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JDBC Driver for the Firebird RDBMS
/*
* Firebird Open Source J2ee connector - jdbc driver
*
* Distributable under LGPL license.
* You may obtain a copy of the License at http://www.gnu.org/copyleft/lgpl.html
*
* 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
* LGPL License for more details.
*
* This file was created by members of the firebird development team.
* All individual contributions remain the Copyright (C) of those
* individuals. Contributors to this file are either listed here or
* can be obtained from a CVS history command.
*
* All rights reserved.
*/
package org.firebirdsql.pool;
import org.firebirdsql.jdbc.FBSQLException;
import org.firebirdsql.logging.Logger;
import org.firebirdsql.util.SQLExceptionChainBuilder;
import java.sql.SQLException;
import java.util.*;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
/**
* Implementation of free connection queue.
*
* @author Roman Rokytskyy
* @author Mark Rotteveel
*/
final class PooledConnectionQueue {
private static final boolean LOG_DEBUG_INFO = PoolDebugConfiguration.LOG_DEBUG_INFO;
private static final boolean SHOW_STACK_ON_BLOCK = PoolDebugConfiguration.SHOW_TRACE;
private static final boolean SHOW_STACK_ON_ALLOCATION = PoolDebugConfiguration.SHOW_TRACE;
private final PooledConnectionManager connectionManager;
private final Logger logger;
private final ConnectionPoolConfiguration configuration;
private final Object key;
private final String queueName;
private final int blockingTimeout;
private final Object addConnectionMutex = new Object();
private IdleRemover idleRemover;
private final BlockingQueue idleConnections;
private final Set allConnections;
private final Set workingConnections;
private final Set workingConnectionsToClose;
private final AtomicReference queueState = new AtomicReference(QueueState.NEW);
/**
* Create instance of this queue for the specified user name and password.
*
* @param connectionManager
* instance of {@link PooledConnectionManager}.
* @param logger
* instance of {@link Logger}.
* @param configuration
* instance of {@link ConnectionPoolConfiguration}.
* @param queueName
* name of this queue.
* @param key
* Key used for this instance
*/
public PooledConnectionQueue(PooledConnectionManager connectionManager,
Logger logger, ConnectionPoolConfiguration configuration,
String queueName, Object key) {
this.connectionManager = connectionManager;
this.logger = logger;
this.configuration = configuration;
this.queueName = queueName;
blockingTimeout = configuration.getBlockingTimeout();
this.key = key;
// NOTE: We are always creating an unbounded queue as the max pool size could change at runtime
idleConnections = new LinkedBlockingQueue();
final int initialSize = Math.max(16, configuration.getMaxPoolSize());
allConnections = Collections.synchronizedSet(new HashSet(initialSize));
workingConnections = Collections.synchronizedSet(new HashSet(initialSize));
workingConnectionsToClose = Collections.synchronizedSet(new HashSet(initialSize));
}
/**
* Get size of this queue. This method can be used to check how many free connections are left.
*
* @return size of this queue.
*/
public int size() {
return idleConnections.size();
}
/**
* Get total number of physical connections opened to the database.
*
* @return total number of physical connections opened to the database.
*/
public int totalSize() {
return allConnections.size();
}
/**
* Get number of working connections.
*
* @return number for working connections.
*/
public int workingSize() {
return workingConnections.size();
}
/**
* Start this queue.
*
* @throws SQLException
* if initial number of connections
* could not be created.
*/
public void start() throws SQLException {
if (!queueState.compareAndSet(QueueState.NEW, QueueState.STARTED)) return;
for (int i = 0; i < configuration.getMinPoolSize(); i++) {
addConnection();
}
idleRemover = new IdleRemover();
Thread t = new Thread(idleRemover, "Pool " + queueName + " idleRemover");
t.setDaemon(true);
t.start();
}
/**
* Restart this queue.
