Hi all,
I need help!
I'm using concurrent tasks executed in a task queue. Let's say I want
to spawn 100 concurrent tasks and do something once they are all done.
I thought this is simple by just storing the total number of spawned
tasks into the datastore and let each task decrease the number by 1.
The value should be 0 when all tasks are done.
This is my code snippet to decrease the value:
Transaction tx = datastore.beginTransaction();
try {
Entity entity = datastore.get(tx, KeyFactory.createKey(kind, key));
Long number = (Long) entity.getProperty(column);
if (number == null || number == 0) {
tx.commit();
return 0;
}
number -= 1;
entity.setProperty(column, number);
datastore.put(tx, entity);
tx.commit();
return number;
} catch (Exception e) {
throw new DBException("Failed to decrease counter, force retry!", e);
} finally {
if (tx.isActive()) {
tx.rollback();
}
}
Something must be wrong with my code as from time to time two
concurrent tasks return the same number after decreasing the value.
Can someone please give me an advice?
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