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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.concurrent;
import com.yahoo.concurrent.ThreadLocalDirectory.ObservableUpdater;
import com.yahoo.concurrent.ThreadLocalDirectory.Updater;
/**
* Only for use along with ThreadLocalDirectory. A thread local data container
* instance. The class is visible to avoid indirection through the internal
* {@link ThreadLocal} in ThreadLocalDirectory if possible, but has no user
* available methods.
*
* @param <AGGREGATOR> the structure to insert produced data into
* @param <SAMPLE> type of produced data to insert from each participating thread
* @author Steinar Knutsen
*/
public final class LocalInstance<AGGREGATOR, SAMPLE> {
/**
* The current generation of data produced from a single thread, where
* generation is the period between two subsequent calls to
* ThreadLocalDirectory.fetch().
*/
private AGGREGATOR current;
// see comment on setRegistered(boolean) for locking explanation
private boolean isRegistered = false;
private final Object lock = new Object();
LocalInstance(Updater<AGGREGATOR, SAMPLE> updater) {
current = updater.createGenerationInstance(null);
}
boolean update(SAMPLE x, Updater<AGGREGATOR, SAMPLE> updater) {
synchronized (lock) {
current = updater.update(current, x);
return isRegistered;
}
}
AGGREGATOR getAndReset(Updater<AGGREGATOR, SAMPLE> updater) {
AGGREGATOR previous;
synchronized (lock) {
previous = current;
current = updater.createGenerationInstance(previous);
setRegistered(false);
}
return previous;
}
AGGREGATOR copyCurrent(ObservableUpdater<AGGREGATOR, SAMPLE> updater) {
AGGREGATOR view;
synchronized (lock) {
view = updater.copy(current);
}
return view;
}
// This is either set by the putting thread or the fetching thread. If
// it is set by the putting thread, then there is no memory barrier,
// because it is only _read_ in the putting thread. If it is set by the
// fetching thread, then the memory barrier is this.lock. This
// roundabout way is to avoid creating many-to-many memory barrier and
// locking relationships.
void setRegistered(boolean isRegistered) {
this.isRegistered = isRegistered;
}
}
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