Separate internal ScheduledExecutorService for fixed-delay tasks

Closes gh-33408

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

@@ -52,7 +52,7 @@ import org.springframework.util.concurrent.ListenableFuture;
  * 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
+ * <p><b>NOTE: Scheduling with a fixed delay enforces execution on a 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.
@@ -113,9 +113,13 @@ public class SimpleAsyncTaskScheduler extends SimpleAsyncTaskExecutor implements
 	private static final TimeUnit NANO = TimeUnit.NANOSECONDS;
 
 
-	private final ScheduledExecutorService scheduledExecutor = createScheduledExecutor();
+	private final ScheduledExecutorService triggerExecutor = createScheduledExecutor();
 
-	private final ExecutorLifecycleDelegate lifecycleDelegate = new ExecutorLifecycleDelegate(this.scheduledExecutor);
+	private final ExecutorLifecycleDelegate triggerLifecycle = new ExecutorLifecycleDelegate(this.triggerExecutor);
+
+	private final ScheduledExecutorService fixedDelayExecutor = createFixedDelayExecutor();
+
+	private final ExecutorLifecycleDelegate fixedDelayLifecycle = new ExecutorLifecycleDelegate(this.fixedDelayExecutor);
 
 	@Nullable
 	private ErrorHandler errorHandler;
@@ -195,11 +199,24 @@ public class SimpleAsyncTaskScheduler extends SimpleAsyncTaskExecutor implements
 		return new ScheduledThreadPoolExecutor(1, this::newThread) {
 			@Override
 			protected void beforeExecute(Thread thread, Runnable task) {
-				lifecycleDelegate.beforeExecute(thread);
+				triggerLifecycle.beforeExecute(thread);
 			}
 			@Override
 			protected void afterExecute(Runnable task, Throwable ex) {
-				lifecycleDelegate.afterExecute();
+				triggerLifecycle.afterExecute();
+			}
+		};
+	}
+
+	private ScheduledExecutorService createFixedDelayExecutor() {
+		return new ScheduledThreadPoolExecutor(1, this::newThread) {
+			@Override
+			protected void beforeExecute(Thread thread, Runnable task) {
+				fixedDelayLifecycle.beforeExecute(thread);
+			}
+			@Override
+			protected void afterExecute(Runnable task, Throwable ex) {
+				fixedDelayLifecycle.afterExecute();
 			}
 		};
 	}
@@ -227,7 +244,7 @@ public class SimpleAsyncTaskScheduler extends SimpleAsyncTaskExecutor implements
 		if (this.errorHandler != null) {
 			this.errorHandler.handleError(ex);
 		}
-		else if (this.scheduledExecutor.isShutdown()) {
+		else if (this.triggerExecutor.isShutdown()) {
 			LogFactory.getLog(getClass()).debug("Ignoring scheduled task exception after shutdown", ex);
 		}
 		else {
@@ -271,10 +288,10 @@ public class SimpleAsyncTaskScheduler extends SimpleAsyncTaskExecutor implements
 			ErrorHandler errorHandler =
 					(this.errorHandler != null ? this.errorHandler : TaskUtils.getDefaultErrorHandler(true));
 			return new ReschedulingRunnable(
-					delegate, trigger, this.clock, this.scheduledExecutor, errorHandler).schedule();
+					delegate, trigger, this.clock, this.triggerExecutor, errorHandler).schedule();
 		}
 		catch (RejectedExecutionException ex) {
-			throw new TaskRejectedException(this.scheduledExecutor, task, ex);
+			throw new TaskRejectedException(this.triggerExecutor, task, ex);
 		}
 	}
 
@@ -282,10 +299,10 @@ public class SimpleAsyncTaskScheduler extends SimpleAsyncTaskExecutor implements
 	public ScheduledFuture<?> schedule(Runnable task, Instant startTime) {
 		Duration delay = Duration.between(this.clock.instant(), startTime);
 		try {
-			return this.scheduledExecutor.schedule(scheduledTask(task), NANO.convert(delay), NANO);
+			return this.triggerExecutor.schedule(scheduledTask(task), NANO.convert(delay), NANO);
 		}
 		catch (RejectedExecutionException ex) {
-			throw new TaskRejectedException(this.scheduledExecutor, task, ex);
+			throw new TaskRejectedException(this.triggerExecutor, task, ex);
 		}
 	}
 
