/*-
* See the file LICENSE for redistribution information.
*
* Copyright (c) 2000, 2015 Oracle and/or its affiliates. All rights reserved.
*
*/
package com.sleepycat.collections;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.List;
import java.util.WeakHashMap;
import com.sleepycat.compat.DbCompat;
import com.sleepycat.db.Cursor;
import com.sleepycat.db.CursorConfig;
import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.Environment;
import com.sleepycat.db.EnvironmentConfig;
import com.sleepycat.db.LockMode;
import com.sleepycat.db.Transaction;
import com.sleepycat.db.TransactionConfig;
import com.sleepycat.util.RuntimeExceptionWrapper;
/**
* Provides access to the current transaction for the current thread within the
* context of a Berkeley DB environment. This class provides explicit
* transaction control beyond that provided by the {@link TransactionRunner}
* class. However, both methods of transaction control manage per-thread
* transactions.
*
* @author Mark Hayes
*/
public class CurrentTransaction {
/* For internal use, this class doubles as an Environment wrapper. */
private static WeakHashMap<Environment, CurrentTransaction> envMap =
new WeakHashMap<Environment, CurrentTransaction>();
private LockMode writeLockMode;
private boolean cdbMode;
private boolean txnMode;
private boolean lockingMode;
private ThreadLocal localTrans = new ThreadLocal();
private ThreadLocal localCdbCursors;
/*
* Use a WeakReference to the Environment to avoid pinning the environment
* in the envMap. The WeakHashMap envMap uses the Environment as a weak
* key, but this won't prevent GC of the Environment if the map's value has
* a hard reference to the Environment. [#15444]
*/
private WeakReference<Environment> envRef;
/**
* Gets the CurrentTransaction accessor for a specified Berkeley DB
* environment. This method always returns the same reference when called
* more than once with the same environment parameter.
*
* @param env is an open Berkeley DB environment.
*
* @return the CurrentTransaction accessor for the given environment, or
* null if the environment is not transactional.
*/
public static CurrentTransaction getInstance(Environment env) {
CurrentTransaction currentTxn = getInstanceInternal(env);
return currentTxn.isTxnMode() ? currentTxn : null;
}
/**
* Gets the CurrentTransaction accessor for a specified Berkeley DB
* environment. Unlike getInstance(), this method never returns null.
*
* @param env is an open Berkeley DB environment.
*/
static CurrentTransaction getInstanceInternal(Environment env) {
synchronized (envMap) {
CurrentTransaction ct = envMap.get(env);
if (ct == null) {
ct = new CurrentTransaction(env);
envMap.put(env, ct);
}
return ct;
}
}
private CurrentTransaction(Environment env) {
envRef = new WeakReference<Environment>(env);
try {
EnvironmentConfig config = env.getConfig();
txnMode = config.getTransactional();
lockingMode = DbCompat.getInitializeLocking(config);
if (txnMode || lockingMode) {
writeLockMode = LockMode.RMW;
} else {
writeLockMode = LockMode.DEFAULT;
}
cdbMode = DbCompat.getInitializeCDB(config);
if (cdbMode) {
localCdbCursors = new ThreadLocal();
}
} catch (DatabaseException e) {
throw RuntimeExceptionWrapper.wrapIfNeeded(e);
}
}
/**
* Returns whether environment is configured for locking.
*/
final boolean isLockingMode() {
return lockingMode;
}
/**
* Returns whether this is a transactional environment.
*/
final boolean isTxnMode() {
return txnMode;
}
/**
* Returns whether this is a Concurrent Data Store environment.
*/
final boolean isCdbMode() {
return cdbMode;
}
/**
* Return the LockMode.RMW or null, depending on whether locking is
* enabled. LockMode.RMW will cause an error if passed when locking
* is not enabled. Locking is enabled if locking or transactions were
* specified for this environment.
*/
final LockMode getWriteLockMode() {
return writeLockMode;
}
/**
* Returns the underlying Berkeley DB environment.
*/
public final Environment getEnvironment() {
return envRef.get();
}
/**
* Returns the transaction associated with the current thread for this
* environment, or null if no transaction is active.
