Foreign (Function) Memory API

Author: AnghelLeonard

Chapter07/JDK 22/P164_MappedMemorySegment/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_MappedMemorySegment/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_MappedMemorySegment</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_MappedMemorySegment</name>    
+</project>

Chapter07/JDK 22/P164_MappedMemorySegment/readme.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;
+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 Main {
+
+    public static void main(String[] args) throws IOException {
+        
+        try (FileChannel file = FileChannel.open(
+                Path.of("readme.txt"), CREATE, READ, WRITE);                 
+                Arena arena = Arena.ofConfined()) {
+
+            MemorySegment segment
+                    = file.map(READ_WRITE, 0, 1048576, arena);  // 1 Megabyte = 1048576 bytes
+                                                                // 1 Gigabyte = 1073741824 bytes
+
+            // write the data                                                                        
+            segment.setString(0, "This is a readme file ...");
+            segment.setString(1048576/2, "Here is the middle of the file ...");
+            segment.setString(1048576-32, "Here is the end of the file ...");
+            
+            // read some data
+            System.out.println(segment.getString(1048576/2));
+        }
+        
+        try (FileChannel file = FileChannel.open(
+                Path.of("sparse_readme.txt"), CREATE_NEW, SPARSE, READ, WRITE);                 
+                Arena arena = Arena.ofConfined()) {
+
+            MemorySegment segment
+                    = file.map(READ_WRITE, 0, 1048576, arena);  // 1 Megabyte = 1048576 bytes
+                                                                // 1 Gigabyte = 1073741824 bytes
+
+            // write the data                                                                        
+            segment.setString(0, "This is a readme file ...");
+            segment.setString(1048576/2, "Here is the middle of the file ...");
+            segment.setString(1048576-32, "Here is the end of the file ...");
+            
+            // read some data
+            System.out.println(segment.getString(0));
+        }
+        
+        System.out.println("\n\nYou should find the files on disk in the project's root");
+    }
+}