4.x: Concurrency limits module, and support in Helidon WebServer

all/pom.xml

@@ -463,6 +463,10 @@
             <groupId>io.helidon.common.features</groupId>
             <artifactId>helidon-common-features</artifactId>
         </dependency>
+        <dependency>
+            <groupId>io.helidon.common.concurrency</groupId>
+            <artifactId>helidon-common-concurrency-limits</artifactId>
+        </dependency>
         <dependency>
             <groupId>io.helidon.dbclient</groupId>
             <artifactId>helidon-dbclient</artifactId>
@@ -996,6 +1000,10 @@
             <groupId>io.helidon.webserver</groupId>
             <artifactId>helidon-webserver-service-common</artifactId>
         </dependency>
+        <dependency>
+            <groupId>io.helidon.webserver</groupId>
+            <artifactId>helidon-webserver-concurrency-limits</artifactId>
+        </dependency>
         <dependency>
             <groupId>io.helidon.webserver.testing.junit5</groupId>
             <artifactId>helidon-webserver-testing-junit5</artifactId>

bom/pom.xml

@@ -610,6 +610,11 @@
                 <artifactId>helidon-common-features</artifactId>
                 <version>${helidon.version}</version>
             </dependency>
+            <dependency>
+                <groupId>io.helidon.common.concurrency</groupId>
+                <artifactId>helidon-common-concurrency-limits</artifactId>
+                <version>${helidon.version}</version>
+            </dependency>
 
             <!-- db client -->
             <dependency>
@@ -1303,6 +1308,11 @@
                 <artifactId>helidon-webserver-service-common</artifactId>
                 <version>${helidon.version}</version>
             </dependency>
+            <dependency>
+                <groupId>io.helidon.webserver</groupId>
+                <artifactId>helidon-webserver-concurrency-limits</artifactId>
+                <version>${helidon.version}</version>
+            </dependency>
             <dependency>
                 <groupId>io.helidon.webserver.testing.junit5</groupId>
                 <artifactId>helidon-webserver-testing-junit5</artifactId>

common/concurrency/limits/README.md

@@ -0,0 +1,14 @@
+Concurrency Limits
+-----
+
+This module provides concurrency limits, so we can limit the number of concurrent, in-progress operations (for example in WebServer).
+
+The implemented concurrency limits are:
+
+| Key         | Weight | Description                                                                                                          |
+|-------------|--------|----------------------------------------------------------------------------------------------------------------------|
+| `semaphore` | `90`   | Semaphore based concurrency limit (highest weight, so the default), if max set to `0`, we have unlimited concurrency |
+| `aimd`      | `80`   | AIMD based limit (additive-increase/multiplicative-decrease)                                                         |
+| `bulkhead`  | `70`   | Uses a bulkhead with a queue, implementation provided by `helidon-fault-tolerance`                                   |
+
+Current usage: `helidon-webserver`

common/concurrency/limits/pom.xml

@@ -0,0 +1,117 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    Copyright (c) 2024 Oracle and/or its affiliates.
+
+    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
+
+        http://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.
+
+-->
+
+<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0"
+        xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>io.helidon.common.concurrency</groupId>
+        <artifactId>helidon-common-concurrency-project</artifactId>
+        <version>4.2.0-SNAPSHOT</version>
+        <relativePath>../pom.xml</relativePath>
+    </parent>
+
+    <artifactId>helidon-common-concurrency-limits</artifactId>
+    <name>Helidon Common Concurrency Limits</name>
+
+    <dependencies>
+        <dependency>
+            <groupId>io.helidon.common</groupId>
+            <artifactId>helidon-common</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>io.helidon.builder</groupId>
+            <artifactId>helidon-builder-api</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>io.helidon.common</groupId>
+            <artifactId>helidon-common-config</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>io.helidon.service</groupId>
+            <artifactId>helidon-service-registry</artifactId>
+            <optional>true</optional>
+        </dependency>
+        <dependency>
+            <groupId>org.hamcrest</groupId>
+            <artifactId>hamcrest-all</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <annotationProcessorPaths>
+                        <path>
+                            <groupId>io.helidon.codegen</groupId>
+                            <artifactId>helidon-codegen-apt</artifactId>
+                            <version>${helidon.version}</version>
+                        </path>
+                        <path>
+                            <groupId>io.helidon.builder</groupId>
+                            <artifactId>helidon-builder-codegen</artifactId>
+                            <version>${helidon.version}</version>
+                        </path>
+                        <path>
+                            <groupId>io.helidon.config.metadata</groupId>
+                            <artifactId>helidon-config-metadata-codegen</artifactId>
+                            <version>${helidon.version}</version>
+                        </path>
+                        <path>
+                            <groupId>io.helidon.codegen</groupId>
+                            <artifactId>helidon-codegen-helidon-copyright</artifactId>
+                            <version>${helidon.version}</version>
+                        </path>
+                    </annotationProcessorPaths>
+                </configuration>
+                <dependencies>
+                    <dependency>
+                        <groupId>io.helidon.codegen</groupId>
+                        <artifactId>helidon-codegen-apt</artifactId>
+                        <version>${helidon.version}</version>
+                    </dependency>
+                    <dependency>
+                        <groupId>io.helidon.builder</groupId>
+                        <artifactId>helidon-builder-codegen</artifactId>
+                        <version>${helidon.version}</version>
+                    </dependency>
+                    <dependency>
+                        <groupId>io.helidon.config.metadata</groupId>
+                        <artifactId>helidon-config-metadata-codegen</artifactId>
+                        <version>${helidon.version}</version>
+                    </dependency>
+                    <dependency>
+                        <groupId>io.helidon.codegen</groupId>
+                        <artifactId>helidon-codegen-helidon-copyright</artifactId>
+                        <version>${helidon.version}</version>
+                    </dependency>
+                </dependencies>
+            </plugin>
+        </plugins>
+    </build>
+</project>

