Change synchronized on FileSystemContext to avoid deadlock

### What changes are proposed in this pull request?

Please outline the changes and how this PR fixes the issue.

### Why are the changes needed?

Please clarify why the changes are needed. For instance,
1. If you propose a new API, clarify the use case for a new API.
2. If you fix a bug, describe the bug.

### Does this PR introduce any user facing changes?

Please list the user-facing changes introduced by your change, including
1. change in user-facing APIs
2. addition or removal of property keys
3. webui

pr-link: Alluxio#16219
change-id: cid-f6e6af4556026e122b2e672fad6ab87a0a9f507e

Author: elega

core/client/fs/src/main/java/alluxio/client/file/FileSystemContext.java

@@ -62,6 +62,7 @@
 import java.util.Optional;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.GuardedBy;
 import javax.annotation.concurrent.ThreadSafe;
@@ -162,11 +163,11 @@ public class FileSystemContext implements Closeable {
   private MetadataCache mMetadataCache;
 
   /** Cached map for workers. */
-  @GuardedBy("this")
-  private volatile List<BlockWorkerInfo> mWorkerInfoList = null;
+  @GuardedBy("mWorkerInfoList")
+  private final AtomicReference<List<BlockWorkerInfo>> mWorkerInfoList = new AtomicReference<>();
 
   /** The policy to refresh workers list. */
-  @GuardedBy("this")
+  @GuardedBy("mWorkerInfoList")
   private final RefreshPolicy mWorkerRefreshPolicy;
 
   /**
@@ -651,11 +652,14 @@ public synchronized WorkerNetAddress getNodeLocalWorker() throws IOException {
    *
    * @return the info of all block workers eligible for reads and writes
    */
-  public synchronized List<BlockWorkerInfo> getCachedWorkers() throws IOException {
-    if (mWorkerInfoList == null || mWorkerInfoList.isEmpty() || mWorkerRefreshPolicy.attempt()) {
-      mWorkerInfoList = getAllWorkers();
+  public List<BlockWorkerInfo> getCachedWorkers() throws IOException {
+    synchronized (mWorkerInfoList) {
+      if (mWorkerInfoList.get() == null || mWorkerInfoList.get().isEmpty()
+          || mWorkerRefreshPolicy.attempt()) {
+        mWorkerInfoList.set(getAllWorkers());
+      }
+      return mWorkerInfoList.get();
     }
-    return mWorkerInfoList;
   }
 
   /**