Synchronize access of current connections in JettyConnectionMetrics (#6587)

* JettyConnectionMetrics: synchronize access to connectionSamples (#6578)

Guard access to connectionSamples with connectionSamplesLock at all times.
This guarantees the gauge polls observe the number of current connections,
as intended.

Signed-off-by: Sergey Savenko <[email protected]>

* JettyConnectionMetrics: update maxConnections outside the critical section (#6578)

Move the update of the maxConnections TimeWindowMax out of the critical section

Signed-off-by: Sergey Savenko <[email protected]>

---------

Signed-off-by: Sergey Savenko <[email protected]>

Closes gh-6578

Author: deadok22

micrometer-core/src/main/java/io/micrometer/core/instrument/binder/jetty/JettyConnectionMetrics.java

@@ -121,7 +121,7 @@ public JettyConnectionMetrics(MeterRegistry registry, Iterable<Tag> tags) {
             .tags(tags)
             .register(registry);
 
-        Gauge.builder("jetty.connections.current", this, jcm -> jcm.connectionSamples.size())
+        Gauge.builder("jetty.connections.current", this, JettyConnectionMetrics::currentConnections)
             .strongReference(true)
             .baseUnit(BaseUnits.CONNECTIONS)
             .description("The current number of open Jetty connections")
@@ -160,10 +160,12 @@ private static Tags getConnectorNameTag(Connector connector) {
     @Override
     public void onOpened(Connection connection) {
         Timer.Sample started = Timer.start(registry);
+        int connections;
         synchronized (connectionSamplesLock) {
             connectionSamples.put(connection, started);
-            maxConnections.record(connectionSamples.size());
+            connections = connectionSamples.size();
         }
+        maxConnections.record(connections);
     }
 
     @Override
@@ -260,4 +262,10 @@ private static Method getNetworkTrafficListenerMethod(NetworkTrafficServerConnec
         return method;
     }
 
+    private int currentConnections() {
+        synchronized (connectionSamplesLock) {
+            return connectionSamples.size();
+        }
+    }
+
 }