since we have removed the synchronization from Database#lockMeta,

it now makes more sense to return a boolean for isLockedExclusivelyBy() from the lock()
method, to make it easier to reason about the atomic-ness of the operation

h2/src/main/org/h2/engine/Database.java

@@ -884,8 +884,7 @@ public class Database implements DataHandler {
         if (meta == null) {
             return true;
         }
-        boolean wasLocked = meta.isLockedExclusivelyBy(session);
-        meta.lock(session, true, true);
+        boolean wasLocked = meta.lock(session, true, true);
         return wasLocked;
     }
 

h2/src/main/org/h2/mvstore/db/MVTable.java

@@ -94,11 +94,11 @@ public class MVTable extends TableBase {
     }
 
     @Override
-    public void lock(Session session, boolean exclusive,
+    public boolean lock(Session session, boolean exclusive,
             boolean forceLockEvenInMvcc) {
         int lockMode = database.getLockMode();
         if (lockMode == Constants.LOCK_MODE_OFF) {
-            return;
+            return false;
         }
         if (!forceLockEvenInMvcc && database.isMultiVersion()) {
             // MVCC: update, delete, and insert use a shared lock.
@@ -109,12 +109,12 @@ public class MVTable extends TableBase {
                 exclusive = false;
             } else {
                 if (lockExclusiveSession == null) {
-                    return;
+                    return false;
                 }
             }
         }
         if (lockExclusiveSession == session) {
-            return;
+            return true;
         }
         synchronized (getLockSyncObject()) {
             session.setWaitForLock(this, Thread.currentThread());
@@ -126,6 +126,7 @@ public class MVTable extends TableBase {
                 waitingSessions.remove(session);
             }
         }
+        return false;
     }
 
     /**

h2/src/main/org/h2/table/FunctionTable.java

@@ -87,8 +87,9 @@ public class FunctionTable extends Table {
     }
 
     @Override
-    public void lock(Session session, boolean exclusive, boolean forceLockEvenInMvcc) {
+    public boolean lock(Session session, boolean exclusive, boolean forceLockEvenInMvcc) {
         // nothing to do
+        return false;
     }
 
     @Override

h2/src/main/org/h2/table/MetaTable.java

@@ -591,8 +591,9 @@ public class MetaTable extends Table {
     }
 
     @Override
-    public void lock(Session session, boolean exclusive, boolean forceLockEvenInMvcc) {
+    public boolean lock(Session session, boolean exclusive, boolean forceLockEvenInMvcc) {
         // nothing to do
+        return false;
     }
 
     @Override

h2/src/main/org/h2/table/RangeTable.java

@@ -64,8 +64,9 @@ public class RangeTable extends Table {
     }
 
     @Override
-    public void lock(Session session, boolean exclusive, boolean forceLockEvenInMvcc) {
+    public boolean lock(Session session, boolean exclusive, boolean forceLockEvenInMvcc) {
         // nothing to do
+        return false;
     }
 
     @Override

h2/src/main/org/h2/table/RegularTable.java

@@ -439,11 +439,11 @@ public class RegularTable extends TableBase {
     }
 
     @Override
-    public void lock(Session session, boolean exclusive,
+    public boolean lock(Session session, boolean exclusive,
             boolean forceLockEvenInMvcc) {
         int lockMode = database.getLockMode();
         if (lockMode == Constants.LOCK_MODE_OFF) {
-            return;
+            return lockExclusiveSession != null;
         }
         if (!forceLockEvenInMvcc && database.isMultiVersion()) {
             // MVCC: update, delete, and insert use a shared lock.
@@ -452,16 +452,16 @@ public class RegularTable extends TableBase {
                 exclusive = false;
             } else {
                 if (lockExclusiveSession == null) {
-                    return;
+                    return false;
                 }
             }
         }
         if (lockExclusiveSession == session) {
-            return;
+            return true;
         }
         synchronized (database) {
             if (lockExclusiveSession == session) {
-                return;
+                return true;
             }
             session.setWaitForLock(this, Thread.currentThread());
             waitingSessions.addLast(session);
@@ -472,6 +472,7 @@ public class RegularTable extends TableBase {
                 waitingSessions.remove(session);
             }
         }
+        return false;
     }
 
     private void doLock1(Session session, int lockMode, boolean exclusive) {

h2/src/main/org/h2/table/Table.java

@@ -134,9 +134,10 @@ public abstract class Table extends SchemaObjectBase {
      * @param session the session
      * @param exclusive true for write locks, false for read locks
      * @param forceLockEvenInMvcc lock even in the MVCC mode
+     * @return true if the table was already exclusively locked by this session.
      * @throws DbException if a lock timeout occurred
      */
-    public abstract void lock(Session session, boolean exclusive, boolean forceLockEvenInMvcc);
+    public abstract boolean lock(Session session, boolean exclusive, boolean forceLockEvenInMvcc);
 
     /**
      * Close the table object and flush changes.

h2/src/main/org/h2/table/TableLink.java

@@ -390,8 +390,9 @@ public class TableLink extends Table {
     }
 
     @Override
-    public void lock(Session session, boolean exclusive, boolean forceLockEvenInMvcc) {
+    public boolean lock(Session session, boolean exclusive, boolean forceLockEvenInMvcc) {
         // nothing to do
+        return false;
     }
 
     @Override

h2/src/main/org/h2/table/TableView.java

@@ -320,8 +320,9 @@ public class TableView extends Table {
     }
 
     @Override
-    public void lock(Session session, boolean exclusive, boolean forceLockEvenInMvcc) {
+    public boolean lock(Session session, boolean exclusive, boolean forceLockEvenInMvcc) {
         // exclusive lock means: the view will be dropped
+        return false;
     }
 
     @Override

h2/src/test/org/h2/test/db/TestTableEngines.java

@@ -341,8 +341,9 @@ public class TestTableEngines extends TestBase {
             }
 
             @Override
-            public void lock(Session session, boolean exclusive, boolean force) {
+            public boolean lock(Session session, boolean exclusive, boolean force) {
                 // do nothing
+                return false;
             }
 
             @Override