Create the wait-latch before running the action, and only if neeeded

Otherwise the result handler might be called before the wait-latch
has been created, leading to a deadlock of the thread.

Also: only wait for read- and write actions, but not for wait-actions.

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/btle/BtLEAction.java

@@ -22,6 +22,20 @@ public abstract class BtLEAction {
         this.characteristic = characteristic;
     }
 
+    /**
+     * Returns true if this actions expects an (async) result which must
+     * be waited for, before continuing with other actions.
+     *
+     * This is needed because the current Bluedroid stack can only deal
+     * with one single bluetooth operation at a time.
+     */
+    public abstract boolean expectsResult();
+
+    /**
+     * Executes this action, e.g. reads or write a GATT characteristic.
+     * @param gatt the characteristic to manipulate, or null if none.
+     * @return true if the action was successful, false otherwise
+     */
     public abstract boolean run(BluetoothGatt gatt);
 
     /**

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/btle/BtLEQueue.java

@@ -42,7 +42,7 @@ public final class BtLEQueue {
     private BluetoothGattCharacteristic mWaitCharacteristic;
     private GattCallback mExternalGattCallback;
 
-    private Thread dispatchThread = new Thread("Bluetooth GATT Dispatcher") {
+    private Thread dispatchThread = new Thread("GadgetBridge GATT Dispatcher") {
 
         @Override
         public void run() {
@@ -68,12 +68,17 @@ public final class BtLEQueue {
                     // Run all actions of the transaction until one doesn't succeed
                     for (BtLEAction action : transaction.getActions()) {
                         mWaitCharacteristic = action.getCharacteristic();
-                        if (action.run(mBluetoothGatt)) {
+                        boolean waitForResult = action.expectsResult();
+                        if (waitForResult) {
                             mWaitForActionResultLatch = new CountDownLatch(1);
-                            mWaitForActionResultLatch.await();
-                            mWaitForActionResultLatch = null;
-                            if (mAbortTransaction) {
-                                break;
+                        }
+                        if (action.run(mBluetoothGatt)) {
+                            if (waitForResult) {
+                                mWaitForActionResultLatch.await();
+                                mWaitForActionResultLatch = null;
+                                if (mAbortTransaction) {
+                                    break;
+                                }
                             }
                         } else {
                             LOG.error("Action returned false: " + action);
@@ -286,6 +291,10 @@ public final class BtLEQueue {
                 if (mWaitForActionResultLatch != null) {
                     mWaitForActionResultLatch.countDown();
                 }
+            } else {
+                if (BtLEQueue.this.mWaitCharacteristic != null) {
+                    LOG.error("checkWaitingCharacteristic: mismatched characteristic received: " + characteristic != null ? characteristic.getUuid().toString() : "(null)");
+                }
             }
         }
     };

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/btle/ReadAction.java

@@ -19,4 +19,9 @@ public class ReadAction extends BtLEAction {
     public boolean run(BluetoothGatt gatt) {
         return gatt.readCharacteristic(getCharacteristic());
     }
+
+    @Override
+    public boolean expectsResult() {
+        return true;
+    }
 }

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/btle/WaitAction.java

@@ -19,4 +19,10 @@ public class WaitAction extends BtLEAction {
             return false;
         }
     }
+
+    @Override
+    public boolean expectsResult() {
+        // no BT communication at all, no result
+        return false;
+    }
 }

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/btle/WriteAction.java

@@ -25,4 +25,9 @@ public class WriteAction extends BtLEAction {
         }
         return false;
     }
+
+    @Override
+    public boolean expectsResult() {
+        return true;
+    }
 }