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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
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.io.SyncFailedException;
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;
/**
* Provides functionality only possible through native C library.
*/
public class NativeIO {
private final static Logger logger = Logger.getLogger(NativeIO.class.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 static final Field fieldFD = getField(FileDescriptor.class, "fd");
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 " + getError().getMessage());
}
}
public boolean valid() { return initialized; }
public Throwable getError() {
if (initError != null) {
return initError;
} else {
return new RuntimeException("Platform is unsúpported. Only supported on linux.");
}
}
/**
* Will hint the OS that data read so far will not be accessed again and should hence be dropped from the buffer cache.
* @param fd The file descriptor to drop from buffer cache.
*/
public void dropPartialFileFromCache(FileDescriptor fd, long offset, long len, boolean sync) {
if (sync) {
try {
fd.sync();
} catch (SyncFailedException e) {
logger.warning("Sync failed while dropping cache: " + e.getMessage());
}
}
if (initialized) {
posix_fadvise(getNativeFD(fd), offset, len, POSIX_FADV_DONTNEED);
}
}
/**
* Will hint the OS that this is will not be accessed again and should hence be dropped from the buffer cache.
* @param fd The file descriptor to drop from buffer cache.
*/
public void dropFileFromCache(FileDescriptor fd) {
dropPartialFileFromCache(fd, 0, 0, true);
}
/**
* Will hint the OS that this is will not be accessed again and should hence be dropped from the buffer cache.
* @param file File to drop from buffer cache
*/
public void dropFileFromCache(File file) {
try {
dropFileFromCache(new FileInputStream(file).getFD());
} catch (FileNotFoundException e) {
logger.fine("No point in dropping a non-existing file from the buffer cache: " + e.getMessage());
} 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 static int getNativeFD(FileDescriptor fd) {
try {
return fieldFD.getInt(fd);
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
}
}
}
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