2 files changed, 24 insertions, 10 deletions

diff --git a/spark-common/src/main/java/me/lucko/spark/sampler/ThreadDumper.java b/spark-common/src/main/java/me/lucko/spark/sampler/ThreadDumper.java
index 61706f4..38cdd36 100644
--- a/spark-common/src/main/java/me/lucko/spark/sampler/ThreadDumper.java
+++ b/spark-common/src/main/java/me/lucko/spark/sampler/ThreadDumper.java
@@ -21,11 +21,13 @@
 
 package me.lucko.spark.sampler;
 
-import me.lucko.spark.util.Threads;
+import me.lucko.spark.util.ThreadFinder;
 
 import java.lang.management.ThreadInfo;
 import java.lang.management.ThreadMXBean;
 import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
 import java.util.regex.Pattern;
@@ -56,6 +58,7 @@ public interface ThreadDumper {
      * Implementation of {@link ThreadDumper} that generates data for a specific set of threads.
      */
     final class Specific implements ThreadDumper {
+        private final ThreadFinder threadFinder = new ThreadFinder();
         private final long[] ids;
 
         public Specific(long[] ids) {
@@ -64,7 +67,7 @@ public interface ThreadDumper {
 
         public Specific(Set<String> names) {
             Set<String> namesLower = names.stream().map(String::toLowerCase).collect(Collectors.toSet());
-            this.ids = Threads.getThreads()
+            this.ids = this.threadFinder.getThreads()
                     .filter(t -> namesLower.contains(t.getName().toLowerCase()))
                     .mapToLong(Thread::getId)
                     .toArray();
@@ -80,7 +83,9 @@ public interface ThreadDumper {
      * Implementation of {@link ThreadDumper} that generates data for a regex matched set of threads.
      */
     final class Regex implements ThreadDumper {
+        private final ThreadFinder threadFinder = new ThreadFinder();
         private final Set<Pattern> namePatterns;
+        private final Map<Long, Boolean> cache = new HashMap<>();
 
         public Regex(Set<String> namePatterns) {
             this.namePatterns = namePatterns.stream()
@@ -97,13 +102,20 @@ public interface ThreadDumper {
 
         @Override
         public Iterable<ThreadInfo> dumpThreads(ThreadMXBean threadBean) {
-            return Threads.getThreads()
+            return this.threadFinder.getThreads()
                     .filter(thread -> {
+                        Boolean result = this.cache.get(thread.getId());
+                        if (result != null) {
+                            return result;
+                        }
+
                         for (Pattern pattern : this.namePatterns) {
                             if (pattern.matcher(thread.getName()).matches()) {
+                                this.cache.put(thread.getId(), true);
                                 return true;
                             }
                         }
+                        this.cache.put(thread.getId(), false);
                         return false;
                     })
                     .map(thread -> threadBean.getThreadInfo(thread.getId()))
diff --git a/spark-common/src/main/java/me/lucko/spark/util/Threads.java b/spark-common/src/main/java/me/lucko/spark/util/ThreadFinder.java
index d1efdff..a74f85a 100644
--- a/spark-common/src/main/java/me/lucko/spark/util/Threads.java
+++ b/spark-common/src/main/java/me/lucko/spark/util/ThreadFinder.java
@@ -25,14 +25,11 @@ import java.util.Objects;
 import java.util.stream.Stream;
 
 /**
- * Utilities for working with {@link Thread}s.
+ * Utility to find active threads.
  */
-public final class Threads {
-
-    private Threads() {}
+public final class ThreadFinder {
 
     private static final ThreadGroup ROOT_THREAD_GROUP;
-
     static {
         ThreadGroup rootGroup = Thread.currentThread().getThreadGroup();
         ThreadGroup parentGroup;
@@ -42,13 +39,18 @@ public final class Threads {
         ROOT_THREAD_GROUP = rootGroup;
     }
 
+    // cache the approx active count at the time of construction.
+    // the usages of this class are likely to be somewhat short-lived, so it's good
+    // enough to just cache a value on init.
+    private final int approxActiveCount = ROOT_THREAD_GROUP.activeCount();
+
     /**
      * Gets a stream of all known active threads.
      *
      * @return a stream of threads
      */
-    public static Stream<Thread> getThreads() {
-        Thread[] threads = new Thread[ROOT_THREAD_GROUP.activeCount()];
+    public Stream<Thread> getThreads() {
+        Thread[] threads = new Thread[this.approxActiveCount + 20]; // +20 to allow a bit of growth for newly created threads
         while (ROOT_THREAD_GROUP.enumerate(threads, true ) == threads.length) {
             threads = new Thread[threads.length * 2];
         }