Extract function to execute code on a handler

Extract function to synchronously execute code on a handler, waiting for
the execution to complete.

server/src/main/java/com/genymobile/scrcpy/opengl/OpenGLRunner.java

@@ -1,6 +1,7 @@
 package com.genymobile.scrcpy.opengl;
 
 import com.genymobile.scrcpy.device.Size;
+import com.genymobile.scrcpy.util.Threads;
 
 import android.graphics.SurfaceTexture;
 import android.opengl.EGL14;
@@ -15,6 +16,7 @@ import android.os.Handler;
 import android.os.HandlerThread;
 import android.view.Surface;
 
+import java.util.concurrent.Callable;
 import java.util.concurrent.Semaphore;
 
 public final class OpenGLRunner {
@@ -80,31 +82,17 @@ public final class OpenGLRunner {
     public Surface start(Size inputSize, Size outputSize, Surface outputSurface) throws OpenGLException {
         initOnce();
 
-        // Simulate CompletableFuture, but working for all Android versions
-        final Semaphore sem = new Semaphore(0);
-        Throwable[] throwableRef = new Throwable[1];
-
         // The whole OpenGL execution must be performed on a Handler, so that SurfaceTexture.setOnFrameAvailableListener() works correctly.
         // See <https://github.com/Genymobile/scrcpy/issues/5444>
-        handler.post(() -> {
-            try {
-                run(inputSize, outputSize, outputSurface);
-            } catch (Throwable throwable) {
-                throwableRef[0] = throwable;
-            } finally {
-                sem.release();
-            }
-        });
-
         try {
-            sem.acquire();
-        } catch (InterruptedException e) {
-            // Behave as if this method call was synchronous
-            Thread.currentThread().interrupt();
-        }
-
-        Throwable throwable = throwableRef[0];
-        if (throwable != null) {
+            Threads.executeSynchronouslyOn(handler, new Callable<Void>() {
+                @Override
+                public Void call() throws Exception {
+                    run(inputSize, outputSize, outputSurface);
+                    return null;
+                }
+            });
+        } catch (Throwable throwable) {
             if (throwable instanceof OpenGLException) {
                 throw (OpenGLException) throwable;
             }

server/src/main/java/com/genymobile/scrcpy/util/Threads.java

@@ -0,0 +1,43 @@
+package com.genymobile.scrcpy.util;
+
+import android.os.Handler;
+
+import java.util.concurrent.Callable;
+import java.util.concurrent.Semaphore;
+
+public final class Threads {
+    private Threads() {
+        // not instantiable
+    }
+
+    public static <T> T executeSynchronouslyOn(Handler handler, Callable<T> callable) throws Throwable {
+        // Simulate CompletableFuture, but working for all Android versions
+        final Semaphore sem = new Semaphore(0);
+        @SuppressWarnings("unchecked")
+        T[] resultRef = (T[]) new Object[1];
+        Throwable[] throwableRef = new Throwable[1];
+
+        handler.post(() -> {
+            try {
+                resultRef[0] = callable.call();
+            } catch (Throwable throwable) {
+                throwableRef[0] = throwable;
+            } finally {
+                sem.release();
+            }
+        });
+
+        try {
+            sem.acquire();
+        } catch (InterruptedException e) {
+            // Behave as if this method call was synchronous
+            Thread.currentThread().interrupt();
+        }
+
+        if (throwableRef[0] != null) {
+            throw throwableRef[0];
+        }
+
+        return resultRef[0];
+    }
+}