Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, * software distributed under the License is distributed on an * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY * KIND, either express or implied. See the License for the * specific language governing permissions and limitations * under the License. */ package org.apache.cassandra.utils; import java.io.BufferedReader; import java.io.File; import java.io.FileDescriptor; import java.io.IOException; import java.io.InputStreamReader; import java.lang.reflect.Field; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.apache.commons.lang.StringUtils; import com.sun.jna.LastErrorException; import com.sun.jna.Native; public final class CLibrary { private static Logger logger = LoggerFactory.getLogger(CLibrary.class); private static final int MCL_CURRENT = 1; private static final int MCL_FUTURE = 2; private static final int ENOMEM = 12; private static final int F_GETFL = 3; /* get file status flags */ private static final int F_SETFL = 4; /* set file status flags */ private static final int F_NOCACHE = 48; /* Mac OS X specific flag, turns cache on/off */ private static final int O_DIRECT = 040000; /* fcntl.h */ private static final int O_RDONLY = 00000000; /* fcntl.h */ private static final int POSIX_FADV_NORMAL = 0; /* fadvise.h */ private static final int POSIX_FADV_RANDOM = 1; /* fadvise.h */ private static final int POSIX_FADV_SEQUENTIAL = 2; /* fadvise.h */ private static final int POSIX_FADV_WILLNEED = 3; /* fadvise.h */ private static final int POSIX_FADV_DONTNEED = 4; /* fadvise.h */ private static final int POSIX_FADV_NOREUSE = 5; /* fadvise.h */ static { try { Native.register("c"); } catch (NoClassDefFoundError e) { logger.info("JNA not found. Native methods will be disabled."); } catch (UnsatisfiedLinkError e) { logger.info("Unable to link C library. Native methods will be disabled."); } catch (NoSuchMethodError e) { logger.warn( "Obsolete version of JNA present; unable to register C library. Upgrade to JNA 3.2.7 or later"); } } private static native int mlockall(int flags) throws LastErrorException; private static native int munlockall() throws LastErrorException; private static native int link(String from, String to) throws LastErrorException; // fcntl - manipulate file descriptor, `man 2 fcntl` public static native int fcntl(int fd, int command, long flags) throws LastErrorException; // fadvice public static native int posix_fadvise(int fd, long offset, int len, int flag) throws LastErrorException; public static native int open(String path, int flags) throws LastErrorException; public static native int fsync(int fd) throws LastErrorException; public static native int close(int fd) throws LastErrorException; private static int errno(RuntimeException e) { assert e instanceof LastErrorException; try { return ((LastErrorException) e).getErrorCode(); } catch (NoSuchMethodError x) { logger.warn("Obsolete version of JNA present; unable to read errno. Upgrade to JNA 3.2.7 or later"); return 0; } } private CLibrary() { } public static void tryMlockall() { try { int result = mlockall(MCL_CURRENT); assert result == 0; // mlockall should always be zero on success logger.info("JNA mlockall successful"); } catch (UnsatisfiedLinkError e) { // this will have already been logged by CLibrary, no need to repeat it } catch (RuntimeException e) { if (!(e instanceof LastErrorException)) throw e; if (errno(e) == ENOMEM && System.getProperty("os.name").toLowerCase().contains("linux")) { logger.warn("Unable to lock JVM memory (ENOMEM)." + " This can result in part of the JVM being swapped out, especially with mmapped I/O enabled." + " Increase RLIMIT_MEMLOCK or run Cassandra as root."); } else if (!System.getProperty("os.name").toLowerCase().contains("mac")) { // OS X allows mlockall to be called, but always returns an error logger.warn("Unknown mlockall error " + errno(e)); } } } /** * Create a hard link for a given file. * * @param sourceFile The name of the source file. * @param destinationFile The name of the destination file. * * @throws java.io.IOException if an error has occurred while creating the link. */ public static void createHardLink(File sourceFile, File destinationFile) throws IOException { try { int result = link(sourceFile.getAbsolutePath(), destinationFile.getAbsolutePath()); assert result == 0; // success is always zero } catch (UnsatisfiedLinkError e) { createHardLinkWithExec(sourceFile, destinationFile); } catch (RuntimeException e) { logger.error("Unable to create hard link", e); if (!