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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.cassandra.service;
import java.io.File;
import java.io.IOException;
import java.lang.management.ManagementFactory;
import java.lang.management.MemoryPoolMXBean;
import java.net.InetAddress;
import java.net.URL;
import java.net.UnknownHostException;
import java.util.List;
import java.util.concurrent.TimeUnit;
import javax.management.ObjectName;
import javax.management.StandardMBean;
import javax.management.remote.JMXConnectorServer;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.addthis.metrics3.reporter.config.ReporterConfig;
import com.codahale.metrics.Meter;
import com.codahale.metrics.MetricRegistryListener;
import com.codahale.metrics.SharedMetricRegistries;
import com.codahale.metrics.jvm.BufferPoolMetricSet;
import com.codahale.metrics.jvm.FileDescriptorRatioGauge;
import com.codahale.metrics.jvm.GarbageCollectorMetricSet;
import com.codahale.metrics.jvm.MemoryUsageGaugeSet;
import org.apache.cassandra.batchlog.LegacyBatchlogMigrator;
import org.apache.cassandra.concurrent.ScheduledExecutors;
import org.apache.cassandra.config.CFMetaData;
import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.config.Schema;
import org.apache.cassandra.config.SchemaConstants;
import org.apache.cassandra.cql3.QueryProcessor;
import org.apache.cassandra.db.ColumnFamilyStore;
import org.apache.cassandra.db.Keyspace;
import org.apache.cassandra.db.SizeEstimatesRecorder;
import org.apache.cassandra.db.SystemKeyspace;
import org.apache.cassandra.db.WindowsFailedSnapshotTracker;
import org.apache.cassandra.db.commitlog.CommitLog;
import org.apache.cassandra.exceptions.ConfigurationException;
import org.apache.cassandra.exceptions.StartupException;
import org.apache.cassandra.gms.Gossiper;
import org.apache.cassandra.hints.LegacyHintsMigrator;
import org.apache.cassandra.io.FSError;
import org.apache.cassandra.io.sstable.CorruptSSTableException;
import org.apache.cassandra.io.sstable.SSTableHeaderFix;
import org.apache.cassandra.io.util.FileUtils;
import org.apache.cassandra.metrics.CassandraMetricsRegistry;
import org.apache.cassandra.metrics.DefaultNameFactory;
import org.apache.cassandra.metrics.StorageMetrics;
import org.apache.cassandra.schema.LegacySchemaMigrator;
import org.apache.cassandra.security.ThreadAwareSecurityManager;
import org.apache.cassandra.thrift.ThriftServer;
import org.apache.cassandra.tracing.Tracing;
import org.apache.cassandra.utils.FBUtilities;
import org.apache.cassandra.utils.JMXServerUtils;
import org.apache.cassandra.utils.JVMStabilityInspector;
import org.apache.cassandra.utils.MBeanWrapper;
import org.apache.cassandra.utils.Mx4jTool;
import org.apache.cassandra.utils.NativeLibrary;
import org.apache.cassandra.utils.WindowsTimer;
/**
* The CassandraDaemon is an abstraction for a Cassandra daemon
* service, which defines not only a way to activate and deactivate it, but also
* hooks into its lifecycle methods (see {@link #setup()}, {@link #start()},
* {@link #stop()} and {@link #setup()}).
*/
public class CassandraDaemon
{
public static final String MBEAN_NAME = "org.apache.cassandra.db:type=NativeAccess";
private static final Logger logger;
@VisibleForTesting
public static CassandraDaemon getInstanceForTesting()
{
return instance;
}
static {
// Need to register metrics before instrumented appender is created(first access to LoggerFactory).
SharedMetricRegistries.getOrCreate("logback-metrics").addListener(new MetricRegistryListener.Base()
{
@Override
public void onMeterAdded(String metricName, Meter meter)
{
// Given metricName consists of appender name in logback.xml + "." + metric name.
// We first separate appender name
int separator = metricName.lastIndexOf('.');
String appenderName = metricName.substring(0, separator);
String metric = metricName.substring(separator + 1); // remove "."