*/
public void restart() throws SQLException {
if (!queueState.compareAndSet(QueueState.STARTED, QueueState.RESTARTING)) {
// NOTE: Minor chance of a race condition here so it could potentially show that the state is STARTED
final QueueState currentState = queueState.get();
throw new SQLException("Queue " + queueName + " cannot be restarted, current state is: " + currentState);
}
try {
// Move current idle connections to list for removal
final List connectionsToClose = new ArrayList(size());
idleConnections.drainTo(connectionsToClose);
// flag working connections for deallocation when returned to the queue.
workingConnectionsToClose.addAll(workingConnections);
// close all free connections
for (PooledObject connection : connectionsToClose) {
try {
if (connection.isValid()) {
connection.deallocate();
}
} catch (Exception ex) {
if (logger != null) {
logger.warn("Could not close connection.", ex);
}
} finally {
physicalConnectionDeallocated(connection);
}
}
//Create enough connections to restore the queue to MinPoolSize.
while (totalSize() < configuration.getMinPoolSize()) {
if (queueState.get() != QueueState.RESTARTING) {
break;
}
try {
addConnection();
} catch (Exception e) {
if (logger != null) {
logger.warn("Could not add connection.", e);
}
}
}
} finally {
if (!queueState.compareAndSet(QueueState.RESTARTING, QueueState.STARTED)
&& queueState.get() == QueueState.RETRY_SHUTDOWN) {
// Shutdown of the queue was signalled while we were restarting, shutdown now
shutdown();
}
}
}
/**
* Shutdown this queue.
*/
public void shutdown() throws SQLException {
final QueueState previousState = queueState.getAndSet(QueueState.SHUTDOWN);
switch (previousState) {
case SHUTDOWN:
return;
case RESTARTING:
if (queueState.compareAndSet(QueueState.SHUTDOWN, QueueState.RETRY_SHUTDOWN)) {
return;
} else if (!queueState.compareAndSet(QueueState.STARTED, QueueState.SHUTDOWN)) {
// Restart has apparently completed, but is not in state STARTED
throw new SQLException("Current queue state prevented shutdown. Please retry.");
}
}
if (idleRemover != null)
idleRemover.stop();
idleRemover = null;
/* Synchronizing on addConnectionMutex to ensure that no add or create operation in progress interferes.
*/
synchronized (addConnectionMutex) {
idleConnections.clear();
workingConnections.clear();
workingConnectionsToClose.clear();
// close all current connections.
for (PooledObject item : allConnections) {
try {
if (item.isValid())
item.deallocate();
} catch (Exception ex) {
if (logger != null) {
logger.warn("Could not deallocate connection.", ex);
}
}
}
allConnections.clear();
}
}
/**
* Check if {@link #take()} method can keep blocking.
*
* @param startTime
* time when the method was entered.
* @return true if method can keep blocking.
*/
private boolean keepBlocking(long startTime) {
return System.currentTimeMillis() - startTime < blockingTimeout;
}
/**
* Destroy connection and restore the balance of connections in the pool.
*
* @param connection
* connection to destroy
*/
public void destroyConnection(PooledObject connection) {
try {
connection.deallocate();
} finally {
physicalConnectionDeallocated(connection);
}
}
/**
* Notify queue that a physical connection was deallocated.
*
* @param connection
* connection that was deallocated.
*/
public void physicalConnectionDeallocated(PooledObject connection) {
allConnections.remove(connection);
workingConnections.remove(connection);
}
/**
* Put connection to this queue.
*
* @param connection
* free pooled connection.
* @throws SQLException
* if connection cannot be added to this
* queue.
*/
public void put(PooledObject connection) throws SQLException {
final QueueState currentState = queueState.get();
if (currentState == QueueState.NEW) {
throw new SQLException("Queue has not been started yet");
} else if (!currentState.isAllowPut()) {
destroyConnection(connection);
if (LOG_DEBUG_INFO && logger != null) {
logger.debug("Thread " + Thread.currentThread().getName() + " released connection while pool was in state ." + currentState);
}
return;
}
if (configuration.isPooling()) {
connection.setInPool(true);
if (workingConnectionsToClose.remove(connection)) {
destroyConnection(connection);
addConnection();
} else if (!idleConnections.offer(connection)) {
// Maximum capacity reached
destroyConnection(connection);
} else {
workingConnections.remove(connection);
}
} else {
// deallocate connection if pooling is not enabled.
destroyConnection(connection);
}
if (LOG_DEBUG_INFO && logger != null) {
logger.debug("Thread " + Thread.currentThread().getName() + " released connection.");
}
}
/**
* Take pooled connection from this queue. This method will block
* until free and valid connection is available.
