added store.callInReadTx()

Author: greenrobot

objectbox-java/src/main/java/io/objectbox/BoxStore.java

@@ -210,7 +210,7 @@ private static void verifyNotAlreadyOpen(String canonicalPath) {
  }
  }
  if (!openFiles.add(canonicalPath)) {
- throw new DbException("Another BoxStore is still open for this directory: " + canonicalPath+
+ throw new DbException("Another BoxStore is still open for this directory: " + canonicalPath +
  ". Hint: for most apps it's recommended to keep a BoxStore for the app's life time.");
  }
  }
@@ -492,6 +492,43 @@ public void runInReadTx(Runnable runnable) {
  }
  }
 
+ /**
+ * Calls the given callable inside a read(-only) transaction. Multiple read transactions can occur at the same time.
+ * This allows multiple read operations (gets) using a single consistent state of data.
+ * Also, for a high number of read operations (thousands, e.g. in loops),
+ * it is advised to run them in a single read transaction for efficiency reasons.
+ * Note that any exception thrown by the given Callable will be wrapped in a RuntimeException.
+ */
+ public <T> T callInReadTx(Callable<T> callable) {
+ Transaction tx = this.activeTx.get();
+ // Only if not already set, allowing to call it recursively with first (outer) TX
+ if (tx == null) {
+ tx = beginReadTx();
+ activeTx.set(tx);
+ try {
+ return callable.call();
+ } catch (Exception e) {
+ throw new RuntimeException("Callable threw exception", e);
+ } finally {
+ activeTx.remove();
+
+ // TODO That's rather a quick fix, replace with a more general solution
+ // (that could maybe be a TX listener with abort callback?)
+ for (Box box : boxes.values()) {
+ box.readTxFinished(tx);
+ }
+
+ tx.close();
+ }
+ } else {
+ try {
+ return callable.call();
+ } catch (Exception e) {
+ throw new RuntimeException("Callable threw exception", e);
+ }
+ }
+ }
+
  /**
  * Like {@link #runInTx(Runnable)}, but allows returning a value and throwing an exception.
  */

tests/objectbox-java-test/src/main/java/io/objectbox/TransactionTest.java

@@ -298,6 +298,26 @@ public void run() {
  assertEquals(1, counts[1]);
  }
 
+ @Test
+ public void testCallInReadTx() {
+ final Box<TestEntity> box = getTestEntityBox();
+ box.put(new TestEntity());
+ long[] counts = store.callInReadTx(new Callable<long[]>() {
+ @Override
+ public long[] call() throws Exception {
+ long count1 = store.callInReadTx(new Callable<Long>() {
+ @Override
+ public Long call() throws Exception {
+ return box.count();
+ }
+ });
+ return new long[]{box.count(), count1};
+ }
+ });
+ assertEquals(1, counts[0]);
+ assertEquals(1, counts[1]);
+ }
+
  @Test
  public void testRunInReadTxAndThenPut() {
  final Box<TestEntity> box = getTestEntityBox();