Use exact maths in the CommunityLockManager

community/kernel/src/main/java/org/neo4j/helpers/MathUtil.java

@@ -89,5 +89,18 @@ public static int compareLongAgainstDouble( long lhs, double rhs )
     {
         return - compareDoubleAgainstLong( rhs, lhs );
     }
+
+    /**
+     * Return an integer one less than the given integer, or throw {@link ArithmeticException} if the given integer is
+     * zero.
+     */
+    public static int decrementExactNotPastZero( int value )
+    {
+        if ( value == 0 )
+        {
+            throw new ArithmeticException( "integer underflow past zero" );
+        }
+        return value - 1;
+    }
 }
 

community/kernel/src/main/java/org/neo4j/kernel/impl/locking/LockClientStateHolder.java

@@ -81,7 +81,7 @@ public boolean incrementActiveClients()
                 return false;
             }
         }
-        while ( !clientState.compareAndSet( currentState, statusWithUpdatedClients( currentState, 1 ) ) );
+        while ( !clientState.compareAndSet( currentState, incrementActiveClients( currentState ) ) );
         return true;
     }
 
@@ -95,7 +95,7 @@ public void decrementActiveClients()
         {
             currentState = clientState.get();
         }
-        while ( !clientState.compareAndSet( currentState, statusWithUpdatedClients( currentState, -1 ) ) );
+        while ( !clientState.compareAndSet( currentState, decrementActiveClients( currentState ) ) );
     }
 
     /**
@@ -136,8 +136,13 @@ private int stateWithNewStatus( int clientState, int newStatus )
         return newStatus | getActiveClients( clientState );
     }
 
-    private int statusWithUpdatedClients( int clientState, int delta )
+    private int incrementActiveClients( int clientState )
     {
-        return getStatus( clientState ) | Math.addExact( getActiveClients( clientState ), delta );
+        return getStatus( clientState ) | Math.incrementExact( getActiveClients( clientState ) );
+    }
+
+    private int decrementActiveClients( int clientState )
+    {
+        return getStatus( clientState ) | Math.decrementExact( getActiveClients( clientState ) );
     }
 }

community/kernel/src/main/java/org/neo4j/kernel/impl/locking/community/LockResource.java

@@ -19,6 +19,7 @@
  */
 package org.neo4j.kernel.impl.locking.community;
 
+import org.neo4j.helpers.MathUtil;
 import org.neo4j.storageengine.api.lock.ResourceType;
 
 public class LockResource
@@ -77,12 +78,12 @@ public String toString()
 
     public void acquireReference()
     {
-        refCount++;
+        refCount = Math.incrementExact( refCount );
     }
 
     public int releaseReference()
     {
-        return --refCount;
+        return refCount = MathUtil.decrementExactNotPastZero( refCount );
     }
 
     public long resourceId()

community/kernel/src/main/java/org/neo4j/kernel/impl/locking/community/RWLock.java

@@ -23,6 +23,7 @@
 import java.util.LinkedList;
 import java.util.ListIterator;
 
+import org.neo4j.helpers.MathUtil;
 import org.neo4j.kernel.DeadlockDetectedException;
 import org.neo4j.kernel.impl.locking.LockType;
 import org.neo4j.kernel.impl.util.ArrayMap;
@@ -99,12 +100,12 @@ private static class TxLockElement
 
         void incrementRequests()
         {
-            requests++;
+            requests = Math.incrementExact( requests );
         }
 
         void decrementRequests()
         {
-            requests--;
+            requests = MathUtil.decrementExactNotPastZero( requests );
         }
 
         boolean hasNoRequests()
@@ -151,7 +152,13 @@ public Object resource()
 
     synchronized void mark()
     {
-        this.marked++;
+        marked = Math.incrementExact( marked );
+    }
+
+    /** synchronized by all caller methods */
+    private void unmark()
+    {
+        marked = MathUtil.decrementExactNotPastZero( marked );
     }
 
     synchronized boolean isMarked()
@@ -233,7 +240,7 @@ synchronized boolean acquireReadLock( Object tx ) throws DeadlockDetectedExcepti
             interrupted();
             // if deadlocked, remove marking so lock is removed when empty
             tle.decrementRequests();
-            marked--;
+            unmark();
         }
     }
 
@@ -254,7 +261,7 @@ synchronized boolean tryAcquireReadLock( Object tx )
         finally
         {
             // if deadlocked, remove marking so lock is removed when empty
-            marked--;
+            unmark();
         }
     }
 
@@ -276,8 +283,8 @@ synchronized void releaseReadLock( Object tx ) throws LockNotFoundException
             throw new LockNotFoundException( "" + tx + " don't have readLock" );
         }
 
-        totalReadCount--;
-        tle.readCount--;
+        totalReadCount = MathUtil.decrementExactNotPastZero( totalReadCount );
+        tle.readCount = MathUtil.decrementExactNotPastZero( tle.readCount );
         if ( tle.isFree() )
         {
             ragManager.lockReleased( this, tx );
@@ -419,7 +426,7 @@ synchronized boolean acquireWriteLock( Object tx ) throws DeadlockDetectedExcept
             interrupted();
             // if deadlocked, remove marking so lock is removed when empty
             tle.decrementRequests();
-            marked--;
+            unmark();
         }
     }
 
@@ -451,7 +458,7 @@ synchronized boolean tryAcquireWriteLock( Object tx )
         finally
         {
             // if deadlocked, remove marking so lock is removed when empty
-            marked--;
+            unmark();
         }
     }
 
@@ -473,8 +480,8 @@ synchronized void releaseWriteLock( Object tx ) throws LockNotFoundException
             throw new LockNotFoundException( "" + tx + " don't have writeLock" );
         }
 
-        totalWriteCount--;
-        tle.writeCount--;
+        totalWriteCount = MathUtil.decrementExactNotPastZero( totalWriteCount );
+        tle.writeCount = MathUtil.decrementExactNotPastZero( tle.writeCount );
         if ( tle.isFree() )
         {
             ragManager.lockReleased( this, tx );
@@ -587,7 +594,7 @@ public synchronized String describe()
 
     public synchronized long maxWaitTime()
     {
-        long max = 0l;
+        long max = 0L;
         for ( LockRequest thread : waitingThreadList )
         {
             if ( thread.since < max )
@@ -624,15 +631,15 @@ public String toString()
     private void registerReadLockAcquired( Object tx, TxLockElement tle )
     {
         registerLockAcquired( tx, tle );
-        totalReadCount++;
-        tle.readCount++;
+        totalReadCount = Math.incrementExact( totalReadCount );
+        tle.readCount = Math.incrementExact( tle.readCount );
     }
 
     private void registerWriteLockAcquired( Object tx, TxLockElement tle )
     {
         registerLockAcquired( tx, tle );
-        totalWriteCount++;
-        tle.writeCount++;
+        totalWriteCount = Math.incrementExact( totalWriteCount );
+        tle.writeCount = Math.incrementExact( tle.writeCount );
     }
 
     private void registerLockAcquired( Object tx, TxLockElement tle )