如何使用BinaryHandler正确在微流存储长volatile数组?

Question

我试图存储Eclipse Collection的LongArrayList (https://www.eclipse.org/collections/)与Microstream，但由于它的"items"字段是瞬态的，这不能开箱运行。

我所做的就是创建一个新的类persistableelongarraylist，像这样:

public class PersistableLongArrayList extends LongArrayList {
static BinaryTypeHandler<PersistableLongArrayList> provideTypeHandler() {
return Binary.TypeHandler(PersistableLongArrayList.class,
Binary.Field_int(
"size", 
list -> list.size, 
(list, value) -> list.size = value
),
Binary.Field(
long[].class, "items", 
list -> list.items, 
(list, value) -> list.items = value
)
);
} 
}

项目字段现在不是空时，从存储实例加载，但是，如果我改变值之后调用storage.store(list)，关闭数据库并重新启动它的新值不存储，只有大小被正确存储。

我添加了一个非常简单的例子来显示这种行为:

public class SimpleTest {
private PersistableLongArrayList root;
public static void main(String[] args) {
try {
SimpleTest t = new SimpleTest();
// DB erstellen
EmbeddedStorageManager storage = t.startDB();
// modify the list
t.root.add(t.root.size() + 1);
storage.store(t.root);
// stop DB
t.stopDB(storage);
// restart DB
storage = t.startDB();
// show root element
System.out.println(t.root);
// Observed behavior: list "grows" from s.th. like this: [1] to s.th. like this [1, 0, 0, 0] after several runs (Probably only size grows and is stored correctly and therefore the fields up to "size" are printed but empty)
// Expected beahvior: list starts with [1] and grows to something like this [1, 2, 3, 4] after several runs
} catch (Throwable t) {
t.printStackTrace();
} finally {
System.exit(0);
}
}
private EmbeddedStorageManager startDB() {
EmbeddedStorageManager storageManager = EmbeddedStorage.start();
if(storageManager.root() == null) {
PersistableLongArrayList list = new PersistableLongArrayList();
storageManager.setRoot(list);
storageManager.storeRoot();
root = list;
} else {
root = (PersistableLongArrayList)storageManager.root();
}
return storageManager;
}
private void stopDB(EmbeddedStorageManager storageManager) {
storageManager.shutdown();
}
}

可能我只是误解了如何正确使用自定义BinaryHandler，但我不知道现在要改变什么。任何建议都很感激:)

亲切的问候,托马斯。

Answer 1

使用自定义PersistenceEagerStoringFieldEvaluator和PersistenceFieldEvaluator可以直接持久化LongArrayList:

public class PersistenceFieldEvaluatorCustom implements PersistenceFieldEvaluator {
@Override
public boolean applies(final Class<?> entityType, final Field field) {
//return true if field should be persisted, false if not
if(entityType == org.eclipse.collections.impl.list.mutable.primitive.LongArrayList.class && field.getName().equals("items")) {
return true;
}
//default: return false if field has the transient modifier
return !XReflect.isTransient(field);
}
}

public class PersistenceEagerStoringFieldEvaluatorCustom implements PersistenceEagerStoringFieldEvaluator {
@Override
public boolean isEagerStoring(final Class<?> t, final Field u) {
//return true if field should be persisted at every store
if(t == org.eclipse.collections.impl.list.mutable.primitive.LongArrayList.class && u.getName().equals("items")) {
return true;
}
return false;
}
}

设置:

final EmbeddedStorageManager s = EmbeddedStorage.Foundation()
.onConnectionFoundation(
c->{ c.setFieldEvaluatorPersistable(new PersistenceFieldEvaluatorCustom());
c.setReferenceFieldEagerEvaluator(new PersistenceEagerStoringFieldEvaluatorCustom());
})
.start();

问好详情请参阅https://github.com/microstream-one/microstream/discussions/247