[libpostgresql-jdbc-java] 04/12: Fix a deadlock that occurs when retrieving notifications. Normal query execution enters the QueryExecutor monitor and then calls a synchronized method in the ProtocolConnection to update the transaction state. Notification retrieval operates in the reverse order, entering the ProtocolConnection monitor and then calling a synchronized method in the QueryExecutor.

[Emmanuel Bourg]

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ebourg-guest pushed a commit to tag REL8_3_604
in repository libpostgresql-jdbc-java.

commit dc8fe8fe53e0e6943463512c40d6120e4d701013
Author: Kris Jurka <books at ejurka.com>
Date:   Tue Apr 1 07:19:29 2008 +0000

    Fix a deadlock that occurs when retrieving notifications.  Normal
    query execution enters the QueryExecutor monitor and then calls a
    synchronized method in the ProtocolConnection to update the
    transaction state.  Notification retrieval operates in the reverse
    order, entering the ProtocolConnection monitor and then calling a
    synchronized method in the QueryExecutor.
    
    Remove the QueryExecutor call from ProtocolConnection and make the
    higher level code responsible for calling it so we always acquire
    locks in the same order.
    
    Report and diagnosis by Joao Rui Leal.
---
 org/postgresql/core/QueryExecutor.java             | 11 ++++++++++-
 org/postgresql/core/v2/ProtocolConnectionImpl.java |  3 +--
 org/postgresql/core/v3/ProtocolConnectionImpl.java |  3 +--
 org/postgresql/jdbc2/AbstractJdbc2Connection.java  |  3 ++-
 4 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/org/postgresql/core/QueryExecutor.java b/org/postgresql/core/QueryExecutor.java
index b0aea2c..05c5f1b 100644
--- a/org/postgresql/core/QueryExecutor.java
+++ b/org/postgresql/core/QueryExecutor.java
@@ -4,7 +4,7 @@
 * Copyright (c) 2004, Open Cloud Limited.
 *
 * IDENTIFICATION
-*   $PostgreSQL: pgjdbc/org/postgresql/core/QueryExecutor.java,v 1.40 2005/02/01 07:27:53 jurka Exp $
+*   $PostgreSQL: pgjdbc/org/postgresql/core/QueryExecutor.java,v 1.41 2008/01/08 06:56:27 jurka Exp $
 *
 *-------------------------------------------------------------------------
 */
@@ -170,6 +170,15 @@ public interface QueryExecutor {
      */
     Query createParameterizedQuery(String sql); // Parsed for parameter placeholders ('?')
 
+    /**
+     * Prior to attempting to retrieve notifications, we need to pull
+     * any recently received notifications off of the network buffers.
+     * The notification retrieval in ProtocolConnection cannot do this
+     * as it is prone to deadlock, so the higher level caller must be
+     * responsible which requires exposing this method.
+     */
+    void processNotifies() throws SQLException;
+
     //
     // Fastpath interface.
     //
diff --git a/org/postgresql/core/v2/ProtocolConnectionImpl.java b/org/postgresql/core/v2/ProtocolConnectionImpl.java
index 2502401..1776659 100644
--- a/org/postgresql/core/v2/ProtocolConnectionImpl.java
+++ b/org/postgresql/core/v2/ProtocolConnectionImpl.java
@@ -4,7 +4,7 @@
 * Copyright (c) 2004, Open Cloud Limited.
 *
 * IDENTIFICATION
-*   $PostgreSQL: pgjdbc/org/postgresql/core/v2/ProtocolConnectionImpl.java,v 1.10 2006/12/01 08:53:45 jurka Exp $
+*   $PostgreSQL: pgjdbc/org/postgresql/core/v2/ProtocolConnectionImpl.java,v 1.11 2008/01/08 06:56:27 jurka Exp $
 *
 *-------------------------------------------------------------------------
 */
@@ -62,7 +62,6 @@ class ProtocolConnectionImpl implements ProtocolConnection {
     }
 
     public synchronized PGNotification[] getNotifications() throws SQLException {
-        executor.processNotifies();
         PGNotification[] array = (PGNotification[])notifications.toArray(new PGNotification[notifications.size()]);
         notifications.clear();
         return array;
diff --git a/org/postgresql/core/v3/ProtocolConnectionImpl.java b/org/postgresql/core/v3/ProtocolConnectionImpl.java
index 35e6852..4fbef08 100644
--- a/org/postgresql/core/v3/ProtocolConnectionImpl.java
+++ b/org/postgresql/core/v3/ProtocolConnectionImpl.java
@@ -4,7 +4,7 @@
 * Copyright (c) 2004, Open Cloud Limited.
 *
 * IDENTIFICATION
-*   $PostgreSQL: pgjdbc/org/postgresql/core/v3/ProtocolConnectionImpl.java,v 1.11 2006/12/01 08:53:45 jurka Exp $
+*   $PostgreSQL: pgjdbc/org/postgresql/core/v3/ProtocolConnectionImpl.java,v 1.12 2008/01/08 06:56:27 jurka Exp $
 *
 *-------------------------------------------------------------------------
 */
@@ -65,7 +65,6 @@ class ProtocolConnectionImpl implements ProtocolConnection {
     }
 
     public synchronized PGNotification[] getNotifications() throws SQLException {
-        executor.processNotifies();
         PGNotification[] array = (PGNotification[])notifications.toArray(new PGNotification[notifications.size()]);
         notifications.clear();
         return array;
diff --git a/org/postgresql/jdbc2/AbstractJdbc2Connection.java b/org/postgresql/jdbc2/AbstractJdbc2Connection.java
index 1005de6..6b97666 100644
--- a/org/postgresql/jdbc2/AbstractJdbc2Connection.java
+++ b/org/postgresql/jdbc2/AbstractJdbc2Connection.java
@@ -3,7 +3,7 @@
 * Copyright (c) 2004-2008, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
-*   $PostgreSQL: pgjdbc/org/postgresql/jdbc2/AbstractJdbc2Connection.java,v 1.47 2008/01/08 06:56:28 jurka Exp $
+*   $PostgreSQL: pgjdbc/org/postgresql/jdbc2/AbstractJdbc2Connection.java,v 1.47.2.1 2008/02/19 06:12:33 jurka Exp $
 *
 *-------------------------------------------------------------------------
 */
@@ -1022,6 +1022,7 @@ public abstract class AbstractJdbc2Connection implements BaseConnection
 
     public PGNotification[] getNotifications() throws SQLException
     {
+        getQueryExecutor().processNotifies();
         // Backwards-compatibility hand-holding.
         PGNotification[] notifications = protoConnection.getNotifications();
         return (notifications.length == 0 ? null : notifications);

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