Atomic change of transaction state

h2/src/main/org/h2/mvstore/tx/Transaction.java

@@ -10,6 +10,7 @@ import org.h2.mvstore.MVMap;
 import org.h2.mvstore.MVStore;
 import org.h2.mvstore.type.DataType;
 import java.util.Iterator;
+import java.util.concurrent.atomic.AtomicLong;
 
 /**
  * A transaction.
@@ -39,6 +40,35 @@ public class Transaction {
      */
     public static final int STATUS_COMMITTING = 3;
 
+    /**
+     * The status of a transaction that has been logically committed or rather
+     * marked as committed, because it might be still listed among prepared,
+     * if it was prepared for commit, undo log entries might still exists for it
+     * and not all of it's changes within map's are re-written as committed yet.
+     * Nevertheless, those changes should be already viewed by other
+     * transactions as committed.
+     * This transaction's id can not be re-used until all the above is completed
+     * and transaction is closed.
+     */
+    public static final int STATUS_COMMITTED    = 4;
+
+    /**
+     * The status of a transaction that currently in a process of rolling back
+     * to a savepoint.
+     */
+    private static final int STATUS_ROLLING_BACK = 5;
+
+    /**
+     * The status of a transaction that has been rolled back completely,
+     * but undo operations are not finished yet.
+     */
+    private static final int STATUS_ROLLED_BACK  = 6;
+
+    private static final String STATUS_NAMES[] = {
+            "CLOSED", "OPEN", "PREPARED", "COMMITTING",
+            "COMMITTED", "ROLLING_BACK", "ROLLED_BACK"
+    };
+
     /**
      * The transaction store.
      */
@@ -49,12 +79,13 @@ public class Transaction {
      */
     final int transactionId;
 
-    /**
-     * The log id of the last entry in the undo log map.
+    /*
+     * Transation state is an atomic composite field:
+     * bit 44       : flag whether transaction had rollback(s)
+     * bits 42-40   : status
+     * bits 39-0    : log id of the last entry in the undo log map
      */
-    long logId;
-
-    private int status;
+    private final AtomicLong statusAndLogId;
 
     private MVStore.TxCounter txCounter;
 
@@ -64,9 +95,8 @@ public class Transaction {
                 String name, long logId) {
         this.store = store;
         this.transactionId = transactionId;
-        this.status = status;
+        this.statusAndLogId = new AtomicLong(composeState(status, logId, false));
         this.name = name;
-        this.logId = logId;
     }
 
     public int getId() {
@@ -74,11 +104,60 @@ public class Transaction {
     }
 
     public int getStatus() {
-        return status;
+        return getStatus(statusAndLogId.get());
     }
 
-    void setStatus(int status) {
-        this.status = status;
+    long setStatus(int status) {
+        while (true) {
+            long currentState = statusAndLogId.get();
+            long logId = getLogId(currentState);
+            int currentStatus = getStatus(currentState);
+            boolean valid;
+            switch (status) {
+                case STATUS_OPEN:
+                    valid = currentStatus == STATUS_CLOSED ||
+                            currentStatus == STATUS_ROLLING_BACK;
+                    break;
+                case STATUS_ROLLING_BACK:
+                    valid = currentStatus == STATUS_OPEN;
+                    break;
+                case STATUS_PREPARED:
+                    valid = currentStatus == STATUS_OPEN;
+                    break;
+                case STATUS_COMMITTING:
+                    valid = currentStatus == STATUS_OPEN ||
+                            currentStatus == STATUS_PREPARED ||
+                            // this case is only possible if called
+                            // from endLeftoverTransactions()
+                            currentStatus == STATUS_COMMITTING;
+                    break;
+                case STATUS_COMMITTED:
+                    valid = currentStatus == STATUS_COMMITTING;
+                    break;
+                case STATUS_ROLLED_BACK:
+                    valid = currentStatus == STATUS_OPEN ||
+                            currentStatus == STATUS_PREPARED;
+                    break;
+                case STATUS_CLOSED:
+                    valid = currentStatus == STATUS_COMMITTING ||
+                            currentStatus == STATUS_COMMITTED ||
+                            currentStatus == STATUS_ROLLED_BACK;
+                    break;
+               default:
+                   valid = false;
+                   break;
+            }
+            if (!valid) {
+                throw DataUtils.newIllegalStateException(
+                        DataUtils.ERROR_TRANSACTION_ILLEGAL_STATE,
+                        "Transaction was illegally transitioned from {0} to {1}",
+                        STATUS_NAMES[currentStatus], STATUS_NAMES[status]);
+            }
+            long newState = composeState(status, logId, hasRollback(currentState));
+            if (statusAndLogId.compareAndSet(currentState, newState)) {
+                return currentState;
+            }
+        }
     }
 
