[
https://issues.apache.org/jira/browse/HBASE-29804?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
ConfX updated HBASE-29804:
--------------------------
Description:
h2. Summary
`WorkerAssigner.serverAdded()` throws NullPointerException when called during
or after Master shutdown because it accesses `MasterProcedureExecutor` without
null checks, but `MasterProcedureExecutor` is explicitly set to null during the
shutdown process.
h2. Affected Component
- *{*}File:{*}*
`hbase-server/src/main/java/org/apache/hadoop/hbase/master/WorkerAssigner.java`
- *{*}Method:{*}* `serverAdded(ServerName worker)` at line 83
h2. Root Cause Analysis
h3. The Bug
The `WorkerAssigner` class implements `ServerListener` and registers itself
with `ServerManager` to receive server event notifications. In the
`serverAdded()` callback method, it accesses a chain of objects without null
checks:
{code:java}
@Override
public void serverAdded(ServerName worker) {
this.wake(master.getMasterProcedureExecutor().getEnvironment().getProcedureScheduler());
}{code}
h3. Why NPE Occurs
During Master shutdown, the `procedureExecutor` is explicitly set to `null` in
`HMaster.stopProcedureExecutor()`:
{code:java}
// HMaster.java:1849-1856
private void stopProcedureExecutor() {
if (procedureExecutor != null) {
configurationManager.deregisterObserver(procedureExecutor.getEnvironment());
procedureExecutor.getEnvironment().getRemoteDispatcher().stop();
procedureExecutor.stop();
procedureExecutor.join();
procedureExecutor = null; // <-- Set to null here
}
// ...
}{code}
However, `WorkerAssigner` is *{*}never unregistered{*}* from `ServerManager`
during shutdown. If any `serverAdded()` event is triggered during or after the
shutdown process (while `WorkerAssigner` is still registered as a listener), it
will cause an NPE because `getMasterProcedureExecutor()` returns `null`.
h3. Call Chain When Failure Occurs
1. `ServerManager.regionServerReport()` (line 295)
2. `ServerManager.checkAndRecordNewServer()` (line 377)
3. `ServerListener.serverAdded()` callback for all registered listeners
4. `WorkerAssigner.serverAdded()` (line 83) - *{*}NPE occurs here{*}*
h3. Stacktrace
{code:java}
java.lang.NullPointerException
at
org.apache.hadoop.hbase.master.WorkerAssigner.serverAdded(WorkerAssigner.java:83)
at
org.apache.hadoop.hbase.master.ServerManager.checkAndRecordNewServer(ServerManager.java:377)
at
org.apache.hadoop.hbase.master.ServerManager.regionServerReport(ServerManager.java:295)
at
org.apache.hadoop.hbase.master.MasterRpcServices.regionServerReport(MasterRpcServices.java:573)
{code}
h3. Potential Fix
h4. Option 1: Add Null Check in serverAdded() (Recommended)
{code:java}
@Override
public void serverAdded(ServerName worker) {
ProcedureExecutor<MasterProcedureEnv> executor =
master.getMasterProcedureExecutor();
if (executor != null && executor.getEnvironment() != null) {
this.wake(executor.getEnvironment().getProcedureScheduler());
}
} {code}
h3. Option 2: Unregister WorkerAssigner During Shutdown
Add a `close()` or `stop()` method to `WorkerAssigner` that unregisters it from
`ServerManager`, and call it during master shutdown in `SplitWALManager` and
`SnapshotManager`.
{code:java}
public void stop() {
ServerManager sm = this.master.getServerManager();
if (sm != null) {
sm.unregisterListener(this);
}
} {code}
h3. Option 3: Both (Most Robust)
Implement both the null check (defensive programming) AND proper unregistration
(proper lifecycle management).
was:
h2. Summary
`WorkerAssigner.serverAdded()` throws NullPointerException when called during
or after Master shutdown because it accesses `MasterProcedureExecutor` without
null checks, but `MasterProcedureExecutor` is explicitly set to null during the
shutdown process.
h2. Affected Component
- **File:**
`hbase-server/src/main/java/org/apache/hadoop/hbase/master/WorkerAssigner.java`
- **Method:** `serverAdded(ServerName worker)` at line 83
h2. Root Cause Analysis
h3. The Bug
The `WorkerAssigner` class implements `ServerListener` and registers itself
with `ServerManager` to receive server event notifications. In the
`serverAdded()` callback method, it accesses a chain of objects without null
checks:
{code:java}
@Override
public void serverAdded(ServerName worker) {
this.wake(master.getMasterProcedureExecutor().getEnvironment().getProcedureScheduler());
}{code}
h3. Why NPE Occurs
During Master shutdown, the `procedureExecutor` is explicitly set to `null` in
`HMaster.stopProcedureExecutor()`:
{code:java}
// HMaster.java:1849-1856
private void stopProcedureExecutor() {
if (procedureExecutor != null) {
configurationManager.deregisterObserver(procedureExecutor.getEnvironment());
procedureExecutor.getEnvironment().getRemoteDispatcher().stop();
procedureExecutor.stop();
procedureExecutor.join();
procedureExecutor = null; // <-- Set to null here
}
// ...
