SimpleAsyncTaskScheduler runs fixed-delay tasks on scheduler thread

Closes gh-31334

Author: jhoeller

spring-context/src/main/java/org/springframework/scheduling/concurrent/SimpleAsyncTaskScheduler.java

@@ -46,6 +46,11 @@
  * separate thread. This is an attractive choice with virtual threads on JDK 21,
  * expecting common usage with {@link #setVirtualThreads setVirtualThreads(true)}.
  *
+ * <p><b>NOTE: Scheduling with a fixed delay enforces execution on the single
+ * scheduler thread, in order to provide traditional fixed-delay semantics!</b>
+ * Prefer the use of fixed rates or cron triggers instead which are a better fit
+ * with this thread-per-task scheduler variant.
+ *
  * <p>Supports a graceful shutdown through {@link #setTaskTerminationTimeout},
  * at the expense of task tracking overhead per execution thread at runtime.
  * Supports limiting concurrent threads through {@link #setConcurrencyLimit}.
@@ -234,7 +239,8 @@ public ScheduledFuture<?> scheduleAtFixedRate(Runnable task, Duration period) {
 	public ScheduledFuture<?> scheduleWithFixedDelay(Runnable task, Instant startTime, Duration delay) {
 		Duration initialDelay = Duration.between(this.clock.instant(), startTime);
 		try {
-			return this.scheduledExecutor.scheduleWithFixedDelay(scheduledTask(task),
+			// Blocking task on scheduler thread for fixed delay semantics
+			return this.scheduledExecutor.scheduleWithFixedDelay(task,
 					NANO.convert(initialDelay), NANO.convert(delay), NANO);
 		}
 		catch (RejectedExecutionException ex) {
@@ -245,7 +251,8 @@ public ScheduledFuture<?> scheduleWithFixedDelay(Runnable task, Instant startTim
 	@Override
 	public ScheduledFuture<?> scheduleWithFixedDelay(Runnable task, Duration delay) {
 		try {
-			return this.scheduledExecutor.scheduleWithFixedDelay(scheduledTask(task),
+			// Blocking task on scheduler thread for fixed delay semantics
+			return this.scheduledExecutor.scheduleWithFixedDelay(task,
 					0, NANO.convert(delay), NANO);
 		}
 		catch (RejectedExecutionException ex) {

spring-context/src/test/java/org/springframework/scheduling/annotation/EnableSchedulingTests.java

@@ -175,7 +175,20 @@ public void withQualifiedSchedulerAndPlaceholder() throws InterruptedException {
 
 		Thread.sleep(110);
 		assertThat(ctx.getBean(AtomicInteger.class).get()).isGreaterThanOrEqualTo(10);
-		assertThat(ctx.getBean(QualifiedExplicitSchedulerConfigWithPlaceholder.class).threadName).startsWith("explicitScheduler1");
+		assertThat(ctx.getBean(QualifiedExplicitSchedulerConfigWithPlaceholder.class).threadName)
+				.startsWith("explicitScheduler1").isNotEqualTo("explicitScheduler1-1");
+	}
+
+	@Test
+	@EnabledForTestGroups(LONG_RUNNING)
+	public void withQualifiedSchedulerWithFixedDelayTask() throws InterruptedException {
+		ctx = new AnnotationConfigApplicationContext(QualifiedExplicitSchedulerConfigWithFixedDelayTask.class);
+		assertThat(ctx.getBean(ScheduledTaskHolder.class).getScheduledTasks()).hasSize(1);
+
+		Thread.sleep(110);
+		assertThat(ctx.getBean(AtomicInteger.class).get()).isBetween(4, 5);
+		assertThat(ctx.getBean(QualifiedExplicitSchedulerConfigWithFixedDelayTask.class).threadName)
+				.isEqualTo("explicitScheduler1-1");
 	}
 
 	@Test
@@ -228,7 +241,20 @@ public void withInitiallyDelayedFixedRateTask() throws InterruptedException {
 