     public void setName(String name) {
@@ -97,7 +176,7 @@ public class Transaction {
      * @return the savepoint id
      */
     public long setSavepoint() {
-        return logId;
+        return getLogId();
     }
 
     public void markStatementStart() {
@@ -120,17 +199,19 @@ public class Transaction {
      * @param key the key
      * @param oldValue the old value
      */
-    void log(int mapId, Object key, Object oldValue) {
+    void log(int mapId, Object key, VersionedValue oldValue) {
+        long currentState = statusAndLogId.getAndIncrement();
+        long logId = getLogId(currentState);
         store.log(this, logId, mapId, key, oldValue);
-        // only increment the log id if logging was successful
-        logId++;
     }
 
     /**
      * Remove the last log entry.
      */
     void logUndo() {
-        store.logUndo(this, --logId);
+        long currentState = statusAndLogId.decrementAndGet();
+        long logId = getLogId(currentState);
+        store.logUndo(this, logId);
     }
 
     /**
@@ -157,11 +238,8 @@ public class Transaction {
      */
     public <K, V> TransactionMap<K, V> openMap(String name,
                                                DataType keyType, DataType valueType) {
-        checkNotClosed();
-        MVMap<K, VersionedValue> map = store.openMap(name, keyType,
-                valueType);
-        int mapId = map.getId();
-        return new TransactionMap<>(this, map, mapId);
+        MVMap<K, VersionedValue> map = store.openMap(name, keyType, valueType);
+        return openMap(map);
     }
 
     /**
@@ -172,8 +250,7 @@ public class Transaction {
      * @param map the base map
      * @return the transactional map
      */
-    public <K, V> TransactionMap<K, V> openMap(
-            MVMap<K, VersionedValue> map) {
+    public <K, V> TransactionMap<K, V> openMap(MVMap<K, VersionedValue> map) {
         checkNotClosed();
         int mapId = map.getId();
         return new TransactionMap<>(this, map, mapId);
@@ -181,11 +258,10 @@ public class Transaction {
 
     /**
      * Prepare the transaction. Afterwards, the transaction can only be
-     * committed or rolled back.
+     * committed or completely rolled back.
      */
     public void prepare() {
-        checkNotClosed();
-        status = STATUS_PREPARED;
+        setStatus(STATUS_PREPARED);
         store.storeTransaction(this);
     }
 
@@ -193,8 +269,10 @@ public class Transaction {
      * Commit the transaction. Afterwards, this transaction is closed.
      */
     public void commit() {
-        checkNotClosed();
-        store.commit(this, logId);
+        long state = setStatus(Transaction.STATUS_COMMITTING);
+        long logId = Transaction.getLogId(state);
+        int oldStatus = Transaction.getStatus(state);
+        store.commit(this, logId, oldStatus);
     }
 
