switch from synchronized to ReentrantLock

build.gradle

@@ -1,6 +1,6 @@
 plugins {
   id 'com.github.ben-manes.versions' version '0.47.0'
-  id 'com.github.spotbugs' version '5.1.0' apply false
+  id 'com.github.spotbugs' version '5.1.3' apply false
   id 'me.champeau.jmh' version '0.7.1'
   id 'com.netflix.nebula.dependency-recommender' version '12.2.0'
   id 'com.netflix.nebula.netflixoss' version '11.3.2'

codequality/findbugs-exclude.xml

@@ -48,6 +48,12 @@
       <Bug pattern="IC_SUPERCLASS_USES_SUBCLASS_DURING_INITIALIZATION"/>
     </And>
   </Match>
+  <Match>
+    <And>
+      <Class name="com.netflix.spectator.atlas.impl.PrefixTree"/>
+      <Bug pattern="UL_UNRELEASED_LOCK"/>
+    </And>
+  </Match>
   <Match>
     <And>
       <Class name="com.netflix.spectator.perf.ManyTags"/>

spectator-api/src/main/java/com/netflix/spectator/api/CompositeRegistry.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2021 Netflix, Inc.
+ * Copyright 2014-2023 Netflix, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,6 +28,8 @@
 import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.concurrent.atomic.AtomicReference;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.function.BiFunction;
 import java.util.function.LongSupplier;
 
@@ -37,6 +39,8 @@
  */
 public final class CompositeRegistry implements Registry {
 
+  private final Lock lock = new ReentrantLock();
+
   private final Clock clock;
 
   private final AtomicReference<Registry[]> registries;
@@ -78,37 +82,52 @@ private int indexOf(Registry[] rs, Registry registry) {
   }
 
   /** Add a registry to the composite. */
-  public synchronized void add(Registry registry) {
-    Registry[] rs = registries.get();
-    int pos = indexOf(rs, registry);
-    if (pos == -1) {
-      Registry[] tmp = new Registry[rs.length + 1];
-      System.arraycopy(rs, 0, tmp, 0, rs.length);
-      tmp[rs.length] = registry;
-      registries.set(tmp);
-      version.incrementAndGet();
+  public void add(Registry registry) {
+    lock.lock();
+    try {
+      Registry[] rs = registries.get();
+      int pos = indexOf(rs, registry);
+      if (pos == -1) {
+        Registry[] tmp = new Registry[rs.length + 1];
+        System.arraycopy(rs, 0, tmp, 0, rs.length);
+        tmp[rs.length] = registry;
+        registries.set(tmp);
+        version.incrementAndGet();
+      }
+    } finally {
+      lock.unlock();
     }
   }
 
   /** Remove a registry from the composite. */
-  public synchronized void remove(Registry registry) {
-    Registry[] rs = registries.get();
-    int pos = indexOf(rs, registry);
-    if (pos >= 0) {
-      Registry[] tmp = new Registry[rs.length - 1];
-      if (pos > 0)
-        System.arraycopy(rs, 0, tmp, 0, pos);
-      if (pos < tmp.length)
-        System.arraycopy(rs, pos + 1, tmp, pos, rs.length - pos - 1);
-      registries.set(tmp);
-      version.incrementAndGet();
+  public void remove(Registry registry) {
+    lock.lock();
+    try {
+      Registry[] rs = registries.get();
+      int pos = indexOf(rs, registry);
+      if (pos >= 0) {
+        Registry[] tmp = new Registry[rs.length - 1];
+        if (pos > 0)
+          System.arraycopy(rs, 0, tmp, 0, pos);
+        if (pos < tmp.length)
+          System.arraycopy(rs, pos + 1, tmp, pos, rs.length - pos - 1);
+        registries.set(tmp);
+        version.incrementAndGet();
+      }
+    } finally {
+      lock.unlock();
     }
   }
 
   /** Remove all registries from the composite. */
-  public synchronized void removeAll() {
-    registries.set(new Registry[0]);
-    state.clear();
+  public void removeAll() {
+    lock.lock();
+    try {
+      registries.set(new Registry[0]);
+      state.clear();
+    } finally {
+      lock.unlock();
+    }
   }
 
   @Override public Clock clock() {

spectator-api/src/main/java/com/netflix/spectator/impl/Scheduler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2019 Netflix, Inc.
+ * Copyright 2014-2023 Netflix, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -33,6 +33,8 @@
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 
 /**
  * <p><b>This class is an internal implementation detail only intended for use within spectator.
@@ -113,6 +115,8 @@ private static Id newId(Registry registry, String id, String name) {
   private final ThreadFactory factory;
   private final Thread[] threads;
 
+  private final Lock lock = new ReentrantLock();
+
   private volatile boolean started = false;
   private volatile boolean shutdown = false;
 
@@ -168,26 +172,36 @@ public ScheduledFuture<?> schedule(Options options, Runnable task) {
    * Shutdown and cleanup resources associated with the scheduler. All threads will be
    * interrupted, but this method does not block for them to all finish execution.
    */
-  public synchronized void shutdown() {
-    shutdown = true;
-    for (int i = 0; i < threads.length; ++i) {
-      if (threads[i] != null && threads[i].isAlive()) {
-        threads[i].interrupt();
-        threads[i] = null;
+  public void shutdown() {
+    lock.lock();
+    try {
+      shutdown = true;
+      for (int i = 0; i < threads.length; ++i) {
+        if (threads[i] != null && threads[i].isAlive()) {
+          threads[i].interrupt();
+          threads[i] = null;
+        }
       }
+    } finally {
+      lock.unlock();
     }
   }
 
