Changed NativeLibraryLocator to make extraction code multi-process safe.

src/main/java/net/rubygrapefruit/platform/Native.java

@@ -19,22 +19,17 @@ public class Native {
     private Native() {
     }
 
-    /**
-     * Returns the version of the native library implementations used by this class.
-     */
-    @ThreadSafe
-    static public String getNativeVersion() {
-        return String.valueOf(NativeLibraryFunctions.VERSION);
-    }
-
     /**
      * Initialises the native integration, if not already initialized.
      *
      * @param extractDir The directory to extract native resources into. May be null, in which case a default is
      * selected.
+     *
+     * @throws NativeIntegrationUnavailableException When native integration is not available on the current machine.
+     * @throws NativeException On failure to load the native integration.
      */
     @ThreadSafe
-    static public void init(File extractDir) {
+    static public void init(File extractDir) throws NativeIntegrationUnavailableException, NativeException {
         synchronized (Native.class) {
             if (!loaded) {
                 Platform platform = Platform.current();

src/main/java/net/rubygrapefruit/platform/internal/NativeLibraryLocator.java

@@ -1,9 +1,11 @@
 package net.rubygrapefruit.platform.internal;
 
 import net.rubygrapefruit.platform.NativeException;
+import net.rubygrapefruit.platform.internal.jni.NativeLibraryFunctions;
 
 import java.io.*;
 import java.net.URL;
+import java.nio.channels.FileLock;
 
 public class NativeLibraryLocator {
     private final File extractDir;
@@ -13,22 +15,47 @@ public class NativeLibraryLocator {
     }
 
     public File find(String libraryName) throws IOException {
-        File libFile;
-        URL resource = getClass().getClassLoader().getResource(libraryName);
-        if (resource != null) {
-            File libDir = extractDir;
-            if (libDir == null) {
-                libDir = File.createTempFile("native-platform", "dir");
+        if (extractDir != null) {
+            File libFile = new File(extractDir, String.format("%s/%s", NativeLibraryFunctions.VERSION, libraryName));
+            File lockFile = new File(libFile.getParentFile(), libFile.getName() + ".lock");
+            lockFile.getParentFile().mkdirs();
+            lockFile.createNewFile();
+            RandomAccessFile lockFileAccess = new RandomAccessFile(lockFile, "rw");
+            try {
+                // Take exclusive lock on lock file
+                FileLock lock = lockFileAccess.getChannel().lock();
+                if (lockFile.length() > 0 && lockFileAccess.readBoolean()) {
+                    // Library has been extracted
+                    return libFile;
+                }
+                URL resource = getClass().getClassLoader().getResource(libraryName);
+                if (resource != null) {
+                    // Extract library and write marker to lock file
+                    libFile.getParentFile().mkdirs();
+                    copy(resource, libFile);
+                    lockFileAccess.seek(0);
+                    lockFileAccess.writeBoolean(true);
+                    return libFile;
+                }
+            } finally {
+                // Also releases lock
+                lockFileAccess.close();
+            }
+        } else {
+            URL resource = getClass().getClassLoader().getResource(libraryName);
+            if (resource != null) {
+                File libFile;
+                File libDir = File.createTempFile("native-platform", "dir");
                 libDir.delete();
                 libDir.mkdirs();
+                libFile = new File(libDir, libraryName);
+                libFile.deleteOnExit();
+                copy(resource, libFile);
+                return libFile;
             }
-            libFile = new File(libDir, libraryName);
-            libFile.deleteOnExit();
-            copy(resource, libFile);
-            return libFile;
         }
 
-        libFile = new File("build/binaries/" + libraryName);
+        File libFile = new File("build/binaries/" + libraryName);
         if (libFile.isFile()) {
             return libFile;
         }