USE jna to provide access to native fadvise system call

2 files changed, 118 insertions, 0 deletions

diff --git a/vespajlib/src/main/java/com/yahoo/io/NativeIO.java b/vespajlib/src/main/java/com/yahoo/io/NativeIO.java
new file mode 100644
index 00000000000..5adb509ac3b
--- /dev/null
+++ b/vespajlib/src/main/java/com/yahoo/io/NativeIO.java
@@ -0,0 +1,83 @@
+package com.yahoo.io;
+
+import java.io.File;
+import java.io.FileDescriptor;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.lang.reflect.Field;
+import java.util.logging.Logger;
+
+import com.sun.jna.LastErrorException;
+import com.sun.jna.Native;
+import com.sun.jna.Platform;
+
+public class NativeIO {
+    private final Logger logger = Logger.getLogger(getClass().getName());
+    private static final int POSIX_FADV_DONTNEED = 4; // See /usr/include/linux/fadvise.h
+    private static boolean initialized = false;
+    private static Throwable initError = null;
+    static {
+        try {
+            if (Platform.isLinux()) {
+                Native.register(Platform.C_LIBRARY_NAME);
+                initialized = true;
+            }
+        } catch (Throwable throwable) {
+            initError = throwable;
+        }
+    }
+
+    private final Field fieldFD;
+
+    private static native int posix_fadvise(int fd, long offset, long len, int flag) throws LastErrorException;
+
+    public NativeIO() {
+        if (!initialized) {
+            logger.warning("native IO not possible due to " + initError);
+            if (initError != null) {
+                throw new RuntimeException(initError);
+            } else {
+                throw new RuntimeException("Platform is unsúpported. Only supported on linux.");
+            }
+        }
+        fieldFD = getField(FileDescriptor.class, "fd");
+    }
+
+    public void dropFileFromCache(FileDescriptor fd) {
+        if (initialized) {
+            posix_fadvise(getfh(fd), 0, 0, POSIX_FADV_DONTNEED);
+        }
+    }
+
+    public void dropFileFromCache(File file) {
+        try {
+            dropFileFromCache(new FileInputStream(file).getFD());
+        } catch (FileNotFoundException e) {
+            throw new RuntimeException(e);
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+
+    private static Field getField(Class<?> clazz, String fieldName) {
+        Field field;
+        try {
+            field = clazz.getDeclaredField(fieldName);
+        } catch (NoSuchFieldException e) {
+            throw new RuntimeException(e);
+        }
+        field.setAccessible(true);
+        return field;
+    }
+
+    private int getfh(FileDescriptor fd) {
+        try {
+            return fieldFD.getInt(fd);
+        } catch (IllegalAccessException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+}
diff --git a/vespajlib/src/test/java/com/yahoo/io/NativeIOTestCase.java b/vespajlib/src/test/java/com/yahoo/io/NativeIOTestCase.java
new file mode 100644
index 00000000000..91144d5999f
--- /dev/null
+++ b/vespajlib/src/test/java/com/yahoo/io/NativeIOTestCase.java
@@ -0,0 +1,35 @@
+package com.yahoo.io;
+
+import com.sun.jna.Platform;
+import org.junit.Test;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+
+public class NativeIOTestCase {
+
+    @Test
+    public void requireThatDropFileFromCacheDoesNotThrow() throws IOException {
+        File testFile = new File("testfile");
+        FileOutputStream output = new FileOutputStream(testFile);
+        output.write('t');
+        output.flush();
+        output.close();
+        try {
+            NativeIO nativeIO = new NativeIO();
+            nativeIO.dropFileFromCache(output.getFD());
+            nativeIO.dropFileFromCache(testFile);
+        } catch (Throwable e) {
+            if (Platform.isLinux()) {
+                assertTrue(false);
+            } else {
+                assertEquals("Platform is unsúpported. Only supported on linux.", e.getMessage());
+            }
+        }
+    }
+}