prevent double free when closing capture library

Author: craigraw

src/main/java/com/sparrowwallet/sparrow/control/QRScanDialog.java

@@ -31,7 +31,6 @@
 import com.sparrowwallet.sparrow.io.bbqr.BBQRDecoder;
 import com.sparrowwallet.sparrow.io.bbqr.BBQRException;
 import com.sparrowwallet.sparrow.wallet.KeystoreController;
-import io.reactivex.Observable;
 import javafx.application.Platform;
 import javafx.beans.property.DoubleProperty;
 import javafx.beans.property.ObjectProperty;
@@ -58,7 +57,6 @@
 import java.nio.charset.StandardCharsets;
 import java.util.*;
 import java.util.List;
-import java.util.concurrent.TimeUnit;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
@@ -203,8 +201,7 @@ public QRScanDialog() {
 
             Platform.runLater(() -> {
                 webcamResolutionProperty.set(null);
-                Observable.just(this).delay(500, TimeUnit.MILLISECONDS)
-                        .subscribe(_ -> webcamService.close(), throwable -> log.error("Error closing webcam", throwable));
+                webcamService.close();
             });
         });
 

src/main/java/com/sparrowwallet/sparrow/control/WebcamService.java

@@ -39,6 +39,7 @@ public class WebcamService extends ScheduledService<Image> {
 
     private final Semaphore taskSemaphore = new Semaphore(1);
     private final AtomicBoolean cancelRequested = new AtomicBoolean(false);
+    private final AtomicBoolean captureClosed = new AtomicBoolean(false);
 
     private List<CaptureDevice> devices;
     private List<CaptureDevice> availableDevices;
@@ -112,7 +113,7 @@ public Task<Image> createTask() {
         return new Task<>() {
             @Override
             protected Image call() throws Exception {
-                if(cancelRequested.get() || isCancelled()) {
+                if(cancelRequested.get() || isCancelled() || captureClosed.get()) {
                     return null;
                 }
 
@@ -264,8 +265,11 @@ public boolean cancel() {
         return cancelled;
     }
 
-    public void close() {
-        capture.close();
+    public synchronized void close() {
+        if(!captureClosed.get()) {
+            captureClosed.set(true);
+            capture.close();
+        }
     }
 
     public PropertyLimits getZoomLimits() {