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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 com.yahoo.nativec.PosixFAdvise;
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;
/**
* Provides functionality only possible through native C library.
*/
public class NativeIO {
private static final Logger logger = Logger.getLogger(NativeIO.class.getName());
private static final String DISABLE_NATIVE_IO = "DISABLE_NATIVE_IO";
private static final InitResult fdField = new InitResult();
private static class InitResult {
private final boolean initialized;
private final boolean enabled;
private final Field fdField;
private final Throwable initError;
InitResult() {
boolean initComplete = false;
boolean disabled = true;
Field field = null;
Throwable exception = null;
try {
exception = PosixFAdvise.init();
if (exception == null) {
disabled = System.getenv().containsKey(DISABLE_NATIVE_IO);
if (!disabled) {
field = getField(FileDescriptor.class, "fd");
initComplete = true;
}
}
} catch (Throwable throwable) {
exception = throwable;
}
initialized = initComplete;
enabled = ! disabled;
initError = exception;
fdField = field;
}
private static Field getField(Class<?> clazz, String fieldName) throws NoSuchFieldException {
Field field = clazz.getDeclaredField(fieldName);
field.setAccessible(true);
return field;
}
boolean isInitialized() { return initialized; }
boolean isEnabled() { return enabled; }
Throwable getError() { return initError; }
int getNativeFD(FileDescriptor fd) {
try {
return fdField.getInt(fd);
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
}
}
}
public NativeIO() {
if ( ! fdField.isInitialized()) {
if (fdField.isEnabled()) {
logger.warning("Native IO not possible due to " + getError().getMessage());
} else {
logger.info("Native IO has been disabled explicit via system property " + DISABLE_NATIVE_IO);
}
}
}
public boolean valid() { return fdField.isInitialized(); }
public final Throwable getError() { return fdField.getError(); }
/**
* 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 (valid()) {
PosixFAdvise.posix_fadvise(fdField.getNativeFD(fd), offset, len, PosixFAdvise.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);
}
}
}
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