nativeaccess: try to load all located libsystemds (#108238)

Linux systems with multiarch (e.g. i386 & x86_64) libraries
may have libsystemd.0 in two subdirectories of an entry in
java.library.path. For example, libsystemd.so.0 may be found
in both /usr/lib/i386-linux-gnu and /usr/lib/x86_64-linux-gnu.

Instead of attempting to load any library found, attempt all
and stop as soon as one is successfully loaded.

docs/changelog/108238.yaml

@@ -0,0 +1,6 @@
+pr: 108238
+summary: "Nativeaccess: try to load all located libsystemds"
+area: Infra/Core
+type: bug
+issues:
+ - 107878

libs/native/src/main21/java/org/elasticsearch/nativeaccess/jdk/JdkSystemdLibrary.java

@@ -17,7 +17,10 @@
 import java.lang.foreign.MemorySegment;
 import java.lang.invoke.MethodHandle;
 import java.nio.file.Files;
+import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.util.Arrays;
+import java.util.List;
 
 import static java.lang.foreign.ValueLayout.ADDRESS;
 import static java.lang.foreign.ValueLayout.JAVA_INT;
@@ -26,31 +29,49 @@
 class JdkSystemdLibrary implements SystemdLibrary {
 
     static {
-        System.load(findLibSystemd());
-    }
-
-    // On some systems libsystemd does not have a non-versioned symlink. System.loadLibrary only knows how to find
-    // non-versioned library files. So we must manually check the library path to find what we need.
-    static String findLibSystemd() {
-        final String libsystemd = "libsystemd.so.0";
-        String libpath = System.getProperty("java.library.path");
-        for (String basepathStr : libpath.split(":")) {
-            var basepath = Paths.get(basepathStr);
-            if (Files.exists(basepath) == false) {
-                continue;
+        // Find and load libsystemd. We attempt all instances of
+        // libsystemd in case of multiarch systems, and stop when
+        // one is successfully loaded. If none can be loaded,
+        // UnsatisfiedLinkError will be thrown.
+        List<String> paths = findLibSystemd();
+        if (paths.isEmpty()) {
+            String libpath = System.getProperty("java.library.path");
+            throw new UnsatisfiedLinkError("Could not find libsystemd in java.library.path: " + libpath);
+        }
+        UnsatisfiedLinkError last = null;
+        for (String path : paths) {
+            try {
+                System.load(path);
+                last = null;
+                break;
+            } catch (UnsatisfiedLinkError e) {
+                last = e;
             }
-            try (var stream = Files.walk(basepath)) {
+        }
+        if (last != null) {
+            throw last;
+        }
+    }
 
-                var foundpath = stream.filter(Files::isDirectory).map(p -> p.resolve(libsystemd)).filter(Files::exists).findAny();
-                if (foundpath.isPresent()) {
-                    return foundpath.get().toAbsolutePath().toString();
-                }
+    // findLibSystemd returns a list of paths to instances of libsystemd
+    // found within java.library.path.
+    static List<String> findLibSystemd() {
+        // Note: on some systems libsystemd does not have a non-versioned symlink.
+        // System.loadLibrary only knows how to find non-versioned library files,
+        // so we must manually check the library path to find what we need.
+        final Path libsystemd = Paths.get("libsystemd.so.0");
+        final String libpath = System.getProperty("java.library.path");
+        return Arrays.stream(libpath.split(":")).map(Paths::get).filter(Files::exists).flatMap(p -> {
+            try {
+                return Files.find(
+                    p,
+                    Integer.MAX_VALUE,
+                    (fp, attrs) -> (attrs.isDirectory() == false && fp.getFileName().equals(libsystemd))
+                );
             } catch (IOException e) {
                 throw new UncheckedIOException(e);
             }
-
-        }
-        throw new UnsatisfiedLinkError("Could not find " + libsystemd + " in java.library.path: " + libpath);
+        }).map(p -> p.toAbsolutePath().toString()).toList();
     }
 
     private static final MethodHandle sd_notify$mh = downcallHandle("sd_notify", FunctionDescriptor.of(JAVA_INT, JAVA_INT, ADDRESS));