@@ -293,22 +310,22 @@ public class SimpleAsyncTaskScheduler extends SimpleAsyncTaskExecutor implements
 	public ScheduledFuture<?> scheduleAtFixedRate(Runnable task, Instant startTime, Duration period) {
 		Duration initialDelay = Duration.between(this.clock.instant(), startTime);
 		try {
-			return this.scheduledExecutor.scheduleAtFixedRate(scheduledTask(task),
+			return this.triggerExecutor.scheduleAtFixedRate(scheduledTask(task),
 					NANO.convert(initialDelay), NANO.convert(period), NANO);
 		}
 		catch (RejectedExecutionException ex) {
-			throw new TaskRejectedException(this.scheduledExecutor, task, ex);
+			throw new TaskRejectedException(this.triggerExecutor, task, ex);
 		}
 	}
 
 	@Override
 	public ScheduledFuture<?> scheduleAtFixedRate(Runnable task, Duration period) {
 		try {
-			return this.scheduledExecutor.scheduleAtFixedRate(scheduledTask(task),
+			return this.triggerExecutor.scheduleAtFixedRate(scheduledTask(task),
 					0, NANO.convert(period), NANO);
 		}
 		catch (RejectedExecutionException ex) {
-			throw new TaskRejectedException(this.scheduledExecutor, task, ex);
+			throw new TaskRejectedException(this.triggerExecutor, task, ex);
 		}
 	}
 
@@ -317,11 +334,11 @@ public class SimpleAsyncTaskScheduler extends SimpleAsyncTaskExecutor implements
 		Duration initialDelay = Duration.between(this.clock.instant(), startTime);
 		try {
 			// Blocking task on scheduler thread for fixed delay semantics
-			return this.scheduledExecutor.scheduleWithFixedDelay(taskOnSchedulerThread(task),
+			return this.fixedDelayExecutor.scheduleWithFixedDelay(taskOnSchedulerThread(task),
 					NANO.convert(initialDelay), NANO.convert(delay), NANO);
 		}
 		catch (RejectedExecutionException ex) {
-			throw new TaskRejectedException(this.scheduledExecutor, task, ex);
+			throw new TaskRejectedException(this.fixedDelayExecutor, task, ex);
 		}
 	}
 
@@ -329,45 +346,54 @@ public class SimpleAsyncTaskScheduler extends SimpleAsyncTaskExecutor implements
 	public ScheduledFuture<?> scheduleWithFixedDelay(Runnable task, Duration delay) {
 		try {
 			// Blocking task on scheduler thread for fixed delay semantics
-			return this.scheduledExecutor.scheduleWithFixedDelay(taskOnSchedulerThread(task),
+			return this.fixedDelayExecutor.scheduleWithFixedDelay(taskOnSchedulerThread(task),
 					0, NANO.convert(delay), NANO);
 		}
 		catch (RejectedExecutionException ex) {
-			throw new TaskRejectedException(this.scheduledExecutor, task, ex);
+			throw new TaskRejectedException(this.fixedDelayExecutor, task, ex);
 		}
 	}
 
 
 	@Override
 	public void start() {
-		this.lifecycleDelegate.start();
+		this.triggerLifecycle.start();
+		this.fixedDelayLifecycle.start();
 	}
 
 	@Override
 	public void stop() {
-		this.lifecycleDelegate.stop();
+		this.triggerLifecycle.stop();
+		this.fixedDelayLifecycle.stop();
 	}
 
 	@Override
 	public void stop(Runnable callback) {
-		this.lifecycleDelegate.stop(callback);
+		this.triggerLifecycle.stop();  // no callback necessary since it's just triggers with hand-offs
+		this.fixedDelayLifecycle.stop(callback);  // callback for currently executing fixed-delay tasks
 	}
 
 	@Override
 	public boolean isRunning() {
-		return this.lifecycleDelegate.isRunning();
+		return this.triggerLifecycle.isRunning();
 	}
 
 	@Override
 	public void onApplicationEvent(ContextClosedEvent event) {
 		if (event.getApplicationContext() == this.applicationContext) {
-			this.scheduledExecutor.shutdown();
+			this.triggerExecutor.shutdown();
+			this.fixedDelayExecutor.shutdown();
 		}
 	}
 
 	@Override
 	public void close() {
-		for (Runnable remainingTask : this.scheduledExecutor.shutdownNow()) {
+		for (Runnable remainingTask : this.triggerExecutor.shutdownNow()) {
+			if (remainingTask instanceof Future<?> future) {
+				future.cancel(true);
+			}
+		}
+		for (Runnable remainingTask : this.fixedDelayExecutor.shutdownNow()) {
 			if (remainingTask instanceof Future<?> future) {
 				future.cancel(true);
 			}