StreamSelectLoop was treating seconds as microseconds, outward behavior was correct but internally many short sleeps/select calls were being made.

Author: jmalloc

src/React/EventLoop/StreamSelectLoop.php

@@ -13,6 +13,8 @@
  */
 class StreamSelectLoop implements LoopInterface
 {
+    const MICROSECONDS_PER_SECOND = 1000000;
+
     private $nextTickQueue;
     private $futureTickQueue;
     private $timers;
@@ -193,7 +195,7 @@ public function run()
                 break;
             }
 
-            $this->waitForStreamActivity($timeout);
+            $this->waitForStreamActivity($timeout * self::MICROSECONDS_PER_SECOND);
         }
     }