Foreign (Function) Memory API

Author: AnghelLeonard

Chapter07/JDK 22/P164_ArenaMappedMemorySegment/README.md

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+# Tackling mapped memory segments:
+Provide a brief introduction of mapped memory segments and exemplify them in Java code.
+
+## Using JDK 21

Chapter07/JDK 22/P164_ArenaMappedMemorySegment/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>java.modern.challenge</groupId>
+    <artifactId>P164_ArenaMappedMemorySegment</artifactId>
+    <version>1.0</version>
+    <packaging>jar</packaging>
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>22</maven.compiler.source>
+        <maven.compiler.target>22</maven.compiler.target>       
+    </properties>
+    <name>P164_ArenaMappedMemorySegment</name>    
+</project>

Chapter07/JDK 22/P164_ArenaMappedMemorySegment/readme1712836518222.txt

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+package modern.challenge;
+
+import java.io.IOException;
+import java.lang.foreign.Arena;
+import java.lang.foreign.MemorySegment;
+
+public class Main {
+
+    public static void main(String[] args) throws IOException {        
+
+        try (Arena arena = new MappedArena("readme")) {
+
+            MemorySegment segment1 = arena.allocate(100);
+            MemorySegment segment2 = arena.allocate(50);
+
+            segment1.setString(0, "Hello");
+            segment2.setString(0, "World");
+
+            System.out.println(segment1.getString(0) 
+                    + " " + segment2.getString(0));
+        }
+        
+        System.out.println("\n\nYou should find the files on disk in the project's root");
+    }
+}

Chapter07/JDK 22/P164_ArenaMappedMemorySegment/readme1712836518277.txt

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+package modern.challenge;
+
+import java.io.IOException;
+import java.lang.foreign.Arena;
+import java.lang.foreign.MemorySegment;
+import java.nio.channels.FileChannel;
+import static java.nio.channels.FileChannel.MapMode.READ_WRITE;
+import java.nio.file.Path;
+import static java.nio.file.StandardOpenOption.CREATE_NEW;
+import static java.nio.file.StandardOpenOption.READ;
+import static java.nio.file.StandardOpenOption.SPARSE;
+import static java.nio.file.StandardOpenOption.WRITE;
+
+public class MappedArena implements Arena {
+
+    private final String fileName;
+    private final Arena shared;
+
+    public MappedArena(String fileName) {
+
+        if (fileName == null) {
+            throw new IllegalArgumentException("The file name cannot be null");
+        }
+
+        this.fileName = fileName;
+        this.shared = Arena.ofShared();
+    }
+
+    @Override
+    public MemorySegment allocate(long byteSize, long byteAlignment) {
+
+        try (FileChannel file = FileChannel.open(
+                Path.of(fileName + System.currentTimeMillis() + ".txt"),
+                CREATE_NEW, SPARSE, READ, WRITE)) {
+
+            return file.map(READ_WRITE, 0, byteSize, shared);
+            
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    @Override
+    public MemorySegment.Scope scope() {
+        return shared.scope();
+    }
+
+    @Override
+    public void close() {
+        shared.close();
+    }  
+}