common/concurrency/limits/src/main/java/io/helidon/common/concurrency/limits/AimdLimit.java

@@ -0,0 +1,129 @@
+/*
+ * Copyright (c) 2024 Oracle and/or its affiliates.
+ *
+ * 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
+ *
+ *     http://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 io.helidon.common.concurrency.limits;
+
+import java.util.concurrent.Callable;
+import java.util.concurrent.Semaphore;
+import java.util.function.Consumer;
+
+import io.helidon.builder.api.RuntimeType;
+import io.helidon.common.config.Config;
+
+/**
+ * AIMD based limiter.
+ * <p>
+ * The additive-increase/multiplicative-decrease (AIMD) algorithm is a feedback control algorithm best known for its use in TCP
+ * congestion control. AIMD combines linear growth of the congestion window when there is no congestion with an exponential
+ * reduction when congestion is detected.
+ */
+@SuppressWarnings("removal")
+@RuntimeType.PrototypedBy(AimdLimitConfig.class)
+public class AimdLimit implements Limit, SemaphoreLimit, RuntimeType.Api<AimdLimitConfig> {
+    static final String TYPE = "aimd";
+
+    private final AimdLimitConfig config;
+    private final AimdLimitImpl aimdLimitImpl;
+
+    private AimdLimit(AimdLimitConfig config) {
+        this.config = config;
+        this.aimdLimitImpl = new AimdLimitImpl(config);
+    }
+
+    /**
+     * Create a new fluent API builder to construct {@link io.helidon.common.concurrency.limits.AimdLimit}
+     * instance.
+     *
+     * @return fluent API builder
+     */
+    public static AimdLimitConfig.Builder builder() {
+        return AimdLimitConfig.builder();
+    }
+
+    /**
+     * Create a new instance with all defaults.
+     *
+     * @return a new limit instance
+     */
+    public static AimdLimit create() {
+        return builder().build();
+    }
+
+    /**
+     * Create a new instance from configuration.
+     *
+     * @param config configuration of the AIMD limit
+     * @return a new limit instance configured from {@code config}
+     */
+    public static AimdLimit create(Config config) {
+        return builder()
+                .config(config)
+                .build();
+    }
+
+    /**
+     * Create a new instance from configuration.
+     *
+     * @param config configuration of the AIMD limit
+     * @return a new limit instance configured from {@code config}
+     */
+    public static AimdLimit create(AimdLimitConfig config) {
+        return new AimdLimit(config);
+    }
+
+    /**
+     * Create a new instance customizing its configuration.
+     *
+     * @param consumer consumer of configuration builder
+     * @return a new limit instance configured from the builder
+     */
+    public static AimdLimit create(Consumer<AimdLimitConfig.Builder> consumer) {
+        return builder()
+                .update(consumer)
+                .build();
+    }
+
+    @Override
+    public <T> T invoke(Callable<T> callable) throws Exception {
+        return aimdLimitImpl.invoke(callable);
+    }
+
+    @Override
+    public void invoke(Runnable runnable) throws Exception {
+        aimdLimitImpl.invoke(runnable);
+    }
+
+    @SuppressWarnings("removal")
+    @Override
+    public Semaphore semaphore() {
+        return aimdLimitImpl.semaphore();
+    }
+
+    @Override
+    public String name() {
+        return config.name();
+    }
+
+    @Override
+    public String type() {
+        return TYPE;
+    }
+
+    @Override
+    public AimdLimitConfig prototype() {
+        return config;
+    }
+}