Fix some concurrency issues in LoadLibrary.java

lib/src/main/java/org/automerge/LoadLibrary.java

@@ -6,13 +6,13 @@
 import java.nio.file.*;
 import java.util.Locale;
 import java.util.Optional;
-import java.util.Properties;
 import java.util.UUID;
 import java.util.stream.Stream;
 
-class LoadLibrary {
+public class LoadLibrary {
 
     private static class Library {
+
         public String target;
         public String prefix;
         public String suffix;
@@ -124,16 +124,44 @@ public boolean isAndroid() {
     // The extension added to the library name to create a lockfile for it
     private static final String LIBRARY_LOCK_EXT = ".lck";
 
-    static boolean loaded = false;
+    static volatile boolean loaded = false;
+    static volatile boolean versionChecked = false;
 
-    public static synchronized void initialize() {
-        // Only do this on first load and _dont_ do it on android, where libraries
-        // are provided by jniLibs and the version.properties file is removed from the
-        // jar by the build process
-        if (!loaded && !CURRENT_PLATFORM.isAndroid()) {
-            cleanup();
+    public static void initialize() {
+        // Early return if already loaded and version checked
+        if (loaded && versionChecked) {
+            return;
+        }
+
+        synchronized (LoadLibrary.class) {
+            // Double-check after acquiring lock
+            if (loaded && versionChecked) {
+                return;
+            }
+
+            // Load the library if not already loaded
+            if (!loaded) {
+                // Only do this on first load and _dont_ do it on android, where libraries
+                // are provided by jniLibs
+                if (!CURRENT_PLATFORM.isAndroid()) {
+                    cleanup();
+                }
+                loadAutomergeJniLib();
+                loaded = true;
+            }
+        }
+
+        // Perform version check OUTSIDE the synchronized block to avoid deadlock
+        // when AutomergeSys static initializer calls back to initialize()
+        if (!versionChecked) {
+            String expectedLibVersion = BuildInfo.getExpectedRustLibVersion();
+            String actualLibVersion = AutomergeSys.rustLibVersion();
+            if (!expectedLibVersion.equals(actualLibVersion)) {
+                throw new RuntimeException("Automerge native library version mismatch. Expected " + expectedLibVersion
+                        + " but got " + actualLibVersion);
+            }
+            versionChecked = true;
         }
-        loadAutomergeJniLib();
     }
 
     private static File getTempDir() {
@@ -152,7 +180,7 @@ private static File getTempDir() {
      * instances of the JVM which have loaded the library.
      */
     static void cleanup() {
-        String searchPattern = "automerge-jni-" + getVersion();
+        String searchPattern = "automerge-jni-" + BuildInfo.getExpectedRustLibVersion();
 
         try (Stream<Path> dirList = Files.list(getTempDir().toPath())) {
             dirList.filter(path -> !path.getFileName().toString().endsWith(LIBRARY_LOCK_EXT)
@@ -173,7 +201,7 @@ static void cleanup() {
 
     private static void extractAndLoadLibraryFile(Library library, String targetFolder) {
         String uuid = UUID.randomUUID().toString();
-        String extractedLibFileName = String.format("automerge-jni-%s-%s-%s.%s", getVersion(), uuid, library.target,
+        String extractedLibFileName = String.format("automerge-jni-%s-%s-%s.%s", BuildInfo.getExpectedRustLibVersion(), uuid, library.target,
                 library.suffix);
         String extractedLckFileName = extractedLibFileName + LIBRARY_LOCK_EXT;
 
@@ -230,17 +258,16 @@ private static InputStream getResourceAsStream(String name) {
      * <p>
      * We first try the system library path, then if that fails we try and load one
      * of the bundled libraries from this jar.
+     *
+     * <p>
+     * Note: This method does NOT set the loaded flag. That is the responsibility
+     * of the caller (initialize() method) to ensure proper synchronization.
      */
     private static void loadAutomergeJniLib() {
-        if (loaded) {
-            return;
-        }
-
         String libName = "automerge_jni_" + BuildInfo.getExpectedRustLibVersion().replace('.', '_');
         // Try System.loadLibrary first
         try {
             System.loadLibrary(libName);
-            loaded = true;
             return;
         } catch (UnsatisfiedLinkError e) {
             if (CURRENT_PLATFORM.isAndroid()) {
@@ -259,31 +286,5 @@ private static void loadAutomergeJniLib() {
         Library lib = CURRENT_PLATFORM.library().get();
         // Try extracting the library from jar
         extractAndLoadLibraryFile(lib, tempFolder);
-
-        // Check that we have the correct version of the library (BuildInfo is
-        // generated by gradle and contains the version of the rust library we
-        // were built against)
-        String expectedLibVersion = BuildInfo.getExpectedRustLibVersion();
-        String actualLibVersion = AutomergeSys.rustLibVersion();
-        if (!expectedLibVersion.equals(actualLibVersion)) {
-            throw new RuntimeException("Automerge native library version mismatch. Expected " + expectedLibVersion
-                    + " but got " + actualLibVersion);
-        }
-
-        loaded = true;
-    }
-
-    public static String getVersion() {
-        InputStream input = getResourceAsStream("version.properties");
-
-        String version = "unknown";
-        try {
-            Properties versionData = new Properties();
-            versionData.load(input);
-            version = versionData.getProperty("version", version);
-            return version;
-        } catch (IOException e) {
-            throw new RuntimeException("unable to load version properties", e);
-        }
     }
 }