*
* @return free instance of {@link FBPooledConnection}.
* @throws SQLException
* if no free connection was available and
* waiting thread was interruped while waiting for a new free
* connection.
*/
public PooledObject take() throws SQLException {
final QueueState currentState = queueState.get();
if (!currentState.isAllowTake()) {
throw new SQLException("Current queue state " + currentState + " does not allow take() on connection queue");
}
final long startTime = System.currentTimeMillis();
if (LOG_DEBUG_INFO && logger != null) {
logger.debug("Thread " + Thread.currentThread().getName() + " wants to take connection.");
}
final SQLExceptionChainBuilder pendingExceptions = new SQLExceptionChainBuilder();
PooledObject result = null;
try {
do {
if (idleConnections.isEmpty()) {
// Queue empty, Attempt to create a new connection directly
try {
result = createPooledConnection();
} catch (SQLException sqlex) {
if (logger != null) {
logger.warn("Could not create connection." + sqlex.getMessage());
}
if (!pendingExceptions.hasException()) {
pendingExceptions.append(sqlex);
} else if (pendingExceptions.getException().getErrorCode() != sqlex.getErrorCode()) {
pendingExceptions.append(sqlex);
}
}
} // intentionally no else here!
if (result == null) {
// Try to obtain connection from pool
result = idleConnections.poll(configuration.getRetryInterval(), TimeUnit.MILLISECONDS);
}
if (result != null) {
// Retrieved from pool
if (logger != null) {
logger.info("Obtained connection. Thread " + Thread.currentThread().getName());
}
result.setInPool(false);
workingConnections.add(result);
break;
}
if (!keepBlocking(startTime)) {
final String message = "Could not obtain connection during blocking timeout (" + blockingTimeout + " ms)";
FBSQLException ex = new FBSQLException(message, FBSQLException.SQL_STATE_CONNECTION_FAILURE);
if (pendingExceptions.hasException()) {
ex.setNextException(pendingExceptions.getException());
}
throw ex;
}
String message = "Pool " + queueName + " is empty and will block here. Thread " + Thread.currentThread().getName();
if (logger != null) {
if (SHOW_STACK_ON_BLOCK) {
logger.warn(message, new Exception());
} else {
logger.warn(message);
}
}
} while (true);
} catch (InterruptedException iex) {
throw new SQLException("No free connection was available and waiting thread was interrupted.");
}
if (LOG_DEBUG_INFO && logger != null) {
final String message = "Thread " + Thread.currentThread().getName() + " got connection.";
if (SHOW_STACK_ON_ALLOCATION) {
logger.debug(message, new Exception());
} else {
logger.debug(message);
}
}
return result;
}
/**
* Opens new connection to database and adds it to the pool.
*
* @return true if new physical connection was created,
* otherwise false.
* @throws SQLException
* if new connection cannot be opened.
*/
private boolean addConnection() throws SQLException {
if (LOG_DEBUG_INFO && logger != null) {
logger.debug("Trying to create connection, total connections " + allConnections.size()
+ ", max allowed " + configuration.getMaxPoolSize());
}
if (idleConnections.remainingCapacity() == 0) {
if (LOG_DEBUG_INFO && logger != null) {
logger.debug("Unable to add more connections, maximum capacity reached.");
}
return false;
}
synchronized (addConnectionMutex) {
if (!queueState.get().isAllowAdd()) return false;
PooledObject pooledConnection = createPooledConnection();
if (pooledConnection == null) {
if (LOG_DEBUG_INFO && logger != null) {
logger.debug("Unable to add more connections, maximum capacity reached.");
}
return false;
}
if (LOG_DEBUG_INFO && logger != null) {
logger.debug("Thread " + Thread.currentThread().getName() + " created connection.");
}
if (idleConnections.offer(pooledConnection)) {
return true;
}
/* We cannot add the connection to the pool, we will destroy it again
* NOTE: In the current implementation idleConnections is unbounded so we should never get here
*/
destroyConnection(pooledConnection);
if (LOG_DEBUG_INFO && logger != null) {
logger.debug("Thread " + Thread.currentThread().getName() + " forced to abandon created connection, capacity reached.");
}
return false;
}
}
/**
* Creates a new pooledConnection without adding it to the idleConnections queue.
