[activemq] branch main updated: AMQ-6660 - Use a separate lock for lazy scheduler creation to prevent deadlocks

[cshannon]

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cshannon pushed a commit to branch main
in repository https://gitbox.apache.org/repos/asf/activemq.git


The following commit(s) were added to refs/heads/main by this push:
     new 3f5abd4  AMQ-6660 - Use a separate lock for lazy scheduler creation to 
prevent deadlocks
3f5abd4 is described below

commit 3f5abd4433d3dca911ac418d899346e7dd675b7b
Author: Christopher L. Shannon (cshannon) <christopher.l.shan...@gmail.com>
AuthorDate: Fri Jun 25 10:54:36 2021 -0400

    AMQ-6660 - Use a separate lock for lazy scheduler creation to prevent
    deadlocks
    
    Switch to using a dedicated lock to initialize the Scheduler object
    inside of ActiveMQConnection to prevent a deadlock scenario that occurs
    when using the intrinsic ActiveMQConnection lock. This is using double
    checked locking so this lock will only be contended with during lazy
    creation and then will rely on the volatile reference for future reads
    and when stopping/closing.
---
 .../src/main/java/org/apache/activemq/ActiveMQConnection.java          | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git 
a/activemq-client/src/main/java/org/apache/activemq/ActiveMQConnection.java 
b/activemq-client/src/main/java/org/apache/activemq/ActiveMQConnection.java
index 6d8ce63..5d11fb6 100644
--- a/activemq-client/src/main/java/org/apache/activemq/ActiveMQConnection.java
+++ b/activemq-client/src/main/java/org/apache/activemq/ActiveMQConnection.java
@@ -200,6 +200,7 @@ public class ActiveMQConnection implements Connection, 
TopicConnection, QueueCon
     protected AtomicInteger transportInterruptionProcessingComplete = new 
AtomicInteger(0);
     private long consumerFailoverRedeliveryWaitPeriod;
     private volatile Scheduler scheduler;
+    private final Object schedulerLock = new Object();
     private boolean messagePrioritySupported = false;
     private boolean transactedIndividualAck = false;
     private boolean nonBlockingRedelivery = false;
@@ -2383,7 +2384,7 @@ public class ActiveMQConnection implements Connection, 
TopicConnection, QueueCon
                 // without lock contention report the closing state
                 throw new ConnectionClosedException();
             }
-            synchronized (this) {
+            synchronized (schedulerLock) {
                 result = scheduler;
                 if (result == null) {
                     checkClosed();