ObjectName name = DefaultNameFactory.createMetricName(appenderName, metric, null).getMBeanName();
CassandraMetricsRegistry.Metrics.registerMBean(meter, name);
}
});
logger = LoggerFactory.getLogger(CassandraDaemon.class);
}
private void maybeInitJmx()
{
// If the standard com.sun.management.jmxremote.port property has been set
// then the JVM agent will have already started up a default JMX connector
// server. This behaviour is deprecated, but some clients may be relying
// on it, so log a warning and skip setting up the server with the settings
// as configured in cassandra-env.(sh|ps1)
// See: CASSANDRA-11540 & CASSANDRA-11725
if (System.getProperty("com.sun.management.jmxremote.port") != null)
{
logger.warn("JMX settings in cassandra-env.sh have been bypassed as the JMX connector server is " +
"already initialized. Please refer to cassandra-env.(sh|ps1) for JMX configuration info");
return;
}
System.setProperty("java.rmi.server.randomIDs", "true");
// If a remote port has been specified then use that to set up a JMX
// connector server which can be accessed remotely. Otherwise, look
// for the local port property and create a server which is bound
// only to the loopback address. Auth options are applied to both
// remote and local-only servers, but currently SSL is only
// available for remote.
// If neither is remote nor local port is set in cassandra-env.(sh|ps)
// then JMX is effectively disabled.
boolean localOnly = false;
String jmxPort = System.getProperty("cassandra.jmx.remote.port");
if (jmxPort == null)
{
localOnly = true;
jmxPort = System.getProperty("cassandra.jmx.local.port");
}
if (jmxPort == null)
return;
try
{
jmxServer = JMXServerUtils.createJMXServer(Integer.parseInt(jmxPort), localOnly);
if (jmxServer == null)
return;
}
catch (IOException e)
{
exitOrFail(1, e.getMessage(), e.getCause());
}
}
static final CassandraDaemon instance = new CassandraDaemon();
private volatile Server thriftServer;
private volatile NativeTransportService nativeTransportService;
private JMXConnectorServer jmxServer;
private final boolean runManaged;
protected final StartupChecks startupChecks;
private boolean setupCompleted;
public CassandraDaemon()
{
this(false);
}
public CassandraDaemon(boolean runManaged)
{
this.runManaged = runManaged;
this.startupChecks = new StartupChecks().withDefaultTests();
this.setupCompleted = false;
}
/**
* This is a hook for concrete daemons to initialize themselves suitably.
*
* Subclasses should override this to finish the job (listening on ports, etc.)
*/
protected void setup()
{
FileUtils.setFSErrorHandler(new DefaultFSErrorHandler());
// Delete any failed snapshot deletions on Windows - see CASSANDRA-9658
if (FBUtilities.isWindows)
WindowsFailedSnapshotTracker.deleteOldSnapshots();
maybeInitJmx();
Mx4jTool.maybeLoad();
ThreadAwareSecurityManager.install();
logSystemInfo();
NativeLibrary.tryMlockall();
try
{
startupChecks.verify();
}
catch (StartupException e)
{
exitOrFail(e.returnCode, e.getMessage(), e.getCause());
}
try
{
if (SystemKeyspace.snapshotOnVersionChange())
{
SystemKeyspace.migrateDataDirs();
}
}
catch (IOException e)
{
exitOrFail(3, e.getMessage(), e.getCause());
}
// We need to persist this as soon as possible after startup checks.
// This should be the first write to SystemKeyspace (CASSANDRA-11742)
SystemKeyspace.persistLocalMetadata();
Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler()
{
public void uncaughtException(Thread t, Throwable e)
{
StorageMetrics.exceptions.inc();
logger.error("Exception in thread {}", t, e);
Tracing.trace("Exception in thread {}", t, e);
for (Throwable e2 = e; e2 != null; e2 = e2.getCause())
{
// make sure error gets logged exactly once.
if (e2 != e && (e2 instanceof FSError || e2 instanceof CorruptSSTableException))
logger.error("Exception in thread {}", t, e2);
}
JVMStabilityInspector.inspectThrowable(e);
}
});
/*
* Migrate pre-3.0 keyspaces, tables, types, functions, and aggregates, to their new 3.0 storage.