*
* @return A new PooledConnection or null when the maximum pool capacity was already reached or allocating new connections is currently not allowed.
* @throws SQLException
* For errors allocating the exception.
*/
private PooledObject createPooledConnection() throws SQLException {
synchronized (addConnectionMutex) {
if (!queueState.get().isAllowAdd()) return null;
boolean maximumCapacityReached =
configuration.isPooling() &&
configuration.getMaxPoolSize() != 0 &&
configuration.getMaxPoolSize() <= totalSize();
if (maximumCapacityReached) {
if (LOG_DEBUG_INFO && logger != null) {
logger.debug("Unable to add more connections, maximum capacity reached.");
}
return null;
}
PooledObject pooledConnection = connectionManager.allocateConnection(key, this);
allConnections.add(pooledConnection);
if (LOG_DEBUG_INFO && logger != null) {
logger.debug("Thread " + Thread.currentThread().getName() + " created connection.");
}
return pooledConnection;
}
}
/**
* Release first connection in the queue if it was idle longer than idle
* timeout interval.
*
* @return true if method removed idle connection, otherwise
* false
* @throws SQLException
* if exception happened when releasing the connection.
*/
private boolean releaseNextIdleConnection() throws SQLException {
if (totalSize() <= configuration.getMinPoolSize())
return false;
/* Initial check without removing object from idleConnections queue.
* This is to prevent too much unnecessary removal of items from head and adding them to to the back
* of the queue which might lead to too many idle connections older than maxIdleTime at the end
* of the queue while younger items exist at the head of the queue.
*/
final PooledObject initialCandidate = idleConnections.peek();
if (initialCandidate == null
|| initialCandidate.getInstantInPool() >= System.currentTimeMillis() - configuration.getMaxIdleTime()) {
// No candidate or initial candidate is too recent, abandon further checks
return false;
}
// We temporarily remove the connection from the pool to make further checks
// We repeat all checks as in the meantime the previous (peeked) candidate may have been obtained from the pool
final PooledObject candidate = idleConnections.poll();
if (candidate == null) {
return false;
}
final long lastUsageTime = candidate.getInstantInPool();
if (lastUsageTime == PooledObject.INSTANT_IN_USE && idleConnections.offer(candidate)) {
return false;
} else {
final long idleTime = System.currentTimeMillis() - lastUsageTime;
if (idleTime < configuration.getMaxIdleTime() && idleConnections.offer(candidate)) {
return false;
}
if (logger != null && logger.isDebugEnabled()) {
logger.debug(String.format("Going to remove connection with idleTime %d (max is %d)%n", idleTime, configuration.getMaxIdleTime()));
}
}
destroyConnection(candidate);
if (totalSize() < configuration.getMinPoolSize()) {
// We assume our current action caused the pool to shrink below the minimum size, so we add one
addConnection();
}
return true;
}
/**
* Implementation of {@link Runnable} interface responsible for removing
* idle connections.
*/
private class IdleRemover implements Runnable {
private volatile boolean running;
public IdleRemover() {
running = true;
}
public void stop() {
running = false;
}
public void run() {
while (running) {
try {
int releasedInIteration = 0;
while (releaseNextIdleConnection()) {
releasedInIteration++;
}
if (logger != null && releasedInIteration > 0) {
logger.trace("IdleRemover for " + queueName + " released " + releasedInIteration + " connections");
}
} catch (SQLException ex) {
// do nothing, we hardly can handle this situation
}
try {
final int idleTimeout = configuration.getMaxIdleTime();
Thread.sleep(Math.max(500, idleTimeout / 4));
} catch (InterruptedException ex) {
// do nothing
}
}
}
}
private enum QueueState {
NEW(false, false, false),
STARTED(true, true, true),
RESTARTING(true, true, true),
RETRY_SHUTDOWN(false, false, false),
SHUTDOWN(false, false, false);
private final boolean allowPut;
private final boolean allowTake;
private final boolean allowAdd;
private QueueState(boolean allowPut, boolean allowTake, boolean allowAdd) {
this.allowPut = allowPut;
this.allowTake = allowTake;
this.allowAdd = allowAdd;
}
public boolean isAllowPut() {
return allowPut;
}
public boolean isAllowTake() {
return allowTake;
}
public boolean isAllowAdd() {
return allowAdd;
}
}
}