Scheduler: document @Scheduled#executionMaxDelay()

- also add test for JobDefinition#setExecutionMaxDelay()

docs/src/main/asciidoc/scheduler-reference.adoc

@@ -220,7 +220,8 @@ Property Expressions. (Note that `"{property.path}"` style expressions are still
 void myMethod() { }
 ----
 
-=== Delayed Execution
+[[delayed_start]]
+=== Delayed Start of a Trigger
 
 `@Scheduled` provides two ways to delay the time a trigger should start firing at.
 
@@ -249,9 +250,8 @@ void everyTwoSeconds() { }
 NOTE: If `@Scheduled#delay()` is set to a value greater than zero the value of `@Scheduled#delayed()` is ignored.
 
 The main advantage over `@Scheduled#delay()` is that the value is configurable.
-The `delay` attribute supports <<config-reference#property-expressions,Property Expressions>> including default values and nested
-Property Expressions. (Note that `"{property.path}"` style expressions are still supported but don't offer the full functionality of Property Expressions.)
-
+The `delay` attribute supports <<config-reference#property-expressions,Property Expressions>> including default values and nested Property Expressions.
+(Note that `"{property.path}"` style expressions are still supported but don't offer the full functionality of Property Expressions.)
 
 [source,java]
 ----
@@ -260,6 +260,26 @@ void everyTwoSeconds() { }
 ----
 <1> The config property `myMethod.delay.expr` is used to set the delay.
 
+[[delayed_execution]]
+=== Delayed Execution
+
+`@Scheduled#executionMaxDelay()` can be set to delay each execution of a scheduled method.
+The value represents the maximum delay between the activation of the trigger and the execution of the scheduled method.
+The actual delay varies randomly over time but it never exceeds the maximum value.
+
+The value is parsed with `DurationConverter#parseDuration(String)`.
+It can be a property expression.
+In that case, the scheduler attempts to use the configured value instead: `@Scheduled(executionMaxDelay = "${myJob.maxDelay}")`.
+Additionally, the property expression can specify a default value:
+`@Scheduled(executionMaxDelay = "${myJob.maxDelay}:500ms}")`.
+
+[source,java]
+----
+@Scheduled(every = "2s", executionMaxDelay = "500ms") <1>
+void everyTwoSeconds() { }
+----
+<1> The delay will be a value between 0 and 500 milliseconds. As a result, the period between to `everyTwoSeconds()` executions will be roughly between two and two and a half seconds.
+
 [[concurrent_execution]]
 === Concurrent Execution
 

extensions/scheduler/deployment/src/test/java/io/quarkus/scheduler/test/delayedexecution/DelayedExecutionTest.java

@@ -1,6 +1,5 @@
 package io.quarkus.scheduler.test.delayedexecution;
 
-import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.util.concurrent.CountDownLatch;
@@ -11,8 +10,10 @@
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.RegisterExtension;
 
+import io.quarkus.runtime.StartupEvent;
 import io.quarkus.scheduler.DelayedExecution;
 import io.quarkus.scheduler.Scheduled;
+import io.quarkus.scheduler.Scheduler;
 import io.quarkus.test.QuarkusUnitTest;
 
 public class DelayedExecutionTest {
@@ -24,23 +25,38 @@ public class DelayedExecutionTest {
     @Test
     public void testSimpleScheduledJobs() throws InterruptedException {
         assertTrue(Jobs.EVENT_LATCH.await(5, TimeUnit.SECONDS));
-        assertTrue(Jobs.LATCH.await(5, TimeUnit.SECONDS));
+        assertTrue(Jobs.LATCH1.await(5, TimeUnit.SECONDS));
+        assertTrue(Jobs.LATCH2.await(5, TimeUnit.SECONDS));
     }
 
     static class Jobs {
 
-        static final CountDownLatch LATCH = new CountDownLatch(1);
-        static final CountDownLatch EVENT_LATCH = new CountDownLatch(1);
+        static final CountDownLatch LATCH1 = new CountDownLatch(1);
+        static final CountDownLatch LATCH2 = new CountDownLatch(1);
+        static final CountDownLatch EVENT_LATCH = new CountDownLatch(2);
 
         @Scheduled(identity = "foo", every = "1s", executionMaxDelay = "500ms")
         static void everySecond() {
-            LATCH.countDown();
+            LATCH1.countDown();
+        }
+
+        void start(@Observes StartupEvent event, Scheduler scheduler) {
+            scheduler.newJob("bar")
+                    .setInterval("1s")
+                    .setExecutionMaxDelay("500ms")
+                    .setTask(se -> {
+                        LATCH2.countDown();
+                    }).schedule();
         }
 
         void onDelay(@Observes DelayedExecution delayedExecution) {
             assertTrue(delayedExecution.getDelay() < 500);
-            assertEquals("foo", delayedExecution.getExecution().getTrigger().getId());
-            EVENT_LATCH.countDown();
+            String id = delayedExecution.getExecution().getTrigger().getId();
+            if ("foo".equals(id) || "bar".equals(id)) {
+                EVENT_LATCH.countDown();
+            } else {
+                throw new IllegalStateException("Invalid job identity: " + id);
+            }
         }
 
     }