* We don't (and can't) wait for commit log replay here, but we don't need to - all schema changes force
* explicit memtable flushes.
*/
LegacySchemaMigrator.migrate();
// Populate token metadata before flushing, for token-aware sstable partitioning (#6696)
StorageService.instance.populateTokenMetadata();
// load schema from disk
Schema.instance.loadFromDisk();
SSTableHeaderFix.fixNonFrozenUDTIfUpgradeFrom30();
// clean up debris in the rest of the keyspaces
for (String keyspaceName : Schema.instance.getKeyspaces())
{
// Skip system as we've already cleaned it
if (keyspaceName.equals(SchemaConstants.SYSTEM_KEYSPACE_NAME))
continue;
for (CFMetaData cfm : Schema.instance.getTablesAndViews(keyspaceName))
{
try
{
ColumnFamilyStore.scrubDataDirectories(cfm);
}
catch (StartupException e)
{
exitOrFail(e.returnCode, e.getMessage(), e.getCause());
}
}
}
Keyspace.setInitialized();
// initialize keyspaces
for (String keyspaceName : Schema.instance.getKeyspaces())
{
if (logger.isDebugEnabled())
logger.debug("opening keyspace {}", keyspaceName);
// disable auto compaction until gossip settles since disk boundaries may be affected by ring layout
for (ColumnFamilyStore cfs : Keyspace.open(keyspaceName).getColumnFamilyStores())
{
for (ColumnFamilyStore store : cfs.concatWithIndexes())
{
store.disableAutoCompaction();
}
}
}
try
{
loadRowAndKeyCacheAsync().get();
}
catch (Throwable t)
{
JVMStabilityInspector.inspectThrowable(t);
logger.warn("Error loading key or row cache", t);
}
try
{
GCInspector.register();
}
catch (Throwable t)
{
JVMStabilityInspector.inspectThrowable(t);
logger.warn("Unable to start GCInspector (currently only supported on the Sun JVM)");
}
// Replay any CommitLogSegments found on disk
try
{
CommitLog.instance.recoverSegmentsOnDisk();
}
catch (IOException e)
{
throw new RuntimeException(e);
}
// Re-populate token metadata after commit log recover (new peers might be loaded onto system keyspace #10293)
StorageService.instance.populateTokenMetadata();
// migrate any legacy (pre-3.0) hints from system.hints table into the new store
new LegacyHintsMigrator(DatabaseDescriptor.getHintsDirectory(), DatabaseDescriptor.getMaxHintsFileSize()).migrate();
// migrate any legacy (pre-3.0) batch entries from system.batchlog to system.batches (new table format)
LegacyBatchlogMigrator.migrate();
SystemKeyspace.finishStartup();
// Clean up system.size_estimates entries left lying around from missed keyspace drops (CASSANDRA-14905)
StorageService.instance.cleanupSizeEstimates();
// schedule periodic dumps of table size estimates into SystemKeyspace.SIZE_ESTIMATES_CF
// set cassandra.size_recorder_interval to 0 to disable
int sizeRecorderInterval = Integer.getInteger("cassandra.size_recorder_interval", 5 * 60);
if (sizeRecorderInterval > 0)
ScheduledExecutors.optionalTasks.scheduleWithFixedDelay(SizeEstimatesRecorder.instance, 30, sizeRecorderInterval, TimeUnit.SECONDS);
// Prepared statements
QueryProcessor.preloadPreparedStatement();
// Metrics
String metricsReporterConfigFile = System.getProperty("cassandra.metricsReporterConfigFile");
if (metricsReporterConfigFile != null)
{
logger.info("Trying to load metrics-reporter-config from file: {}", metricsReporterConfigFile);
try
{
// enable metrics provided by metrics-jvm.jar
CassandraMetricsRegistry.Metrics.register("jvm.buffers", new BufferPoolMetricSet(ManagementFactory.getPlatformMBeanServer()));
CassandraMetricsRegistry.Metrics.register("jvm.gc", new GarbageCollectorMetricSet());
CassandraMetricsRegistry.Metrics.register("jvm.memory", new MemoryUsageGaugeSet());
CassandraMetricsRegistry.Metrics.register("jvm.fd.usage", new FileDescriptorRatioGauge());
// initialize metrics-reporter-config from yaml file
URL resource = CassandraDaemon.class.getClassLoader().getResource(metricsReporterConfigFile);
if (resource == null)
{
logger.warn("Failed to load metrics-reporter-config, file does not exist: {}", metricsReporterConfigFile);
}
else
{
String reportFileLocation = resource.getFile();
