Fix collection concurrency

core/src/main/java/org/apache/accumulo/core/clientImpl/TabletServerBatchReaderIterator.java

@@ -395,11 +395,8 @@ public void run() {
       Map<KeyExtent,List<Range>> unscanned = new HashMap<>();
       Map<KeyExtent,List<Range>> tsFailures = new HashMap<>();
       try {
-        TimeoutTracker timeoutTracker = timeoutTrackers.get(tsLocation);
-        if (timeoutTracker == null) {
-          timeoutTracker = new TimeoutTracker(tsLocation, timedoutServers, retryTimeout);
-          timeoutTrackers.put(tsLocation, timeoutTracker);
-        }
+        TimeoutTracker timeoutTracker = timeoutTrackers.computeIfAbsent(tsLocation,
+            key -> new TimeoutTracker(key, timedoutServers, retryTimeout));
         doLookup(context, tsLocation, tabletsRanges, tsFailures, unscanned, receiver, columns,
             options, authorizations, timeoutTracker, busyTimeout);
 

core/src/main/java/org/apache/accumulo/core/clientImpl/TabletServerBatchWriter.java

@@ -872,11 +872,8 @@ public void send(TabletServerMutations<Mutation> tsm)
           Span span = TraceUtil.startSpan(this.getClass(), "sendMutations");
           try (Scope scope = span.makeCurrent()) {
 
-            TimeoutTracker timeoutTracker = timeoutTrackers.get(location);
-            if (timeoutTracker == null) {
-              timeoutTracker = new TimeoutTracker(location, timeout);
-              timeoutTrackers.put(location, timeoutTracker);
-            }
+            TimeoutTracker timeoutTracker =
+                timeoutTrackers.computeIfAbsent(location, l -> new TimeoutTracker(l, timeout));
 
             long st1 = System.currentTimeMillis();
             try (SessionCloser sessionCloser = new SessionCloser(location)) {

core/src/main/java/org/apache/accumulo/core/conf/ConfigurationCopy.java

@@ -39,7 +39,7 @@ public class ConfigurationCopy extends AccumuloConfiguration {
    * @param config configuration property key/value pairs to copy
    */
   public ConfigurationCopy(Map<String,String> config) {
-    this(config.entrySet());
+    copy.putAll(config);
   }
 
   /**
@@ -74,11 +74,11 @@ public String get(Property property) {
 
   @Override
   public void getProperties(Map<String,String> props, Predicate<String> filter) {
-    for (Entry<String,String> entry : copy.entrySet()) {
-      if (filter.test(entry.getKey())) {
-        props.put(entry.getKey(), entry.getValue());
+    copy.forEach((key, value) -> {
+      if (filter.test(key)) {
+        props.put(key, value);
       }
-    }
+    });
   }
 
   /**

core/src/main/java/org/apache/accumulo/core/iteratorsImpl/system/StatsIterator.java

@@ -94,9 +94,7 @@ public void report(boolean reportDeepCopies) {
 
     if (reportDeepCopies) {
       // recurse down the fat tree of deep copies forcing them to report
-      for (var deepCopy : deepCopies) {
-        deepCopy.report(true);
-      }
+      deepCopies.forEach(deepCopy -> deepCopy.report(true));
     }
   }
 }

server/base/src/main/java/org/apache/accumulo/server/compaction/FileCompactor.java

@@ -265,11 +265,7 @@ private static void updateTotalEntries() {
   public static List<CompactionInfo> getRunningCompactions() {
     ArrayList<CompactionInfo> compactions = new ArrayList<>();
 
