Fix bug where hot threads did not work with duplicate names / add thread_id

The hot threads endpoint used to require thread names to be unique in a map and would crash otherwise. This patch fixes this by internally using a List instead of a Map to store these thread ids.

Additionally, this patch adds the `thread_id` to the response to allow for disambiguation of of threads for any client applications.

Fixes https://github.com/elastic/logstash/issues/7608

Fixes #7617

logstash-core/lib/logstash/api/commands/hot_threads_reporter.rb

@@ -17,7 +17,12 @@ class HotThreadsReport
     report << '=' * STRING_SEPARATOR_LENGTH
     report << "\n"
     hash[:threads].each do |thread|
-      thread_report = "#{I18n.t("logstash.web_api.hot_threads.thread_title", :percent_of_cpu_time => thread[:percent_of_cpu_time], :thread_state => thread[:state], :thread_name => thread[:name])} \n"
+      line_str = I18n.t("logstash.web_api.hot_threads.thread_title", 
+        :percent_of_cpu_time => thread[:percent_of_cpu_time], 
+        :thread_state => thread[:state], 
+        :thread_name => thread[:name],
+        :thread_id => thread[:thread_id])
+      thread_report = "#{line_str} \n"
       thread_report << "#{thread[:path]}\n" if thread[:path]
       thread[:traces].each do |trace|
         thread_report << "\t#{trace}\n"
@@ -31,9 +36,10 @@ class HotThreadsReport
 
   def to_hash
     hash = { :time => Time.now.iso8601, :busiest_threads => @thread_dump.top_count, :threads => [] }
-    @thread_dump.each do |thread_name, _hash|
+    @thread_dump.each do |_hash|
       thread_name, thread_path = _hash["thread.name"].split(": ")
       thread = { :name => thread_name,
+                 :thread_id => _hash["thread.id"],
                  :percent_of_cpu_time => cpu_time_as_percent(_hash),
                  :state => _hash["thread.state"]
       }

logstash-core/lib/logstash/util/thread_dump.rb

@@ -19,12 +19,13 @@ module LogStash
 
       def each(&block)
         i=0
-        dump.each_pair do |thread_name, _hash|
+        dump.each do |hash|
+          thread_name = hash["thread.name"]
           break if i >= top_count
           if ignore
-            next if idle_thread?(thread_name, _hash)
+            next if idle_thread?(thread_name, hash)
           end
-          block.call(thread_name, _hash)
+          block.call(hash)
           i += 1
         end
       end

logstash-core/locales/en.yml

@@ -81,7 +81,7 @@ en:
           ::: {%{hostname}}
           Hot threads at %{time}, busiestThreads=%{top_count}:
         thread_title: |-
-          %{percent_of_cpu_time} % of cpu usage, state: %{thread_state}, thread name: '%{thread_name}'
+          %{percent_of_cpu_time} % of cpu usage, state: %{thread_state}, thread name: '%{thread_name}', thread id: %{thread_id}
       logging:
         unrecognized_option: |-
           unrecognized option [%{option}]

logstash-core/src/main/java/org/logstash/instrument/monitors/HotThreadsMonitor.java

@@ -43,6 +43,7 @@ public final class HotThreadsMonitor {
         private static final String THREAD_NAME = "thread.name";
         private static final String THREAD_STATE = "thread.state";
         private static final String THREAD_STACKTRACE = "thread.stacktrace";
+        private static final String THREAD_ID = "thread.id";
 
         private Map<String, Object> map = new HashMap<>();
 
@@ -53,6 +54,7 @@ public final class HotThreadsMonitor {
             map.put(WAITED_COUNT, info.getWaitedCount());
             map.put(WAITED_TIME, info.getWaitedTime());
             map.put(THREAD_NAME, info.getThreadName());
+            map.put(THREAD_ID, info.getThreadId());
             map.put(THREAD_STATE, info.getThreadState().name().toLowerCase());
             map.put(THREAD_STACKTRACE, stackTraceAsString(info.getStackTrace()));
         }
@@ -71,6 +73,10 @@ public final class HotThreadsMonitor {
             return (String) map.get(THREAD_NAME);
         }
 
+        public long getThreadId() {
+            return (long) map.get(THREAD_ID);
+        }
+
         @Override
         public String toString() {
             StringBuilder sb = new StringBuilder();

logstash-core/src/main/java/org/logstash/instrument/reports/ThreadsReport.java

@@ -21,13 +21,12 @@ public class ThreadsReport {
      *                      stacktrace_size - max depth of stack trace
      * @return A Map containing hot threads information
      */
-    public static Map<String, Object> generate(Map<String, String> options) {
+    public static List<Map<String, Object>> generate(Map<String, String> options) {
         List<HotThreadsMonitor.ThreadReport> reports = HotThreadsMonitor.detect(options);
         return reports
                 .stream()
-                .collect(Collectors
-                    .toMap(HotThreadsMonitor.ThreadReport::getThreadName,
-                           HotThreadsMonitor.ThreadReport::toMap));
+                .map(HotThreadsMonitor.ThreadReport::toMap)
+                .collect(Collectors.toList());
     }
 
 
@@ -35,7 +34,7 @@ public class ThreadsReport {
      * Generate a report with current Thread information
      * @return A Map containing the hot threads information
      */
-    public static Map<String, Object> generate() {
+    public static List<Map<String, Object>> generate() {
         Map<String, String> options = new HashMap<>();
         options.put("order_by", "cpu");
         return generate(options);