(e instanceof LastErrorException)) throw e; // there are 17 different error codes listed on the man page. punt until/unless we find which // ones actually turn up in practice. throw new IOException(String.format("Unable to create hard link from %s to %s (errno %d)", sourceFile, destinationFile, errno(e))); } } public static void createHardLinkWithExec(File sourceFile, File destinationFile) throws IOException { String osname = System.getProperty("os.name"); ProcessBuilder pb; if (osname.startsWith("Windows")) { float osversion = Float.parseFloat(System.getProperty("os.version")); if (osversion >= 6.0f) { pb = new ProcessBuilder("cmd", "/c", "mklink", "/H", destinationFile.getAbsolutePath(), sourceFile.getAbsolutePath()); } else { pb = new ProcessBuilder("fsutil", "hardlink", "create", destinationFile.getAbsolutePath(), sourceFile.getAbsolutePath()); } } else { pb = new ProcessBuilder("ln", sourceFile.getAbsolutePath(), destinationFile.getAbsolutePath()); pb.redirectErrorStream(true); } try { exec(pb); } catch (IOException ex) { logger.error("Unable to create hard link", ex); throw ex; } } private static void exec(ProcessBuilder pb) throws IOException { Process p = pb.start(); try { int errCode = p.waitFor(); if (errCode != 0) { BufferedReader in = new BufferedReader(new InputStreamReader(p.getInputStream())); BufferedReader err = new BufferedReader(new InputStreamReader(p.getErrorStream())); StringBuffer buff = new StringBuffer(); String str; while ((str = in.readLine()) != null) buff.append(str).append(System.getProperty("line.separator")); while ((str = err.readLine()) != null) buff.append(str).append(System.getProperty("line.separator")); throw new IOException( "Exception while executing the command: " + StringUtils.join(pb.command(), " ") + ", command error Code: " + errCode + ", command output: " + buff.toString()); } } catch (InterruptedException e) { throw new RuntimeException(e); } } public static void trySkipCache(int fd, long offset, int len) { if (fd < 0) return; try { if (System.getProperty("os.name").toLowerCase().contains("linux")) { posix_fadvise(fd, offset, len, POSIX_FADV_DONTNEED); } } catch (UnsatisfiedLinkError e) { // if JNA is unavailable just skipping Direct I/O // instance of this class will act like normal RandomAccessFile } } public static int tryFcntl(int fd, int command, int flags) { int result = -1; try { result = CLibrary.fcntl(fd, command, flags); assert result >= 0; // on error a value of -1 is returned and errno is set to indicate the error. } catch (RuntimeException e) { if (!(e instanceof LastErrorException)) throw e; logger.warn( String.format("fcntl(%d, %d, %d) failed, errno (%d).", fd, command, flags, CLibrary.errno(e))); } return result; } public static int tryOpenDirectory(String path) { int fd = -1; try { return open(path, O_RDONLY); } catch (UnsatisfiedLinkError e) { // JNA is unavailable just skipping Direct I/O } catch (RuntimeException e) { if (!(e instanceof LastErrorException)) throw e; logger.warn(String.format("open(%s, O_RDONLY) failed, errno (%d).", path, CLibrary.errno(e))); } return fd; } public static void trySync(int fd) { if (fd == -1) return; try { fsync(fd); } catch (UnsatisfiedLinkError e) { // JNA is unavailable just skipping Direct I/O } catch (RuntimeException e) { if (!(e instanceof LastErrorException)) throw e; logger.warn(String.format("fsync(%d) failed, errno (%d).", fd, CLibrary.errno(e))); } } public static void tryCloseFD(int fd) { if (fd == -1) return; try { close(fd); } catch (UnsatisfiedLinkError e) { // JNA is unavailable just skipping Direct I/O } catch (RuntimeException e) { if (!(e instanceof LastErrorException)) throw e; logger.warn(String.format("close(%d) failed, errno (%d).", fd, CLibrary.errno(e))); } } /** * Get system file descriptor from FileDescriptor object. * @param descriptor - FileDescriptor objec to get fd from * @return file descriptor, -1 or error */ public static int getfd(FileDescriptor descriptor) { Field field = FBUtilities.getProtectedField(descriptor.getClass(), "fd"); if (field == null) return -1; try { return field.getInt(descriptor); } catch (Exception e) { logger.warn("unable to read fd field from FileDescriptor"); } return -1; } }