ReporterConfig.loadFromFile(reportFileLocation).enableAll(CassandraMetricsRegistry.Metrics);
}
}
catch (Exception e)
{
logger.warn("Failed to load metrics-reporter-config, metric sinks will not be activated", e);
}
}
// start server internals
StorageService.instance.registerDaemon(this);
try
{
StorageService.instance.initServer();
}
catch (ConfigurationException e)
{
System.err.println(e.getMessage() + "\nFatal configuration error; unable to start server. See log for stacktrace.");
exitOrFail(1, "Fatal configuration error", e);
}
// Because we are writing to the system_distributed keyspace, this should happen after that is created, which
// happens in StorageService.instance.initServer()
Runnable viewRebuild = () -> {
for (Keyspace keyspace : Keyspace.all())
{
keyspace.viewManager.buildAllViews();
}
logger.debug("Completed submission of build tasks for any materialized views defined at startup");
};
ScheduledExecutors.optionalTasks.schedule(viewRebuild, StorageService.RING_DELAY, TimeUnit.MILLISECONDS);
if (!FBUtilities.getBroadcastAddress().equals(InetAddress.getLoopbackAddress()))
Gossiper.waitToSettle();
// re-enable auto-compaction after gossip is settled, so correct disk boundaries are used
for (Keyspace keyspace : Keyspace.all())
{
for (ColumnFamilyStore cfs : keyspace.getColumnFamilyStores())
{
for (final ColumnFamilyStore store : cfs.concatWithIndexes())
{
store.reload(); //reload CFs in case there was a change of disk boundaries
if (store.getCompactionStrategyManager().shouldBeEnabled())
{
store.enableAutoCompaction();
}
}
}
}
// schedule periodic background compaction task submission. this is simply a backstop against compactions stalling
// due to scheduling errors or race conditions
ScheduledExecutors.optionalTasks.scheduleWithFixedDelay(ColumnFamilyStore.getBackgroundCompactionTaskSubmitter(), 5, 1, TimeUnit.MINUTES);
initializeClientTransports();
completeSetup();
}
public synchronized void initializeClientTransports()
{
// Thrift
InetAddress rpcAddr = DatabaseDescriptor.getRpcAddress();
int rpcPort = DatabaseDescriptor.getRpcPort();
int listenBacklog = DatabaseDescriptor.getRpcListenBacklog();
if (thriftServer == null)
thriftServer = new ThriftServer(rpcAddr, rpcPort, listenBacklog);
// Native transport
if (nativeTransportService == null)
nativeTransportService = new NativeTransportService();
}
/*
* Asynchronously load the row and key cache in one off threads and return a compound future of the result.
* Error handling is pushed into the cache load since cache loads are allowed to fail and are handled by logging.
*/
private ListenableFuture loadRowAndKeyCacheAsync()
{
final ListenableFuture keyCacheLoad = CacheService.instance.keyCache.loadSavedAsync();
final ListenableFuture rowCacheLoad = CacheService.instance.rowCache.loadSavedAsync();
@SuppressWarnings("unchecked")
ListenableFuture> retval = Futures.successfulAsList(keyCacheLoad, rowCacheLoad);
return retval;
}
@VisibleForTesting
public void completeSetup()
{
setupCompleted = true;
}
public boolean setupCompleted()
{
return setupCompleted;
}
private void logSystemInfo()
{
if (logger.isInfoEnabled())
{
try
{
logger.info("Hostname: {}", InetAddress.getLocalHost().getHostName());
}
catch (UnknownHostException e1)
{
logger.info("Could not resolve local host");
}
logger.info("JVM vendor/version: {}/{}", System.getProperty("java.vm.name"), System.getProperty("java.version"));
logger.info("Heap size: {}/{}",
FBUtilities.prettyPrintMemory(Runtime.getRuntime().totalMemory()),
FBUtilities.prettyPrintMemory(Runtime.getRuntime().maxMemory()));
for(MemoryPoolMXBean pool: ManagementFactory.getMemoryPoolMXBeans())
logger.info("{} {}: {}", pool.getName(), pool.getType(), pool.getPeakUsage());
logger.info("Classpath: {}", System.getProperty("java.class.path"));
logger.info("JVM Arguments: {}", ManagementFactory.getRuntimeMXBean().getInputArguments());
}
}
/**
* Initialize the Cassandra Daemon based on the given Commons
* Daemon-specific arguments. To clarify, this is a hook for JSVC.
