Provide programmatic alternative to @ConcurrencyLimit

Closes gh-35460

Signed-off-by: Geonhu Park <parkgeonhu@gmail.com>

spring-core/src/main/java/org/springframework/core/concurrency/ConcurrencyLimitTemplate.java

@@ -0,0 +1,72 @@
+/*
+ * Copyright 2002-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.core.concurrency;
+
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.util.ConcurrencyThrottleSupport;
+
+/**
+ * Template-style API that throttles concurrent executions of user-provided callbacks
+ * according to a configurable concurrency limit.
+ *
+ * <p>Blocking semantics are identical to {@link ConcurrencyThrottleSupport}:
+ * when the configured limit is reached, additional callers will block until a
+ * permit becomes available.
+ *
+ * <p>The default concurrency limit of this template is 1.
+ *
+ * @author Geonhu Park
+ * @since 7.1
+ * @see ConcurrencyThrottleSupport
+ */
+@SuppressWarnings("serial")
+public class ConcurrencyLimitTemplate extends ConcurrencyThrottleSupport {
+
+	/**
+	 * Create a default {@code ConcurrencyLimitTemplate}
+	 * with concurrency limit 1.
+	 */
+	public ConcurrencyLimitTemplate() {
+		this(1);
+	}
+
+	/**
+	 * Create a {@code ConcurrencyThrottleInterceptor}
+	 * with the given concurrency limit.
+	 */
+	public ConcurrencyLimitTemplate(int concurrencyLimit) {
+		setConcurrencyLimit(concurrencyLimit);
+	}
+
+	/**
+	 * Execute the supplied callback under the configured concurrency limit.
+	 * @param concurrencyLimited the unit of work to run
+	 * @param <R> the result type (nullable)
+	 * @return the callback's result (possibly {@code null})
+	 * @throws Throwable any exception thrown by the callback
+	 */
+	public <R extends @Nullable Object> @Nullable R execute(ConcurrencyLimited<R> concurrencyLimited) throws Throwable {
+		beforeAccess();
+		try {
+			return concurrencyLimited.execute();
+		}
+		finally {
+			afterAccess();
+		}
+	}
+}

spring-core/src/main/java/org/springframework/core/concurrency/ConcurrencyLimited.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2002-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.core.concurrency;
+
+import org.jspecify.annotations.Nullable;
+
+/**
+ * Functional callback representing a single unit of work to be executed under
+ * the concurrency throttling of a {@link ConcurrencyLimitTemplate}.
+ *
+ * @author Geonhu Park
+ * @since 7.1
+ * @param <R> the result type (nullable)
+ * @see ConcurrencyLimitTemplate
+ */
+@FunctionalInterface
+public interface ConcurrencyLimited<R extends @Nullable Object> {
+
+	/**
+	 * Execute the concurrency-limited operation.
+	 * @return the result (may be {@code null})
+	 * @throws Throwable any error from the underlying operation
+	 */
+	R execute() throws Throwable;
+}

spring-core/src/main/java/org/springframework/core/concurrency/package-info.java

@@ -0,0 +1,5 @@
+/**
+ * Concurrency limiting (throttling) support via {@link org.springframework.core.concurrency.ConcurrencyLimitTemplate}
+ * and {@link org.springframework.core.concurrency.ConcurrencyLimited}.
+ */
+package org.springframework.core.concurrency;

spring-core/src/main/java/org/springframework/util/ConcurrencyThrottleSupport.java

@@ -44,6 +44,7 @@ import org.apache.commons.logging.LogFactory;
  * @see #beforeAccess()
  * @see #afterAccess()
  * @see org.springframework.aop.interceptor.ConcurrencyThrottleInterceptor
+ * @see org.springframework.core.concurrency.ConcurrencyLimitTemplate
  * @see java.io.Serializable
  */
 @SuppressWarnings("serial")

spring-core/src/test/java/org/springframework/core/concurrency/ConcurrencyLimitTemplateTests.java

@@ -0,0 +1,111 @@
+/*
+ * Copyright 2002-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.core.concurrency;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+/**
+ * Tests for {@link ConcurrencyLimitTemplate}.
+ *
+ * @author Geonhu Park
+ */
+class ConcurrencyLimitTemplateTests {
+
+	private static final Log logger = LogFactory.getLog(ConcurrencyLimitTemplateTests.class);
+
+	private static final int NR_OF_THREADS = 100;
+
+	private static final int NR_OF_ITERATIONS = 1000;
+
+	@ParameterizedTest
+	@ValueSource(ints = {1, 10})
+	void multipleThreadsWithLimit(int concurrencyLimit) {
+		ConcurrencyLimitTemplate template = new ConcurrencyLimitTemplate(concurrencyLimit);
+
+		Thread[] threads = new Thread[NR_OF_THREADS];
+		for (int i = 0; i < NR_OF_THREADS; i++) {
+			threads[i] = new ConcurrencyThread(template, null);
+			threads[i].start();
+		}
+		for (int i = 0; i < NR_OF_THREADS / 10; i++) {
+			try {
+				Thread.sleep(5);
+			}
+			catch (InterruptedException ex) {
+				ex.printStackTrace();
+			}
+			threads[i] = new ConcurrencyThread(template,
+					(i % 2 == 0 ? new OutOfMemoryError() : new IllegalStateException()));
+			threads[i].start();
+		}
+		for (Thread t : threads) {
+			try {
+				t.join();
+			}
+			catch (InterruptedException ex) {
+				ex.printStackTrace();
+			}
+		}
+	}
+
+	private static class ConcurrencyThread extends Thread {
+
+		private final ConcurrencyLimitTemplate template;
+		private final Throwable ex;
+
+		ConcurrencyThread(ConcurrencyLimitTemplate template, Throwable ex) {
+			this.template = template;
+			this.ex = ex;
+		}
+
+		@Override
+		public void run() {
+			if (this.ex != null) {
+				try {
+					this.template.execute(() -> {
+						throw this.ex;
+					});
+				}
+				catch (RuntimeException | Error err) {
+					if (err == this.ex) {
+						logger.info("Expected exception thrown", err);
+					}
+					else {
+						ex.printStackTrace();
+					}
+				}
+				catch (Throwable th) {
+					th.printStackTrace();
+				}
+			}
+			else {
+				for (int i = 0; i < NR_OF_ITERATIONS; i++) {
+					try {
+						this.template.execute(() -> null);
+					}
+					catch (Throwable th) {
+						th.printStackTrace();
+						break;
+					}
+				}
+			}
+		}
+	}
+}