We need to ensure that only one repository operation is active on a particular

JDBC connection at a time. JDBC connections are thread safe, but we frequently
have to execute statements like:

insert into FOO values(0, blah, blah);
select LAST_INSERTED_ID()

to get the value assigned to an auto-increment column. If another thread
slipped in between those statements and inserted something into its own
auto-increment column having table, we'd get funny business. And indeed we very
occasionally see this race condition happen in the thread-happy webapps.


git-svn-id: https://samskivert.googlecode.com/svn/trunk@1838 6335cc39-0255-0410-8fd6-9bcaacd3b74c

src/java/com/samskivert/jdbc/SimpleRepository.java

@@ -142,9 +142,13 @@ public class SimpleRepository extends Repository
             Thread.dumpStack();
         }
 
-        try {
         // obtain our database connection and associated goodies
         conn = _provider.getConnection(_dbident, readOnly);
+
+        // make sure that no one else performs a database operation using the
+        // same connection until we're done
+        synchronized (conn) {
+            try {
                 liaison = LiaisonRegistry.getLiaison(conn);
 
                 // find out if we support transactions
@@ -181,34 +185,30 @@ public class SimpleRepository extends Repository
                         }
                     } catch (SQLException rbe) {
                         Log.warning("Unable to roll back operation " +
-                                "[origerr=" + sqe + ", rberr=" + rbe + "].");
+                                    "[err=" + sqe + ", rberr=" + rbe + "].");
                     }
                 }
 
                 if (conn != null) {
-                // let the connection provider know that the connection failed
+                    // let the provider know that the connection failed
                     _provider.connectionFailed(_dbident, readOnly, conn, sqe);
-
                     // clear out the reference so that we don't release it later
                     conn = null;
                 }
 
-            // if this is a transient failure and we've been requested to
+                if (!retryOnTransientFailure || liaison == null ||
-            // retry such failures, try one more time
+                    !liaison.isTransientException(sqe)) {
-            if (retryOnTransientFailure &&
+                    String err = "Operation invocation failed";
-                liaison != null && liaison.isTransientException(sqe)) {
+                    throw new PersistenceException(err, sqe);
-                // the MySQL JDBC driver has the annoying habit of
+                }
-                // including the embedded exception stack trace in the
+
-                // message of their outer exception; if I want a fucking
+                // the MySQL JDBC driver has the annoying habit of including
-                // stack trace, I'll call printStackTrace() thanksverymuch
+                // the embedded exception stack trace in the message of their
+                // outer exception; if I want a fucking stack trace, I'll call
+                // printStackTrace() thanksverymuch
                 String msg = StringUtil.split("" + sqe, "\n")[0];
                 Log.info("Transient failure executing operation, " +
                          "retrying [error=" + msg + "].");
-                return execute(op, false, readOnly);
-            }
-
-            String err = "Operation invocation failed";
-            throw new PersistenceException(err, sqe);
 
             } catch (PersistenceException pe) {
                 // back out our changes if something got hosed
@@ -225,7 +225,8 @@ public class SimpleRepository extends Repository
             } catch (RuntimeException rte) {
                 // back out our changes if something got hosed
                 try {
-                if (conn != null && supportsTransactions && !conn.isClosed()) {
+                    if (supportsTransactions &&
+                        conn != null && !conn.isClosed()) {
                         conn.rollback();
                     }
                 } catch (SQLException rbe) {
@@ -242,6 +243,12 @@ public class SimpleRepository extends Repository
             }
         }
 
+        // we'll only fall through here if the above code failed due to a
+        // transient exception (the connection was closed for being idle, for
+        // example) and we've been asked to retry; so let's do so
+        return execute(op, false, readOnly);
+    }
+
     /**
      * Executes the supplied update query in this repository, returning
      * the number of rows modified.