Provide a modicum of thread safety for marshaller init.

The _marshallers table must be guarded as computed marshallers can be created
at any time, and marshaller initialization itself must be guarded for the same
reason.

Thanks to Ray for pointing this out.

src/main/java/com/samskivert/depot/PersistenceContext.java

@@ -181,7 +181,7 @@ public class PersistenceContext
      * @param conprov provides JDBC {@link Connection} instances.
      * @param adapter an optional adapter to a cache management system.
      */
-    public void init (String ident, ConnectionProvider conprov, CacheAdapter adapter)
+    public synchronized void init (String ident, ConnectionProvider conprov, CacheAdapter adapter)
     {
         // if we have no URL for the ident, freak out now; lest confusing failure happen later
         String url = conprov.getURL(ident);
@@ -267,10 +267,8 @@ public class PersistenceContext
         Class<T> type, SchemaMigration migration)
     {
         DepotMarshaller<T> marshaller = getRawMarshaller(type);
-        if (marshaller.isInitialized()) {
-            throw new IllegalStateException(
-                "Migrations must be registered before initializeRepositories() is called.");
-        }
+        marshaller.requireInitialized(
+            "Migrations must be registered before initializeRepositories() is called.");
         marshaller.registerMigration(migration);
     }
 
@@ -284,10 +282,9 @@ public class PersistenceContext
         checkAreInitialized(); // le check du sanity
         DepotMarshaller<T> marshaller = getRawMarshaller(type);
         try {
-            if (!marshaller.isInitialized()) {
-                // initialize the marshaller which may create or migrate the table for its
-                // underlying persistent object
-                marshaller.init(this, _meta);
+            // initialize the marshaller which may create or migrate the table for its underlying
+            // persistent object
+            if (marshaller.init(this, _meta)) {
                 if (marshaller.getTableName() != null && _warnOnLazyInit) {
                     log.warning("Record initialized lazily", "type", type.getName(),
                                 new Exception());
@@ -568,10 +565,11 @@ public class PersistenceContext
     /**
      * Looks up and creates, but does not initialize, the marshaller for the specified Entity type.
      */
-    protected <T extends PersistentRecord> DepotMarshaller<T> getRawMarshaller (Class<T> type)
+    protected synchronized <T extends PersistentRecord> DepotMarshaller<T> getRawMarshaller (
+        Class<T> type)
     {
-        @SuppressWarnings("unchecked") DepotMarshaller<T> marshaller =
-            (DepotMarshaller<T>)_marshallers.get(type);
+        @SuppressWarnings("unchecked") DepotMarshaller<T> marshaller = (DepotMarshaller<T>)
+            _marshallers.get(type);
         if (marshaller == null) {
             _marshallers.put(type, marshaller = new DepotMarshaller<T>(type, this));
         }
@@ -664,7 +662,7 @@ public class PersistenceContext
         return invoke(op, false);
     }
 
-    protected void checkAreInitialized ()
+    protected synchronized void checkAreInitialized ()
     {
         if (_conprov == null) {
             throw new IllegalStateException(

src/main/java/com/samskivert/depot/impl/DepotMarshaller.java

@@ -456,27 +456,22 @@ public class DepotMarshaller<T extends PersistentRecord> implements QueryMarshal
     }
 
     /**
-     * Returns true if this marshaller has been initialized ({@link #init} has been called), its
-     * migrations run and it is ready for operation. False otherwise.
+     * Throws {@link IllegalStateException} with {@code msg} if this marshaller is not initialized.
      */
-    public boolean isInitialized ()
-    {
-        return _meta != null;
+    public synchronized void requireInitialized (String msg) {
+        if (_meta == null) throw new IllegalStateException(msg);
     }
 
     /**
-     * Initializes the table used by this marshaller. This is called automatically by the {@link
-     * PersistenceContext} the first time an entity is used. If the table does not exist, it will
-     * be created. If the schema version specified by the persistent object is newer than the
-     * database schema, it will be migrated.
+     * Initializes the table used by this marshaller if it has not yet been done. If the table does
+     * not exist, it will be created. If the schema version specified by the persistent object is
+     * newer than the database schema, it will be migrated.
+     * @return true if initialization was performed, false if it has already been performed.
      */
-    public void init (PersistenceContext ctx, DepotMetaData meta)
+    public synchronized boolean init (PersistenceContext ctx, DepotMetaData meta)
         throws DatabaseException
     {
-        if (_meta != null) { // sanity check
-            throw new IllegalStateException(
-                "Cannot re-initialize marshaller [type=" + _pClass + "].");
-        }
+        if (_meta != null) return false;
         _meta = meta;
 
         final SQLBuilder builder = ctx.getSQLBuilder(new DepotTypes(ctx, _pClass));
@@ -488,7 +483,7 @@ public class DepotMarshaller<T extends PersistentRecord> implements QueryMarshal
 
         // if we have no table (i.e. we're a computed entity), we have nothing to create
         if (getTableName() == null) {
-            return;
+            return true;
         }
 
         // figure out the list of fields that correspond to actual table columns and generate the
@@ -522,7 +517,7 @@ public class DepotMarshaller<T extends PersistentRecord> implements QueryMarshal
                 if (Boolean.getBoolean("com.samskivert.depot.verifyschema")) {
                     checkForStaleness(TableMetaData.load(ctx, getTableName()), ctx, builder);
                 }
-                return;
+                return true;
             }
 
             // check whether migrations are allowed by our context
@@ -530,7 +525,7 @@ public class DepotMarshaller<T extends PersistentRecord> implements QueryMarshal
             case WARN:
                 log.warning(_pClass.getName() + " requires migration, which is disallowed. " +
                             "Failures may be encountered later.");
-                return;
+                return true;
             case FAIL:
                 throw new DatabaseException(
                     _pClass.getName() + " requires migration, which is disallowed.");
@@ -577,6 +572,7 @@ public class DepotMarshaller<T extends PersistentRecord> implements QueryMarshal
             // and update our version in the schema version table
             _meta.updateVersion(getTableName(), _schemaVersion);
             expectedDbVersion = _schemaVersion;
+            return true;
 
         } finally {
             // set our migrating version back to zero