-    synchronized (runningCompactions) {
-      for (FileCompactor compactor : runningCompactions) {
-        compactions.add(new CompactionInfo(compactor));
-      }
-    }
+    runningCompactions.forEach(compactor -> compactions.add(new CompactionInfo(compactor)));
 
     return compactions;
   }

server/monitor/src/main/java/org/apache/accumulo/monitor/Monitor.java

@@ -158,6 +158,12 @@ public boolean add(Pair<Long,T> obj) {
     });
   }
 
+  private static <T> List<T> snapshotSynchronizedList(List<T> list) {
+    synchronized (list) {
+      return new ArrayList<>(list);
+    }
+  }
+
   private final List<Pair<Long,Double>> loadOverTime = newMaxList();
   private final List<Pair<Long,Double>> ingestRateOverTime = newMaxList();
   private final List<Pair<Long,Double>> ingestByteRateOverTime = newMaxList();
@@ -938,51 +944,51 @@ public long getStartTime() {
   }
 
   public List<Pair<Long,Double>> getLoadOverTime() {
-    return new ArrayList<>(loadOverTime);
+    return snapshotSynchronizedList(loadOverTime);
   }
 
   public List<Pair<Long,Double>> getIngestRateOverTime() {
-    return new ArrayList<>(ingestRateOverTime);
+    return snapshotSynchronizedList(ingestRateOverTime);
   }
 
   public List<Pair<Long,Double>> getIngestByteRateOverTime() {
-    return new ArrayList<>(ingestByteRateOverTime);
+    return snapshotSynchronizedList(ingestByteRateOverTime);
   }
 
   public List<Pair<Long,Integer>> getMinorCompactionsOverTime() {
-    return new ArrayList<>(minorCompactionsOverTime);
+    return snapshotSynchronizedList(minorCompactionsOverTime);
   }
 
   public List<Pair<Long,Integer>> getMajorCompactionsOverTime() {
-    return new ArrayList<>(majorCompactionsOverTime);
+    return snapshotSynchronizedList(majorCompactionsOverTime);
   }
 
   public List<Pair<Long,Double>> getLookupsOverTime() {
-    return new ArrayList<>(lookupsOverTime);
+    return snapshotSynchronizedList(lookupsOverTime);
   }
 
   public double getLookupRate() {
     return lookupRateTracker.calculateRate();
   }
 
   public List<Pair<Long,Long>> getQueryRateOverTime() {
-    return new ArrayList<>(queryRateOverTime);
+    return snapshotSynchronizedList(queryRateOverTime);
   }
 
   public List<Pair<Long,Long>> getScanRateOverTime() {
-    return new ArrayList<>(scanRateOverTime);
+    return snapshotSynchronizedList(scanRateOverTime);
   }
 
   public List<Pair<Long,Double>> getQueryByteRateOverTime() {
-    return new ArrayList<>(queryByteRateOverTime);
+    return snapshotSynchronizedList(queryByteRateOverTime);
   }
 
   public List<Pair<Long,Double>> getIndexCacheHitRateOverTime() {
-    return new ArrayList<>(indexCacheHitRateOverTime);
+    return snapshotSynchronizedList(indexCacheHitRateOverTime);
   }
 
   public List<Pair<Long,Double>> getDataCacheHitRateOverTime() {
-    return new ArrayList<>(dataCacheHitRateOverTime);
+    return snapshotSynchronizedList(dataCacheHitRateOverTime);
   }
 
   @Override

start/src/main/java/org/apache/accumulo/start/classloader/vfs/AccumuloVFSClassLoader.java

@@ -89,7 +89,7 @@ public void run() {
 
   }
 
-  private static List<WeakReference<DefaultFileSystemManager>> vfsInstances =
+  private static final List<WeakReference<DefaultFileSystemManager>> vfsInstances =
       Collections.synchronizedList(new ArrayList<>());
 
   public static final String DYNAMIC_CLASSPATH_PROPERTY_NAME = "general.dynamic.classpaths";
@@ -440,7 +440,7 @@ public static synchronized ContextManager getContextManager() throws IOException
   }
 
   public static void close() {
-    for (WeakReference<DefaultFileSystemManager> vfsInstance : vfsInstances) {
+    vfsInstances.forEach(vfsInstance -> {
       DefaultFileSystemManager ref = vfsInstance.get();
       if (ref != null) {
         FileReplicator replicator;
@@ -454,7 +454,7 @@ public static void close() {
         }
         ref.close();
       }
-    }
+    });
     try {
       FileUtils.deleteDirectory(computeTopCacheDir());
     } catch (IOException e) {