org.neo4j.dbms.database.readonly.DatabaseReadOnlyChecker Maven / Gradle / Ivy
/*
* Copyright (c) "Neo4j"
* Neo4j Sweden AB [https://neo4j.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see .
*/
package org.neo4j.dbms.database.readonly;
import org.neo4j.kernel.api.exceptions.WriteOnReadOnlyAccessDbException;
import org.neo4j.kernel.database.NamedDatabaseId;
public interface DatabaseReadOnlyChecker {
static DatabaseReadOnlyChecker writable() {
return WritableDatabaseReadOnlyChecker.INSTANCE;
}
static DatabaseReadOnlyChecker readOnly() {
return ReadOnlyDatabaseReadOnlyChecker.INSTANCE;
}
/**
* @return true if database is readonly, false otherwise.
*/
boolean isReadOnly();
/**
* Check if database is a read only and throw exception if its not.
*/
void check();
class Default implements DatabaseReadOnlyChecker {
private volatile long lastUpdated;
private volatile boolean readOnly;
private final ReadOnlyDatabases dbmsChecker;
private final NamedDatabaseId namedDatabaseId;
Default(ReadOnlyDatabases readOnlyDatabases, NamedDatabaseId namedDatabaseId) {
this.lastUpdated = -1;
this.readOnly = false;
this.dbmsChecker = readOnlyDatabases;
this.namedDatabaseId = namedDatabaseId;
}
/**
* Note: this method should *not* be synchronized, for performance reasons.
* There exists a race whereby a database checker will observe an earlier update, but a later readOnly value.
* However, such a race just means that subsequent checks will fall through to {@code dbmsChecker.isReadOnly()} when they did not need to.
* In other words, the race is benign.
*/
@Override
public boolean isReadOnly() {
var globalUpdate = dbmsChecker.updateId();
if (lastUpdated != globalUpdate) {
readOnly = dbmsChecker.isReadOnly(namedDatabaseId.databaseId());
lastUpdated = globalUpdate;
}
return readOnly;
}
@Override
public void check() {
if (isReadOnly()) {
throw new RuntimeException(new WriteOnReadOnlyAccessDbException(namedDatabaseId.name()));
}
}
}
class WritableDatabaseReadOnlyChecker implements DatabaseReadOnlyChecker {
static final WritableDatabaseReadOnlyChecker INSTANCE = new WritableDatabaseReadOnlyChecker();
private WritableDatabaseReadOnlyChecker() {}
@Override
public boolean isReadOnly() {
return false;
}
@Override
public void check() {}
}
class ReadOnlyDatabaseReadOnlyChecker implements DatabaseReadOnlyChecker {
static final ReadOnlyDatabaseReadOnlyChecker INSTANCE = new ReadOnlyDatabaseReadOnlyChecker();
private ReadOnlyDatabaseReadOnlyChecker() {}
@Override
public boolean isReadOnly() {
return true;
}
@Override
public void check() {
throw new RuntimeException(new WriteOnReadOnlyAccessDbException());
}
}
}
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