-  private synchronized void startThreads() {
-    if (!shutdown) {
-      started = true;
-      for (int i = 0; i < threads.length; ++i) {
-        if (threads[i] == null || !threads[i].isAlive() || threads[i].isInterrupted()) {
-          threads[i] = factory.newThread(new Worker());
-          threads[i].start();
-          LOGGER.debug("started thread {}", threads[i].getName());
+  private void startThreads() {
+    lock.lock();
+    try {
+      if (!shutdown) {
+        started = true;
+        for (int i = 0; i < threads.length; ++i) {
+          if (threads[i] == null || !threads[i].isAlive() || threads[i].isInterrupted()) {
+            threads[i] = factory.newThread(new Worker());
+            threads[i].start();
+            LOGGER.debug("started thread {}", threads[i].getName());
+          }
         }
       }
+    } finally {
+      lock.unlock();
     }
   }
 

spectator-ext-gc/src/main/java/com/netflix/spectator/gc/GcLogger.java

@@ -40,6 +40,8 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 
 /**
  * Logger to collect GC notifcation events.
@@ -82,6 +84,8 @@ public final class GcLogger {
   private static final Id CONCURRENT_PHASE_TIME =
       Spectator.globalRegistry().createId("jvm.gc.concurrentPhaseTime");
 
+  private final Lock lock = new ReentrantLock();
+
   private final long jvmStartTime;
 
   private final ConcurrentHashMap<String, CircularBuffer<GcEvent>> gcLogs = new ConcurrentHashMap<>();
@@ -129,38 +133,48 @@ public GcLogger() {
    *     If not null, the listener will be called with the event objects after metrics and the
    *     log buffer is updated.
    */
-  public synchronized void start(GcEventListener listener) {
-    // TODO: this class has a bad mix of static fields used from an instance of the class. For now
-    // this has been changed not to throw to make the dependency injection use-cases work. A
-    // more general refactor of the GcLogger class is needed.
-    if (notifListener != null) {
-      LOGGER.warn("logger already started");
-      return;
-    }
-    eventListener = listener;
-    notifListener = new GcNotificationListener();
-    for (GarbageCollectorMXBean mbean : ManagementFactory.getGarbageCollectorMXBeans()) {
-      if (mbean instanceof NotificationEmitter) {
-        final NotificationEmitter emitter = (NotificationEmitter) mbean;
-        emitter.addNotificationListener(notifListener, null, null);
+  public void start(GcEventListener listener) {
+    lock.lock();
+    try {
+      // TODO: this class has a bad mix of static fields used from an instance of the class. For now
+      // this has been changed not to throw to make the dependency injection use-cases work. A
+      // more general refactor of the GcLogger class is needed.
+      if (notifListener != null) {
+        LOGGER.warn("logger already started");
+        return;
       }
+      eventListener = listener;
+      notifListener = new GcNotificationListener();
+      for (GarbageCollectorMXBean mbean : ManagementFactory.getGarbageCollectorMXBeans()) {
+        if (mbean instanceof NotificationEmitter) {
+          final NotificationEmitter emitter = (NotificationEmitter) mbean;
+          emitter.addNotificationListener(notifListener, null, null);
+        }
+      }
+    } finally {
+      lock.unlock();
     }
   }
 
   /** Stop collecting GC events. */
-  public synchronized void stop() {
-    Preconditions.checkState(notifListener != null, "logger has not been started");
-    for (GarbageCollectorMXBean mbean : ManagementFactory.getGarbageCollectorMXBeans()) {
-      if (mbean instanceof NotificationEmitter) {
-        final NotificationEmitter emitter = (NotificationEmitter) mbean;
-        try {
-          emitter.removeNotificationListener(notifListener);
-        } catch (ListenerNotFoundException e) {
-          LOGGER.warn("could not remove gc listener", e);
+  public void stop() {
+    lock.lock();
+    try {
+      Preconditions.checkState(notifListener != null, "logger has not been started");
+      for (GarbageCollectorMXBean mbean : ManagementFactory.getGarbageCollectorMXBeans()) {
+        if (mbean instanceof NotificationEmitter) {
+          final NotificationEmitter emitter = (NotificationEmitter) mbean;
+          try {
+            emitter.removeNotificationListener(notifListener);
+          } catch (ListenerNotFoundException e) {
+            LOGGER.warn("could not remove gc listener", e);
+          }
         }
       }
+      notifListener = null;
+    } finally {
+      lock.unlock();
     }
-    notifListener = null;
   }
 
   /** Return the current set of GC events in the in-memory log. */

spectator-ext-ipc/src/main/java/com/netflix/spectator/ipc/http/HttpRequestBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2020 Netflix, Inc.
+ * Copyright 2014-2023 Netflix, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -42,6 +42,8 @@
 import java.util.concurrent.Executors;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.function.Consumer;
 import java.util.function.Supplier;
 import java.util.zip.Deflater;
@@ -60,6 +62,8 @@ public class HttpRequestBuilder {
 
   private static final StreamHelper STREAM_HELPER = new StreamHelper();
 
+  private static final Lock LOCK = new ReentrantLock();
+
   // Should not be used directly, use the method of the same name that will create the
   // executor if needed on the first access.
   private static volatile ExecutorService defaultExecutor;
@@ -82,10 +86,13 @@ private static ExecutorService defaultExecutor() {
     if (executor != null) {
       return executor;
     }
-    synchronized (LOGGER) {
+    LOCK.lock();
+    try {
       defaultExecutor = Executors.newFixedThreadPool(
           Runtime.getRuntime().availableProcessors(), newThreadFactory());
       return defaultExecutor;
+    } finally {
+      LOCK.unlock();
     }
   }