add some debugging for meta locking

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

@@ -899,6 +899,9 @@ public class Database implements DataHandler {
         }
     }
 
+    private static final ThreadLocal<Session> metaLockDebugging = new ThreadLocal<Session>();
+    private static final ThreadLocal<Throwable> metaLockDebuggingStack = new ThreadLocal<Throwable>();
+
     /**
      * Lock the metadata table for updates.
      *
@@ -913,6 +916,19 @@ public class Database implements DataHandler {
         if (meta == null) {
             return true;
         }
+        if (SysProperties.CHECK2) {
+            final Session prev = metaLockDebugging.get();
+            if (prev == null) {
+                metaLockDebugging.set(session);
+                metaLockDebuggingStack.set(new Throwable());
+            } else if (prev != session) {
+                metaLockDebuggingStack.get().printStackTrace();
+                throw new IllegalStateException("meta currently locked by "
+                        + prev
+                        + " and trying to be locked by different session, "
+                        + session + " on same thread");
+            }
+        }
         boolean wasLocked = meta.lock(session, true, true);
         return wasLocked;
     }
@@ -923,10 +939,20 @@ public class Database implements DataHandler {
      * @param session the session
      */
     public void unlockMeta(Session session) {
+        unlockMetaDebug(session);
         meta.unlock(session);
         session.unlock(meta);
     }
 
+    public void unlockMetaDebug(Session session) {
+        if (SysProperties.CHECK2) {
+            if (metaLockDebugging.get() == session) {
+                metaLockDebugging.set(null);
+                metaLockDebuggingStack.set(null);
+            }
+        }
+    }
+
     /**
      * Remove the given object from the meta data.
      *
@@ -956,6 +982,7 @@ public class Database implements DataHandler {
                     checkMetaFree(session, id);
                 }
             } else if (!wasLocked) {
+                unlockMetaDebug(session);
                 // must not keep the lock if it was not locked
                 // otherwise updating sequences may cause a deadlock
                 meta.unlock(session);

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

@@ -856,6 +856,9 @@ public class Session extends SessionWithState {
 
                 removeTemporaryLobs(false);
                 cleanTempTables(true);
+                // sometimes Table#removeChildrenAndResources
+                // will take the meta lock
+                database.unlockMeta(this);
                 undoLog.clear();
                 database.removeSession(this);
             } finally {
@@ -965,6 +968,7 @@ public class Session extends SessionWithState {
             }
             locks.clear();
         }
+        database.unlockMetaDebug(this);
         savepoints = null;
         sessionStateChanged = true;
     }
@@ -991,11 +995,6 @@ public class Session extends SessionWithState {
                         table.truncate(this);
                     }
                 }
-                // sometimes Table#removeChildrenAndResources
-                // will take the meta lock
-                if (closeSession) {
-                    database.unlockMeta(this);
-                }
             }
         }
     }