*/
public final Transaction getTransaction() {
Trans trans = (Trans) localTrans.get();
return (trans != null) ? trans.txn : null;
}
/**
* Returns whether auto-commit may be performed by the collections API.
* True is returned if no collections API transaction is currently active,
* and no XA transaction is currently active.
*/
boolean isAutoCommitAllowed()
throws DatabaseException {
return getTransaction() == null &&
DbCompat.getThreadTransaction(getEnvironment()) == null;
}
/**
* Begins a new transaction for this environment and associates it with
* the current thread. If a transaction is already active for this
* environment and thread, a nested transaction will be created.
*
* @param config the transaction configuration used for calling
* {@link Environment#beginTransaction}, or null to use the default
* configuration.
*
* @return the new transaction.
*
*
* @throws DatabaseException if the transaction cannot be started, in which
* case any existing transaction is not affected.
*
* @throws IllegalStateException if a transaction is already active and
* nested transactions are not supported by the environment.
*/
public final Transaction beginTransaction(TransactionConfig config)
throws DatabaseException {
Environment env = getEnvironment();
Trans trans = (Trans) localTrans.get();
if (trans != null) {
if (trans.txn != null) {
if (!DbCompat.NESTED_TRANSACTIONS) {
throw new IllegalStateException
("Nested transactions are not supported");
}
Transaction parentTxn = trans.txn;
trans = new Trans(trans, config);
trans.txn = env.beginTransaction(parentTxn, config);
localTrans.set(trans);
} else {
trans.txn = env.beginTransaction(null, config);
trans.config = config;
}
} else {
trans = new Trans(null, config);
trans.txn = env.beginTransaction(null, config);
localTrans.set(trans);
}
return trans.txn;
}
/**
* Commits the transaction that is active for the current thread for this
* environment and makes the parent transaction (if any) the current
* transaction.
*
* @return the parent transaction or null if the committed transaction was
* not nested.
*
*
* @throws DatabaseException if an error occurs committing the transaction.
* The transaction will still be closed and the parent transaction will
* become the current transaction.
*
* @throws IllegalStateException if no transaction is active for the
* current thread for this environment.
*/
public final Transaction commitTransaction()
throws DatabaseException, IllegalStateException {
Trans trans = (Trans) localTrans.get();
if (trans != null && trans.txn != null) {
Transaction parent = closeTxn(trans);
trans.txn.commit();
return parent;
} else {
throw new IllegalStateException("No transaction is active");
}
}
/**
* Aborts the transaction that is active for the current thread for this
* environment and makes the parent transaction (if any) the current
* transaction.
*
* @return the parent transaction or null if the aborted transaction was
* not nested.
*
*
* @throws DatabaseException if an error occurs aborting the transaction.
* The transaction will still be closed and the parent transaction will
* become the current transaction.
*
* @throws IllegalStateException if no transaction is active for the
* current thread for this environment.
*/
public final Transaction abortTransaction()
throws DatabaseException, IllegalStateException {
Trans trans = (Trans) localTrans.get();
if (trans != null && trans.txn != null) {
Transaction parent = closeTxn(trans);
trans.txn.abort();
return parent;
} else {
throw new IllegalStateException("No transaction is active");
}
}
/**
* Returns whether the current transaction is a readUncommitted
* transaction.
*/
final boolean isReadUncommitted() {
Trans trans = (Trans) localTrans.get();
if (trans != null && trans.config != null) {
return trans.config.getReadUncommitted();
} else {
return false;
}
}
private Transaction closeTxn(Trans trans) {
localTrans.set(trans.parent);
return (trans.parent != null) ? trans.parent.txn : null;
}
private static class Trans {
private Trans parent;
private Transaction txn;
private TransactionConfig config;
private Trans(Trans parent, TransactionConfig config) {
this.parent = parent;
this.config = config;
}
}
/**
* Opens a cursor for a given database, dup'ing an existing CDB cursor if
* one is open for the current thread.