 		// The @Scheduled method should have been called several times
 		// but not more times than the delay allows.
-		assertThat(counter.get()).isBetween(2, 10);
+		assertThat(counter.get()).isBetween(6, 10);
+	}
+
+	@Test
+	@EnabledForTestGroups(LONG_RUNNING)
+	public void withInitiallyDelayedFixedDelayTask() throws InterruptedException {
+		ctx = new AnnotationConfigApplicationContext(FixedDelayTaskConfig_withInitialDelay.class);
+
+		Thread.sleep(1950);
+		AtomicInteger counter = ctx.getBean(AtomicInteger.class);
+
+		// The @Scheduled method should have been called several times
+		// but not more times than the delay allows.
+		assertThat(counter.get()).isBetween(1, 5);
 	}
 
 	@Test
@@ -333,14 +359,14 @@ static class AmbiguousExplicitSchedulerConfig {
 		@Bean
 		public TaskScheduler taskScheduler1() {
 			SimpleAsyncTaskScheduler scheduler = new SimpleAsyncTaskScheduler();
-			scheduler.setThreadNamePrefix("explicitScheduler1");
+			scheduler.setThreadNamePrefix("explicitScheduler1-");
 			return scheduler;
 		}
 
 		@Bean
 		public TaskScheduler taskScheduler2() {
 			ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();
-			scheduler.setThreadNamePrefix("explicitScheduler2");
+			scheduler.setThreadNamePrefix("explicitScheduler2-");
 			return scheduler;
 		}
 
@@ -359,14 +385,14 @@ static class ExplicitScheduledTaskRegistrarConfig implements SchedulingConfigure
 		@Bean
 		public TaskScheduler taskScheduler1() {
 			SimpleAsyncTaskScheduler scheduler = new SimpleAsyncTaskScheduler();
-			scheduler.setThreadNamePrefix("explicitScheduler1");
+			scheduler.setThreadNamePrefix("explicitScheduler1-");
 			return scheduler;
 		}
 
 		@Bean
 		public TaskScheduler taskScheduler2() {
 			ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();
-			scheduler.setThreadNamePrefix("explicitScheduler2");
+			scheduler.setThreadNamePrefix("explicitScheduler2-");
 			return scheduler;
 		}
 
@@ -397,14 +423,14 @@ static class QualifiedExplicitSchedulerConfig {
 		@Bean @Qualifier("myScheduler")
 		public TaskScheduler taskScheduler1() {
 			SimpleAsyncTaskScheduler scheduler = new SimpleAsyncTaskScheduler();
-			scheduler.setThreadNamePrefix("explicitScheduler1");
+			scheduler.setThreadNamePrefix("explicitScheduler1-");
 			return scheduler;
 		}
 
 		@Bean
 		public TaskScheduler taskScheduler2() {
 			ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();
-			scheduler.setThreadNamePrefix("explicitScheduler2");
+			scheduler.setThreadNamePrefix("explicitScheduler2-");
 			return scheduler;
 		}
 
@@ -414,9 +440,10 @@ public AtomicInteger counter() {
 		}
 
 		@Scheduled(fixedRate = 10, scheduler = "myScheduler")
-		public void task() {
+		public void task() throws InterruptedException {
 			threadName = Thread.currentThread().getName();
 			counter().incrementAndGet();
+			Thread.sleep(10);
 		}
 	}
 
@@ -430,14 +457,14 @@ static class QualifiedExplicitSchedulerConfigWithPlaceholder {
 		@Bean @Qualifier("myScheduler")
 		public TaskScheduler taskScheduler1() {
 			SimpleAsyncTaskScheduler scheduler = new SimpleAsyncTaskScheduler();
-			scheduler.setThreadNamePrefix("explicitScheduler1");
+			scheduler.setThreadNamePrefix("explicitScheduler1-");
 			return scheduler;
 		}
 