*
* @param arguments
* the arguments passed in from JSVC
* @throws IOException
*/
public void init(String[] arguments) throws IOException
{
setup();
}
/**
* Start the Cassandra Daemon, assuming that it has already been
* initialized via {@link #init(String[])}
*
* Hook for JSVC
*/
public void start()
{
// check to see if transports may start else return without starting. This is needed when in survey mode or
// when bootstrap has not completed.
try
{
validateTransportsCanStart();
}
catch (IllegalStateException isx)
{
// If there are any errors, we just log and return in this case
logger.info(isx.getMessage());
return;
}
startClientTransports();
}
private void startClientTransports()
{
String nativeFlag = System.getProperty("cassandra.start_native_transport");
if ((nativeFlag != null && Boolean.parseBoolean(nativeFlag)) || (nativeFlag == null && DatabaseDescriptor.startNativeTransport()))
{
startNativeTransport();
StorageService.instance.setRpcReady(true);
}
else
logger.info("Not starting native transport as requested. Use JMX (StorageService->startNativeTransport()) or nodetool (enablebinary) to start it");
String rpcFlag = System.getProperty("cassandra.start_rpc");
if ((rpcFlag != null && Boolean.parseBoolean(rpcFlag)) || (rpcFlag == null && DatabaseDescriptor.startRpc()))
startThriftServer();
else
logger.info("Not starting RPC server as requested. Use JMX (StorageService->startRPCServer()) or nodetool (enablethrift) to start it");
}
/**
* Stop the daemon, ideally in an idempotent manner.
*
* Hook for JSVC / Procrun
*/
public void stop()
{
// On linux, this doesn't entirely shut down Cassandra, just the RPC server.
// jsvc takes care of taking the rest down
logger.info("Cassandra shutting down...");
destroyClientTransports();
StorageService.instance.setRpcReady(false);
// On windows, we need to stop the entire system as prunsrv doesn't have the jsvc hooks
// We rely on the shutdown hook to drain the node
if (FBUtilities.isWindows)
System.exit(0);
if (jmxServer != null)
{
try
{
jmxServer.stop();
}
catch (IOException e)
{
logger.error("Error shutting down local JMX server: ", e);
}
}
}
@VisibleForTesting
public void destroyClientTransports()
{
stopThriftServer();
stopNativeTransport();
if (nativeTransportService != null)
nativeTransportService.destroy();
}
/**
* Clean up all resources obtained during the lifetime of the daemon. This
* is a hook for JSVC.
*/
public void destroy()
{}
/**
* A convenience method to initialize and start the daemon in one shot.
*/
public void activate()
{
// Do not put any references to DatabaseDescriptor above the forceStaticInitialization call.
try
{
applyConfig();
MBeanWrapper.instance.registerMBean(new StandardMBean(new NativeAccess(), NativeAccessMBean.class), MBEAN_NAME, MBeanWrapper.OnException.LOG);
if (FBUtilities.isWindows)
{
// We need to adjust the system timer on windows from the default 15ms down to the minimum of 1ms as this
// impacts timer intervals, thread scheduling, driver interrupts, etc.