     /**
@@ -204,18 +282,36 @@ public class Transaction {
      * @param savepointId the savepoint id
      */
     public void rollbackToSavepoint(long savepointId) {
-        checkNotClosed();
+        long lastState = setStatus(STATUS_ROLLING_BACK);
+        long logId = getLogId(lastState);
+        try {
             store.rollbackTo(this, logId, savepointId);
-        logId = savepointId;
+        } finally {
+            long expectedState = composeState(STATUS_ROLLING_BACK, logId, hasRollback(lastState));
+            long newState = composeState(STATUS_OPEN, savepointId, true);
+            if (!statusAndLogId.compareAndSet(expectedState, newState)) {
+                throw DataUtils.newIllegalStateException(
+                        DataUtils.ERROR_TRANSACTION_ILLEGAL_STATE,
+                        "Transaction {0} concurrently modified " +
+                                "while rollback to savepoint was in progress",
+                        transactionId);
+            }
+        }
     }
 
     /**
      * Roll the transaction back. Afterwards, this transaction is closed.
      */
     public void rollback() {
-        checkNotClosed();
+        try {
+            long lastState = setStatus(STATUS_ROLLED_BACK);
+            long logId = getLogId(lastState);
+            if (logId > 0) {
                 store.rollbackTo(this, logId, 0);
-        store.endTransaction(this, status);
+            }
+        } finally {
+            store.endTransaction(this, STATUS_ROLLED_BACK);
+        }
     }
 
     /**
@@ -228,14 +324,18 @@ public class Transaction {
      * @return the changes
      */
     public Iterator<TransactionStore.Change> getChanges(long savepointId) {
-        return store.getChanges(this, logId, savepointId);
+        return store.getChanges(this, getLogId(), savepointId);
+    }
+
+    long getLogId() {
+        return getLogId(statusAndLogId.get());
     }
 
     /**
      * Check whether this transaction is open or prepared.
      */
     void checkNotClosed() {
-        if (status == STATUS_CLOSED) {
+        if (getStatus() == STATUS_CLOSED) {
             throw DataUtils.newIllegalStateException(
                     DataUtils.ERROR_CLOSED, "Transaction is closed");
         }
@@ -252,7 +352,31 @@ public class Transaction {
 
     @Override
     public String toString() {
-        return "" + transactionId;
+        long state = statusAndLogId.get();
+        return transactionId + " " +  STATUS_NAMES[getStatus(state)] + " " + getLogId(state);
     }
 
+
+    public static int getStatus(long state) {
+        return (int)(state >>> 40) & 15;
+    }
+
+    public static long getLogId(long state) {
+        return state & ((1L << 40) - 1);
+    }
+
+    private static boolean hasRollback(long state) {
+        return (state & (1L << 44)) != 0;
+    }
+
+    private static boolean hasChanges(long state) {
+        return getLogId(state) != 0;
+    }
+
+    private static long composeState(int status, long logId, boolean hasRollback) {
+        if (hasRollback) {
+            status |= 16;
+        }
+        return ((long)status << 40) | logId;
+    }
 }

h2/src/main/org/h2/mvstore/tx/TransactionMap.java

@@ -277,7 +277,7 @@ public class TransactionMap<K, V> {
             }
         }
         VersionedValue newValue = new VersionedValue(
-                TransactionStore.getOperationId(transaction.transactionId, transaction.logId),
+                TransactionStore.getOperationId(transaction.transactionId, transaction.getLogId()),
                 value);
         if (current == null) {
             // a new value

h2/src/main/org/h2/mvstore/tx/TransactionStore.java

@@ -345,16 +345,15 @@ public class TransactionStore {
      *
      * @param t the transaction
      * @param maxLogId the last log id
+     * @param oldStatus last status
      */
-    void commit(Transaction t, long maxLogId) {
+    void commit(Transaction t, long maxLogId, int oldStatus) {
         if (store.isClosed()) {
             return;
         }
         // TODO could synchronize on blocks (100 at a time or so)
         rwLock.writeLock().lock();
-        int oldStatus = t.getStatus();
         try {
-            t.setStatus(Transaction.STATUS_COMMITTING);
             for (long logId = 0; logId < maxLogId; logId++) {
                 Long undoKey = getOperationId(t.getId(), logId);
                 Object[] op = undoLog.get(undoKey);