 		@Bean
 		public TaskScheduler taskScheduler2() {
 			ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();
-			scheduler.setThreadNamePrefix("explicitScheduler2");
+			scheduler.setThreadNamePrefix("explicitScheduler2-");
 			return scheduler;
 		}
 
@@ -447,9 +474,10 @@ public AtomicInteger counter() {
 		}
 
 		@Scheduled(fixedRate = 10, scheduler = "${scheduler}")
-		public void task() {
+		public void task() throws InterruptedException {
 			threadName = Thread.currentThread().getName();
 			counter().incrementAndGet();
+			Thread.sleep(10);
 		}
 
 		@Bean
@@ -463,21 +491,55 @@ public static PropertySourcesPlaceholderConfigurer placeholderConfigurer() {
 	}
 
 
+	@Configuration
+	@EnableScheduling
+	static class QualifiedExplicitSchedulerConfigWithFixedDelayTask {
+
+		String threadName;
+
+		@Bean @Qualifier("myScheduler")
+		public TaskScheduler taskScheduler1() {
+			SimpleAsyncTaskScheduler scheduler = new SimpleAsyncTaskScheduler();
+			scheduler.setThreadNamePrefix("explicitScheduler1-");
+			return scheduler;
+		}
+
+		@Bean
+		public TaskScheduler taskScheduler2() {
+			ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();
+			scheduler.setThreadNamePrefix("explicitScheduler2-");
+			return scheduler;
+		}
+
+		@Bean
+		public AtomicInteger counter() {
+			return new AtomicInteger();
+		}
+
+		@Scheduled(fixedDelay = 10, scheduler = "myScheduler")
+		public void task() throws InterruptedException {
+			threadName = Thread.currentThread().getName();
+			counter().incrementAndGet();
+			Thread.sleep(10);
+		}
+	}
+
+
 	@Configuration
 	@EnableScheduling
 	static class SchedulingEnabled_withAmbiguousTaskSchedulers_butNoActualTasks {
 
 		@Bean
 		public TaskScheduler taskScheduler1() {
 			SimpleAsyncTaskScheduler scheduler = new SimpleAsyncTaskScheduler();
-			scheduler.setThreadNamePrefix("explicitScheduler1");
+			scheduler.setThreadNamePrefix("explicitScheduler1-");
 			return scheduler;
 		}
 
 		@Bean
 		public TaskScheduler taskScheduler2() {
 			ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();
-			scheduler.setThreadNamePrefix("explicitScheduler2");
+			scheduler.setThreadNamePrefix("explicitScheduler2-");
 			return scheduler;
 		}
 	}
@@ -494,15 +556,15 @@ public void task() {
 		@Bean
 		public TaskScheduler taskScheduler1() {
 			SimpleAsyncTaskScheduler scheduler = new SimpleAsyncTaskScheduler();
-			scheduler.setThreadNamePrefix("explicitScheduler1");
+			scheduler.setThreadNamePrefix("explicitScheduler1-");
 			scheduler.setConcurrencyLimit(1);
 			return scheduler;
 		}
 
 		@Bean
 		public TaskScheduler taskScheduler2() {
 			ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();
-			scheduler.setThreadNamePrefix("explicitScheduler2");
+			scheduler.setThreadNamePrefix("explicitScheduler2-");
 			return scheduler;
 		}
 	}
@@ -620,8 +682,26 @@ public AtomicInteger counter() {
 		}
 
 		@Scheduled(initialDelay = 1000, fixedRate = 100)
-		public void task() {
+		public void task() throws InterruptedException {
+			counter().incrementAndGet();
+			Thread.sleep(100);
+		}
+	}
+
+
+	@Configuration
+	@EnableScheduling
+	static class FixedDelayTaskConfig_withInitialDelay {
+
+		@Bean
+		public AtomicInteger counter() {
+			return new AtomicInteger();
+		}
+
+		@Scheduled(initialDelay = 1000, fixedDelay = 100)
+		public void task() throws InterruptedException {
 			counter().incrementAndGet();
+			Thread.sleep(100);
 		}
 	}