WindowsTimer.startTimerPeriod(DatabaseDescriptor.getWindowsTimerInterval());
}
setup();
String pidFile = System.getProperty("cassandra-pidfile");
if (pidFile != null)
{
new File(pidFile).deleteOnExit();
}
if (System.getProperty("cassandra-foreground") == null)
{
System.out.close();
System.err.close();
}
start();
logger.info("Startup complete");
}
catch (Throwable e)
{
boolean logStackTrace =
e instanceof ConfigurationException ? ((ConfigurationException)e).logStackTrace : true;
System.out.println("Exception (" + e.getClass().getName() + ") encountered during startup: " + e.getMessage());
if (logStackTrace)
{
if (runManaged)
logger.error("Exception encountered during startup", e);
// try to warn user on stdout too, if we haven't already detached
e.printStackTrace();
exitOrFail(3, "Exception encountered during startup", e);
}
else
{
if (runManaged)
logger.error("Exception encountered during startup: {}", e.getMessage());
// try to warn user on stdout too, if we haven't already detached
System.err.println(e.getMessage());
exitOrFail(3, "Exception encountered during startup: " + e.getMessage());
}
}
}
public void applyConfig()
{
DatabaseDescriptor.daemonInitialization();
}
public void validateTransportsCanStart()
{
// We only start transports if bootstrap has completed and we're not in survey mode, OR if we are in
// survey mode and streaming has completed but we're not using auth.
// OR if we have not joined the ring yet.
if (StorageService.instance.hasJoined())
{
if (StorageService.instance.isSurveyMode())
{
if (StorageService.instance.isBootstrapMode() || DatabaseDescriptor.getAuthenticator().requireAuthentication())
{
throw new IllegalStateException("Not starting client transports in write_survey mode as it's bootstrapping or " +
"auth is enabled");
}
}
else
{
if (!SystemKeyspace.bootstrapComplete())
{
throw new IllegalStateException("Node is not yet bootstrapped completely. Use nodetool to check bootstrap" +
" state and resume. For more, see `nodetool help bootstrap`");
}
}
}
}
public void startNativeTransport()
{
validateTransportsCanStart();
if (nativeTransportService == null)
throw new IllegalStateException("setup() must be called first for CassandraDaemon");
nativeTransportService.start();
}
public void stopNativeTransport()
{
if (nativeTransportService != null)
{
nativeTransportService.stop();
}
}
public boolean isNativeTransportRunning()
{
return nativeTransportService != null && nativeTransportService.isRunning();
}
public void startThriftServer()
{
validateTransportsCanStart();
if (thriftServer == null)
throw new IllegalStateException("setup() must be called first for CassandraDaemon");
thriftServer.start();
}
public void stopThriftServer()
{
if (thriftServer != null)
{
thriftServer.stop();
}
}
public boolean isThriftServerRunning()
{
return thriftServer != null && thriftServer.isRunning();
}
public int getMaxNativeProtocolVersion()
{
return nativeTransportService.getMaxProtocolVersion();
}
public void refreshMaxNativeProtocolVersion()
{
if (nativeTransportService != null)
nativeTransportService.refreshMaxNegotiableProtocolVersion();
}
/**
* A convenience method to stop and destroy the daemon in one shot.
*/
public void deactivate()
{
stop();
destroy();
// completely shut down cassandra
if(!runManaged)
{
System.exit(0);
}
}
public static void stop(String[] args)
{
instance.deactivate();
}
public static void main(String[] args)
{
instance.activate();
}
private void exitOrFail(int code, String message)
{
exitOrFail(code, message, null);
}
private void exitOrFail(int code, String message, Throwable cause)
{
if (runManaged)
{
RuntimeException t = cause!=null ? new RuntimeException(message, cause) : new RuntimeException(message);
throw t;
}
else
{
logger.error(message, cause);
System.exit(code);
}
}
static class NativeAccess implements NativeAccessMBean
{
public boolean isAvailable()
{
return NativeLibrary.isAvailable();
}
public boolean isMemoryLockable()
{
return NativeLibrary.jnaMemoryLockable();
}
}
public interface Server
{
/**
* Start the server.
* This method shoud be able to restart a server stopped through stop().
* Should throw a RuntimeException if the server cannot be started
*/
public void start();
/**
* Stop the server.
* This method should be able to stop server started through start().
* Should throw a RuntimeException if the server cannot be stopped
*/
public void stop();
/**
* Returns whether the server is currently running.
*/
public boolean isRunning();
}
}