @Keep
+    public void markAsDiscardedByNative() {
+        nativeCounterpart.markAsDiscardedByNative(TAG);
+    }
+
+    /**
+     * Bind to the Monado IPC service, and block until it is fully connected.
      * <p>
      * The IPC client code on Android should load this class (from the right package), instantiate
-     * this class, and call this method.
+     * this class (retaining a reference to it!), and call this method.
      *
      * @param context_    Context to use to make the connection. (We get the application context
      *                    from it.)
      * @param packageName The package name containing the Monado runtime. The caller is guaranteed
      *                    to know this because it had to load this class from that package.
-     *                    (Often "org.freedesktop.monado.openxr.out_of_process" for now, at least)
-     * @todo how to get the right package name here? Do we have to go so far as to re-enumerate ourselves?
+     *                    There's a define in xrt_config_android.h to use for this.
+     * @return the fd number - do not close! (dup if you want to be able to close it) Returns -1 if
+     * something went wrong.
      * <p>
      * Various builds, variants, etc. will have different package names, but we must specify the
      * package name explicitly to avoid violating security restrictions.
      */
+    @Keep
+    public int blockingConnect(Context context_, String packageName) {
+        synchronized (connectSync) {
+            bind(context_, packageName);
+            try {
+                while (fd == null) {
+                    connectSync.wait();
+                }
+            } catch (InterruptedException e) {
+                return -1;
+            }
+        }
+        return fd.getFd();
+    }
+
+    /**
+     * Bind to the Monado IPC service - this asynchronously starts connecting (and launching the
+     * service if it's not already running)
+     *
+     * @param context_    Context to use to make the connection. (We get the application context
+     *                    from it.)
+     * @param packageName The package name containing the Monado runtime. The caller is guaranteed
+     *                    to know this because it had to load this class from that package.
+     *                    There's a define in xrt_config_android.h to use for this.
+     *                    <p>
+     *                    Various builds, variants, etc. will have different package names, but we
+     *                    must specify the package name explicitly to avoid violating security
+     *                    restrictions.
+     */
     public void bind(Context context_, String packageName) {
         context = context_.getApplicationContext();
         if (context == null) {
@@ -110,9 +166,10 @@ public class Client implements ServiceConnection {
     public void onServiceConnected(ComponentName name, IBinder service) {
         monado = IMonado.Stub.asInterface(service);
         ParcelFileDescriptor theirs;
+        ParcelFileDescriptor ours;
         try {
             ParcelFileDescriptor[] fds = ParcelFileDescriptor.createSocketPair();
-            fd = fds[0];
+            ours = fds[0];
             theirs = fds[1];
         } catch (IOException e) {
             e.printStackTrace();
@@ -126,6 +183,10 @@ public class Client implements ServiceConnection {
             e.printStackTrace();
             Log.e(TAG, "could not call IMonado.connect: " + e.toString());
             handleFailure();
+            return;
+        }
+        synchronized (connectSync) {
+            fd = ours;
         }
     }
 
@@ -137,6 +198,7 @@ public class Client implements ServiceConnection {
     @Override
     public void onServiceDisconnected(ComponentName name) {
         monado = null;
+        //! @todo tell native that the world is crumbling, then close the fd here.
     }
 
     /*

src/xrt/ipc/android/src/main/java/org/freedesktop/monado/ipc/MonadoImpl.java

@@ -15,18 +15,25 @@ import android.view.Surface;
 
 import androidx.annotation.Keep;
 
-import org.freedesktop.monado.ipc.IMonado.Stub;
-
 /**
  * Java implementation of the IMonado IPC interface.
- *
+ * <p>
+ * (This is the server-side code.)
+ * <p>
  * All this does is delegate calls to native JNI implementations
  */
+@SuppressWarnings("JavaJniMissingFunction")
 @Keep
 public class MonadoImpl extends IMonado.Stub {
 
+    static {
+        // Load the shared library with the native parts of this class
+        // This is the service-lib target.
+        System.loadLibrary("monado-service");
+    }
+
     public void connect(ParcelFileDescriptor parcelFileDescriptor) {
-        nativeAddClient(parcelFileDescriptor);
+        nativeAddClient(parcelFileDescriptor.detachFd());
     }
 
     public void passAppSurface(Surface surface) {
@@ -36,13 +43,13 @@ public class MonadoImpl extends IMonado.Stub {
     /**
      * Native handling of receiving a surface: should convert it to an ANativeWindow then do stuff
      * with it.
-     *
+     * <p>
      * Ignore Android Studio complaining that this function is missing: it is not, it is just in a
      * different module. See `src/xrt/targets/service-lib/lib.cpp` for the implementation.
      * (Ignore the warning saying that file isn't included in the build: it is, Android Studio
      * is just confused.)
      *
-     * @param surface
+     * @param surface The surface to pass to native code
      * @todo figure out a good way to make the MonadoImpl pointer a client ID
      */
     private native void nativeAppSurface(Surface surface);
@@ -50,24 +57,18 @@ public class MonadoImpl extends IMonado.Stub {
     /**
      * Native handling of receiving an FD for a new client: the FD should be used to start up the
      * rest of the native IPC code on that socket.
-     *
+     * <p>
      * This is essentially the entry point for the monado service on Android: if it's already
      * running, this will be called in it. If it's not already running, a process will be created,
      * and this will be the first native code executed in that process.
-     *
+     * <p>
      * Ignore Android Studio complaining that this function is missing: it is not, it is just in a
      * different module. See `src/xrt/targets/service-lib/lib.cpp` for the implementation.
      * (Ignore the warning saying that file isn't included in the build: it is, Android Studio
      * is just confused.)
      *
-     * @param surface
+     * @param fd The incoming file descriptor: ownership is transferred to native code here.
      * @todo figure out a good way to make the MonadoImpl pointer a client ID
      */
-    private native void nativeAddClient(ParcelFileDescriptor parcelFileDescriptor);
-
-    static {
-        // Load the shared library with the native parts of this class
-        // This is the service-lib target.
-        System.loadLibrary("monado-service");
-    }
+    private native void nativeAddClient(int fd);
 }

src/xrt/ipc/android/src/main/java/org/freedesktop/monado/ipc/MonadoService.java

@@ -18,7 +18,7 @@ import androidx.annotation.Nullable;
 
 /**
  * Minimal implementation of a Service.
- *
+ * <p>
  * This is needed so that the APK can expose the binder service implemented in MonadoImpl.
  */
 public class MonadoService extends Service {