/**
* Check if the server has a given key. This is used for TPC operations that need to check whether
* or not a transaction can be performed but you don't want to modify the state of the cache by
* calling get(). You are allowed to call dataStore.get() for this method.
*
* @param key key to check for membership in store
*/
public boolean hasKey(String key) {
try {
dataStore.get(key);
} catch (KVException e) { // an exception of key_not_found is caught
return false;
}
return true;
}
/**
* Performs del request.
*
* @param key String key
* @throws KVException with ERROR_NO_SUCH_KEY if key does not exist in store
*/
@Override
public void del(String key) throws KVException {
if (key.length() > MAX_KEY_SIZE) {
KVMessage msg = new KVMessage(KVConstants.RESP, ERROR_NO_SUCH_KEY);
throw new KVException(msg);
}
Lock lock = dataCache.getLock(key);
try {
lock.lock();
dataCache.del(key);
dataStore.del(key);
} finally {
lock.unlock();
}
}
/**
* Performs put request on cache and store.
*
* @param key String key
* @param value String value
* @throws KVException if key or value is too long
*/
@Override
public void put(String key, String value) throws KVException {
if (key.length() > MAX_KEY_SIZE) {
KVMessage msg = new KVMessage(KVConstants.RESP, ERROR_OVERSIZED_KEY);
throw new KVException(msg);
}
if (value.length() > MAX_VAL_SIZE) {
KVMessage msg = new KVMessage(KVConstants.RESP, ERROR_OVERSIZED_VALUE);
throw new KVException(msg);
}
Lock lock = dataCache.getLock(key);
try {
// In case of some unexpected exception thrown here
lock.lock();
dataCache.put(key, value);
dataStore.put(key, value);
} finally {
lock.unlock();
}
}
/**
* Performs get request. Checks cache first. Updates cache if not in cache but located in store.
*
* @param key String key
* @return String value associated with key
* @throws KVException with ERROR_NO_SUCH_KEY if key does not exist in store
*/
@Override
public String get(String key) throws KVException {
if (key.length() > MAX_KEY_SIZE) {
KVMessage msg = new KVMessage(KVConstants.RESP, ERROR_NO_SUCH_KEY);
throw new KVException(msg);
}
Lock lock = dataCache.getLock(key);
String ret = null;
try {
lock.lock();
ret = dataCache.get(key);
if (ret == null) {
ret = dataStore.get(key);
if (ret != null) dataCache.put(key, ret);
}
} finally {
lock.unlock();
}
return ret;
}
/** This method is purely for convenience and will not be tested. */
@Override
public String toString() {
return dataStore.toString() + dataCache.toString();
}