package backtype.storm.utils;
import org.apache.commons.io.FileUtils;
import java.io.File;
import java.util.Map;
import java.util.HashMap;
import java.io.IOException;
/**
* A simple, durable, atomic K/V database. *Very inefficient*, should only be
* used for occasional reads/writes. Every read/write hits disk.
*/
public class LocalState {
private VersionedStore _vs;
public LocalState(String backingDir) throws IOException {
_vs = new VersionedStore(backingDir);
}
public synchronized Map<Object, Object> snapshot() throws IOException {
int attempts = 0;
while (true) {
String latestPath = _vs.mostRecentVersionPath();
if (latestPath == null)
return new HashMap<Object, Object>();
try {
return (Map<Object, Object>) Utils.deserialize(FileUtils
.readFileToByteArray(new File(latestPath)));
} catch (IOException e) {
attempts++;
if (attempts >= 10) {
throw e;
}
}
}
}
public Object get(Object key) throws IOException {
return snapshot().get(key);
}
public synchronized void put(Object key, Object val) throws IOException {
put(key, val, true);
}
public synchronized void put(Object key, Object val, boolean cleanup)
throws IOException {
Map<Object, Object> curr = snapshot();
curr.put(key, val);
persist(curr, cleanup);
}
public synchronized void remove(Object key) throws IOException {
remove(key, true);
}
public synchronized void remove(Object key, boolean cleanup)
throws IOException {
Map<Object, Object> curr = snapshot();
curr.remove(key);
persist(curr, cleanup);
}
public synchronized void cleanup(int keepVersions) throws IOException {
_vs.cleanup(keepVersions);
}
private void persist(Map<Object, Object> val, boolean cleanup)
throws IOException {
byte[] toWrite = Utils.serialize(val);
String newPath = _vs.createVersion();
FileUtils.writeByteArrayToFile(new File(newPath), toWrite);
_vs.succeedVersion(newPath);
if (cleanup)
_vs.cleanup(4);
}
}