}{code}
However, `WorkerAssigner` is **never unregistered** from `ServerManager` during
shutdown. If any `serverAdded()` event is triggered during or after the
shutdown process (while `WorkerAssigner` is still registered as a listener), it
will cause an NPE because `getMasterProcedureExecutor()` returns `null`.
h3. Call Chain When Failure Occurs
1. `ServerManager.regionServerReport()` (line 295)
2. `ServerManager.checkAndRecordNewServer()` (line 377)
3. `ServerListener.serverAdded()` callback for all registered listeners
4. `WorkerAssigner.serverAdded()` (line 83) - **NPE occurs here**
## Stacktrace
{code:java}
java.lang.NullPointerException
at
org.apache.hadoop.hbase.master.WorkerAssigner.serverAdded(WorkerAssigner.java:83)
at
org.apache.hadoop.hbase.master.ServerManager.checkAndRecordNewServer(ServerManager.java:377)
at
org.apache.hadoop.hbase.master.ServerManager.regionServerReport(ServerManager.java:295)
at
org.apache.hadoop.hbase.master.MasterRpcServices.regionServerReport(MasterRpcServices.java:573)
{code}
h3. Potential Fix
h4. Option 1: Add Null Check in serverAdded() (Recommended)
{code:java}
@Override
public void serverAdded(ServerName worker) {
ProcedureExecutor<MasterProcedureEnv> executor =
master.getMasterProcedureExecutor();
if (executor != null && executor.getEnvironment() != null) {
this.wake(executor.getEnvironment().getProcedureScheduler());
}
} {code}
h3. Option 2: Unregister WorkerAssigner During Shutdown
Add a `close()` or `stop()` method to `WorkerAssigner` that unregisters it from
`ServerManager`, and call it during master shutdown in `SplitWALManager` and
`SnapshotManager`.
{code:java}
public void stop() {
ServerManager sm = this.master.getServerManager();
if (sm != null) {
sm.unregisterListener(this);
}
} {code}
h3. Option 3: Both (Most Robust)
Implement both the null check (defensive programming) AND proper unregistration
(proper lifecycle management).
> NullPointerException in WorkerAssigner.serverAdded during Master Shutdown and
> Restart
> -------------------------------------------------------------------------------------
>
> Key: HBASE-29804
> URL: https://issues.apache.org/jira/browse/HBASE-29804
> Project: HBase
> Issue Type: Bug
> Components: master
> Affects Versions: 2.6.3, 2.6.4
> Reporter: ConfX
> Priority: Major
>
> h2. Summary
>
> `WorkerAssigner.serverAdded()` throws NullPointerException when called during
> or after Master shutdown because it accesses `MasterProcedureExecutor`
> without null checks, but `MasterProcedureExecutor` is explicitly set to null
> during the shutdown process.
> h2. Affected Component
> - *{*}File:{*}*
> `hbase-server/src/main/java/org/apache/hadoop/hbase/master/WorkerAssigner.java`
> - *{*}Method:{*}* `serverAdded(ServerName worker)` at line 83
> h2. Root Cause Analysis
> h3. The Bug
>
> The `WorkerAssigner` class implements `ServerListener` and registers itself
> with `ServerManager` to receive server event notifications. In the
> `serverAdded()` callback method, it accesses a chain of objects without null
> checks:
> {code:java}
> @Override
> public void serverAdded(ServerName worker) {
>
> this.wake(master.getMasterProcedureExecutor().getEnvironment().getProcedureScheduler());
> }{code}
> h3. Why NPE Occurs
> During Master shutdown, the `procedureExecutor` is explicitly set to `null`
> in `HMaster.stopProcedureExecutor()`:
> {code:java}
> // HMaster.java:1849-1856
> private void stopProcedureExecutor() {
> if (procedureExecutor != null) {
>
> configurationManager.deregisterObserver(procedureExecutor.getEnvironment());
> procedureExecutor.getEnvironment().getRemoteDispatcher().stop();
> procedureExecutor.stop();
> procedureExecutor.join();
> procedureExecutor = null; // <-- Set to null here
> }
> // ...
> }{code}
> However, `WorkerAssigner` is *{*}never unregistered{*}* from `ServerManager`
> during shutdown. If any `serverAdded()` event is triggered during or after
> the shutdown process (while `WorkerAssigner` is still registered as a
> listener), it will cause an NPE because `getMasterProcedureExecutor()`
> returns `null`.
> h3. Call Chain When Failure Occurs
> 1. `ServerManager.regionServerReport()` (line 295)
> 2. `ServerManager.checkAndRecordNewServer()` (line 377)
> 3. `ServerListener.serverAdded()` callback for all registered listeners
> 4. `WorkerAssigner.serverAdded()` (line 83) - *{*}NPE occurs here{*}*
>
> h3. Stacktrace
> {code:java}
> java.lang.NullPointerException
> at
> org.apache.hadoop.hbase.master.WorkerAssigner.serverAdded(WorkerAssigner.java:83)
> at
> org.apache.hadoop.hbase.master.ServerManager.checkAndRecordNewServer(ServerManager.java:377)
> at
> org.apache.hadoop.hbase.master.ServerManager.regionServerReport(ServerManager.java:295)
> at
> org.apache.hadoop.hbase.master.MasterRpcServices.regionServerReport(MasterRpcServices.java:573)
> {code}
>
> h3. Potential Fix
> h4. Option 1: Add Null Check in serverAdded() (Recommended)
>
> {code:java}
> @Override
> public void serverAdded(ServerName worker) {
> ProcedureExecutor<MasterProcedureEnv> executor =
> master.getMasterProcedureExecutor();
> if (executor != null && executor.getEnvironment() != null) {
> this.wake(executor.getEnvironment().getProcedureScheduler());
> }
> } {code}
> h3. Option 2: Unregister WorkerAssigner During Shutdown
>
> Add a `close()` or `stop()` method to `WorkerAssigner` that unregisters it
> from `ServerManager`, and call it during master shutdown in `SplitWALManager`
> and `SnapshotManager`.
>
>
> {code:java}
> public void stop() {
> ServerManager sm = this.master.getServerManager();
> if (sm != null) {
> sm.unregisterListener(this);
> }
> } {code}
> h3. Option 3: Both (Most Robust)
> Implement both the null check (defensive programming) AND proper
> unregistration (proper lifecycle management).
>
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