Foreign (Function) Memory API

Author: AnghelLeonard

Chapter07/JDK 22/P165_CallingGetpid/README.md

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+# Introducing Foreign Linker API:
+Provide a brief description of Foreign Linker API including Linker, SymbolLookup, downcall, and upcall.
+
+## Using JDK 21

Chapter07/JDK 22/P165_CallingGetpid/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>P165_CallingGetpid</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>P165_CallingGetpid</name>    
+</project>

Chapter07/JDK 22/P165_CallingGetpid/src/main/java/modern/challenge/Main.java

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+package modern.challenge;
+
+import java.lang.foreign.FunctionDescriptor;
+import java.lang.foreign.Linker;
+import java.lang.foreign.MemorySegment;
+import java.lang.foreign.SymbolLookup;
+import java.lang.foreign.ValueLayout;
+import java.lang.invoke.MethodHandle;
+
+public class Main {
+
+    public static void main(String[] args) throws Throwable {
+
+        // get the Linker of the underlying native platform 
+        // (operating system + processor that runs the JVM)
+        Linker linker = Linker.nativeLinker();
+        
+        // "_getpid" is part of the Universal C Runtime (UCRT) Library
+        SymbolLookup libLookup = linker.defaultLookup();
+        
+        // find the "_getpid" foreign function
+        MemorySegment segmentGetpid = libLookup.find("_getpid").get();
+
+        // create a method handle for "_getpid"
+        MethodHandle func = linker.downcallHandle(segmentGetpid,
+                FunctionDescriptor.of(ValueLayout.JAVA_INT));
+
+        // invoke the foreign function, "_getpid" and get the result
+        int result = (int) func.invokeExact();       
+        System.out.println(result);
+    }
+}

Chapter07/JDK 22/P166_CallingSumTwoInt/README.md

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+# Calling the sumTwoInt() foreign function:
+Write a Java application that calls the sumTwoInt() method (the long sumTwoInt(int x, int y) implemented in Problem 144) via the Foreign Linker API.
+
+## Using JDK 21

Chapter07/JDK 22/P166_CallingSumTwoInt/lib/cpp/Arithmetic.o

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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>P166_CallingSumTwoInt</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>P166_CallingSumTwoInt</name>    
+</project>

Chapter07/JDK 22/P166_CallingSumTwoInt/lib/cpp/math.dll

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+package modern.challenge;
+
+import java.lang.foreign.Arena;
+import java.lang.foreign.FunctionDescriptor;
+import java.lang.foreign.Linker;
+import java.lang.foreign.MemorySegment;
+import java.lang.foreign.SymbolLookup;
+import java.lang.foreign.ValueLayout;
+import java.lang.invoke.MethodHandle;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+public class Main {
+
+    public static void main(String[] args) throws Throwable {
+
+        Linker linker = Linker.nativeLinker();
+        Path path = Paths.get("lib/cpp/math.dll");            
+       
+        try (Arena arena = Arena.ofConfined()) {                        
+            
+            SymbolLookup libLookup = SymbolLookup.libraryLookup(path, arena);            
+            MemorySegment segmentSumTwoInt = libLookup.find("_Z9sumTwoIntii").get();
+
+            MethodHandle func = linker.downcallHandle(segmentSumTwoInt,
+                    FunctionDescriptor.of(ValueLayout.JAVA_LONG, ValueLayout.JAVA_INT, ValueLayout.JAVA_INT));
+
+            long result = (long) func.invokeExact(3, 9);
+
+            System.out.println(result);
+        }
+    }
+}

Chapter07/JDK 22/P166_CallingSumTwoInt/pom.xml

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+#include <iostream>
+#include "Arithmetic.h"
+
+long sumTwoInt(int x, int y) {
+    std::cout << "C++: The received arguments are : " << x << " and " << y << std::endl;
+    return (long)x + (long)y;
+}

Chapter07/JDK 22/P166_CallingSumTwoInt/src/main/java/modern/challenge/Main.java

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+ #ifndef FUNCTIONS_H_INCLUDED
+ #define FUNCTIONS_H_INCLUDED
+
+  long sumTwoInt(int x, int y);  // Function prototype, its declaration
+
+  #endif