From 064974fdd5217838780f521ca27cea810b5bb315 Mon Sep 17 00:00:00 2001
From: xirtameht <59612894+xirtameht@users.noreply.github.com>
Date: Wed, 6 Oct 2021 08:25:09 -0400
Subject: [PATCH] Added HighCycleThrottler class to mitigate high cpu load
 defect.

---
 .../server/HighCycleThrottler.java            | 69 +++++++++++++++++++
 .../server/WebSocketServer.java               |  2 +
 2 files changed, 71 insertions(+)
 create mode 100644 src/main/java/org/java_websocket/server/HighCycleThrottler.java

diff --git a/src/main/java/org/java_websocket/server/HighCycleThrottler.java b/src/main/java/org/java_websocket/server/HighCycleThrottler.java
new file mode 100644
index 00000000..dc858cdb
--- /dev/null
+++ b/src/main/java/org/java_websocket/server/HighCycleThrottler.java
@@ -0,0 +1,69 @@
+package org.java_websocket.server;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * <tt>HighCycleThrottler</tt> is a class that checks for high cycling caused by the jdk epoll selector bug.  For some
+ * reason the selector.select() code becomes not blocking causing a high CPU condition.  When this condition is detected,
+ * this class will add a 1ms delay to keep from loading up the CPU when the selector.select() code is no longer blocking.
+ *  */
+public class HighCycleThrottler
+{
+   private final Logger log = LoggerFactory.getLogger( HighCycleThrottler.class );
+   private static final int CYCLE_THRESHOLD = 600 * 60;  // 600 cycles a second for 60 seconds;
+   private final boolean  enabled;
+   private long nextCycle;
+   private long cyclesPerMinute = 0;
+   private boolean highCPUDetected = false;
+
+   public HighCycleThrottler() {
+      enabled = isEnabled( );
+      nextCycle = System.currentTimeMillis() + 60 * 1000;
+   }
+
+   /**
+    * Checks for high cycling and throttles with a 1ms delay if detected.
+    */
+   public void checkHighCycleRate() {
+      if ( enabled ) {
+         cyclesPerMinute++;
+         if ( System.currentTimeMillis() >= nextCycle ) {
+            String cycles = String.format( "Cycles last minute = %d", cyclesPerMinute );
+            log.warn( cycles );
+
+            if ( cyclesPerMinute > CYCLE_THRESHOLD ){
+             if( !highCPUDetected ){
+                  highCPUDetected = true;
+                  log.warn( "High CPU condition detected" );
+               }
+            } else if ( highCPUDetected ) {
+               log.warn( "High CPU condition cleared" );
+               highCPUDetected = false;
+            }
+
+            nextCycle = System.currentTimeMillis() + 60 * 1000;
+            cyclesPerMinute = 0;
+         }
+
+         if ( highCPUDetected ) {
+            try {
+               Thread.sleep( 1L );
+            } catch ( InterruptedException e ) {
+               log.warn( "Thread.sleep(1L) failed" );
+            }
+         }
+      }
+   }
+
+   /**
+    * Set the enabled flag and log if USE_EPOLL_SELECTOR_FIX is defined.
+    */
+   private boolean isEnabled() {
+      if (System.getenv( "USE_EPOLL_SELECTOR_FIX" ) != null){
+         log.warn( "Using EPoll Selector Fix" );
+         return true;
+      }
+      return false;
+   }
+}
diff --git a/src/main/java/org/java_websocket/server/WebSocketServer.java b/src/main/java/org/java_websocket/server/WebSocketServer.java
index 11073619..769610e8 100644
--- a/src/main/java/org/java_websocket/server/WebSocketServer.java
+++ b/src/main/java/org/java_websocket/server/WebSocketServer.java
@@ -362,6 +362,7 @@ public void run() {
     if (!doSetupSelectorAndServerThread()) {
       return;
     }
+    HighCycleThrottler highCycleThrottler = new HighCycleThrottler();
     try {
       int shutdownCount = 5;
       int selectTimeout = 0;
@@ -411,6 +412,7 @@ public void run() {
           // FIXME controlled shutdown (e.g. take care of buffermanagement)
           Thread.currentThread().interrupt();
         }
+        highCycleThrottler.checkHighCycleRate();
       }
     } catch (RuntimeException e) {
       // should hopefully never occur