*/
Cursor openCursor(Database db,
CursorConfig cursorConfig,
boolean writeCursor,
Transaction txn)
throws DatabaseException {
if (cdbMode) {
CdbCursors cdbCursors = null;
WeakHashMap cdbCursorsMap = (WeakHashMap) localCdbCursors.get();
if (cdbCursorsMap == null) {
cdbCursorsMap = new WeakHashMap();
localCdbCursors.set(cdbCursorsMap);
} else {
cdbCursors = (CdbCursors) cdbCursorsMap.get(db);
}
if (cdbCursors == null) {
cdbCursors = new CdbCursors();
cdbCursorsMap.put(db, cdbCursors);
}
/*
* In CDB mode the cursorConfig specified by the user is ignored
* and only the writeCursor parameter is honored. This is the only
* meaningful cursor attribute for CDB, and here we count on
* writeCursor flag being set correctly by the caller.
*/
List cursors;
CursorConfig cdbConfig;
if (writeCursor) {
if (cdbCursors.readCursors.size() > 0) {
/*
* Although CDB allows opening a write cursor when a read
* cursor is open, a self-deadlock will occur if a write is
* attempted for a record that is read-locked; we should
* avoid self-deadlocks at all costs
*/
throw new IllegalStateException
("Cannot open CDB write cursor when read cursor " +
"is open");
}
cursors = cdbCursors.writeCursors;
cdbConfig = new CursorConfig();
DbCompat.setWriteCursor(cdbConfig, true);
} else {
cursors = cdbCursors.readCursors;
cdbConfig = null;
}
Cursor cursor;
if (cursors.size() > 0) {
Cursor other = ((Cursor) cursors.get(0));
cursor = other.dup(false);
} else {
cursor = db.openCursor(null, cdbConfig);
}
cursors.add(cursor);
return cursor;
} else {
return db.openCursor(txn, cursorConfig);
}
}
/**
* Duplicates a cursor for a given database.
*
* @param writeCursor true to open a write cursor in a CDB environment, and
* ignored for other environments.
*
* @param samePosition is passed through to Cursor.dup().
*
* @return the open cursor.
*
* @throws DatabaseException if a database problem occurs.
*/
Cursor dupCursor(Cursor cursor, boolean writeCursor, boolean samePosition)
throws DatabaseException {
if (cdbMode) {
WeakHashMap cdbCursorsMap = (WeakHashMap) localCdbCursors.get();
if (cdbCursorsMap != null) {
Database db = cursor.getDatabase();
CdbCursors cdbCursors = (CdbCursors) cdbCursorsMap.get(db);
if (cdbCursors != null) {
List cursors = writeCursor ? cdbCursors.writeCursors
: cdbCursors.readCursors;
if (cursors.contains(cursor)) {
Cursor newCursor = cursor.dup(samePosition);
cursors.add(newCursor);
return newCursor;
}
}
}
throw new IllegalStateException("Cursor to dup not tracked");
} else {
return cursor.dup(samePosition);
}
}
/**
* Closes a cursor.
*
* @param cursor the cursor to close.
*
* @throws DatabaseException if a database problem occurs.
*/
void closeCursor(Cursor cursor)
throws DatabaseException {
if (cursor == null) {
return;
}
if (cdbMode) {
WeakHashMap cdbCursorsMap = (WeakHashMap) localCdbCursors.get();
if (cdbCursorsMap != null) {
Database db = cursor.getDatabase();
CdbCursors cdbCursors = (CdbCursors) cdbCursorsMap.get(db);
if (cdbCursors != null) {
if (cdbCursors.readCursors.remove(cursor) ||
cdbCursors.writeCursors.remove(cursor)) {
cursor.close();
return;
}
}
}
throw new IllegalStateException
("Closing CDB cursor that was not known to be open");
} else {
cursor.close();
}
}
/**
* Returns true if a CDB cursor is open and therefore a Database write
* operation should not be attempted since a self-deadlock may result.
*/
boolean isCDBCursorOpen(Database db) {
if (cdbMode) {
WeakHashMap cdbCursorsMap = (WeakHashMap) localCdbCursors.get();
if (cdbCursorsMap != null) {
CdbCursors cdbCursors = (CdbCursors) cdbCursorsMap.get(db);
if (cdbCursors != null &&
(cdbCursors.readCursors.size() > 0 ||
cdbCursors.writeCursors.size() > 0)) {
return true;
}
}
}
return false;
}
static final class CdbCursors {
List writeCursors = new ArrayList();
List readCursors = new ArrayList();
}
}