content: /*
   * 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.asterix.transaction.management.service.logging;
  
  import java.io.IOException;
  import java.nio.ByteBuffer;
  
  import org.apache.asterix.common.exceptions.ACIDException;
  import org.apache.asterix.common.transactions.ILogManager;
  import org.apache.asterix.common.transactions.ILogReader;
  import org.apache.asterix.common.transactions.ILogRecord;
  import org.apache.asterix.common.transactions.ILogRecord.RecordReadStatus;
  import org.apache.asterix.common.transactions.LogRecord;
  import org.apache.asterix.common.transactions.MutableLong;
  import org.apache.asterix.common.transactions.TxnLogFile;
  import org.apache.hyracks.util.annotations.NotThreadSafe;
  import org.apache.logging.log4j.LogManager;
  import org.apache.logging.log4j.Logger;
  
  @NotThreadSafe
  public class LogReader implements ILogReader {
  
      private static final Logger LOGGER = LogManager.getLogger();
      private final ILogManager logMgr;
      private final long logFileSize;
      private final int logPageSize;
      private final MutableLong flushLSN;
      private final boolean isRecoveryMode;
      private final ByteBuffer readBuffer;
      private final ILogRecord logRecord;
      private long readLSN;
      private long bufferBeginLSN;
      private long fileBeginLSN;
      private TxnLogFile logFile;
  
      private enum ReturnState {
          FLUSH,
          EOF
      }
  
      public LogReader(ILogManager logMgr, long logFileSize, int logPageSize, MutableLong flushLSN,
              boolean isRecoveryMode) {
          this.logMgr = logMgr;
          this.logFileSize = logFileSize;
          this.logPageSize = logPageSize;
          this.flushLSN = flushLSN;
          this.isRecoveryMode = isRecoveryMode;
          this.readBuffer = ByteBuffer.allocate(logPageSize);
          this.logRecord = new LogRecord();
      }
  
      @Override
      public void setPosition(long lsn) {
          readLSN = lsn;
          if (waitForFlushOrReturnIfEOF() == ReturnState.EOF) {
              return;
          }
          getLogFile();
          fillLogReadBuffer();
      }
  
      /**
       * Get the next log record from the log file.
       *
       * @return A deserialized log record, or null if we have reached the end of the file.
       * @throws ACIDException
       */
      @Override
      public ILogRecord next() {
          if (waitForFlushOrReturnIfEOF() == ReturnState.EOF) {
              return null;
          }
          if (readBuffer.position() == readBuffer.limit()) {
              boolean hasRemaining = refillLogReadBuffer();
              if (!hasRemaining && isRecoveryMode && readLSN < flushLSN.get()) {
                  LOGGER.error("Transaction log ends before expected. Log files may be missing.");
                  return null;
              }
          }
          ByteBuffer readBuffer = this.readBuffer;
          boolean refilled = false;
  
          while (true) {
              RecordReadStatus status = logRecord.readLogRecord(readBuffer);
              switch (status) {
                  case TRUNCATED: {
                      if (!refilled) {
                          //we may have just read off the end of the buffer, so try refiling it
                          if (!refillLogReadBuffer()) {
                              return null;
                          }
                          refilled = true;
                          //now see what we have in the refilled buffer
                          continue;
                      } else {
                          LOGGER.info("Log file has truncated log records.");
                          return null;
                      }
                  }
                  case LARGE_RECORD: {
                      readBuffer = ByteBuffer.allocate(logRecord.getLogSize());
                      fillLogReadBuffer(logRecord.getLogSize(), readBuffer);
                      //now see what we have in the expanded buffer
                      continue;
                  }
                  case BAD_CHKSUM: {
                      LOGGER.error(
                              "Transaction log contains corrupt log records (perhaps due to medium error). Stopping recovery early.");
                      return null;
                  }
                  case OK:
                      break;
                  default:
                      throw new IllegalStateException("Unexpected log read status: " + status);
  
              }
              // break the loop by default
              break;
          }
          logRecord.setLSN(readLSN);
          readLSN += logRecord.getLogSize();
          return logRecord;
      }
  
      private ReturnState waitForFlushOrReturnIfEOF() {
          synchronized (flushLSN) {
              while (readLSN >= flushLSN.get()) {
                  if (isRecoveryMode) {
                      return ReturnState.EOF;
                  }
                  try {
                      flushLSN.wait();
                  } catch (InterruptedException e) {
                      Thread.currentThread().interrupt();
                      throw new ACIDException(e);
                  }
              }
              return ReturnState.FLUSH;
          }
      }
  
      /**
       * Continues log analysis between log file splits.
       *
       * @return true if log continues, false if EOF
       * @throws ACIDException
       */
      private boolean refillLogReadBuffer() {
          try {
              if (logFile.size() > 0 && readLSN % logFileSize == logFile.size()) {
                  readLSN += logFileSize - (readLSN % logFileSize);
                  getLogFile();
              }
              return fillLogReadBuffer();
          } catch (IOException e) {
              throw new ACIDException(e);
          }
      }
  
      /**
       * Fills the log buffer with data from the log file at the current position
       *
       * @return false if EOF, true otherwise
       */
      private boolean fillLogReadBuffer() {
          return fillLogReadBuffer(logPageSize, readBuffer);
      }
  
      private boolean fillLogReadBuffer(int readSize, ByteBuffer readBuffer) {
          int size = 0;
          int read = 0;
          readBuffer.position(0);
          readBuffer.limit(readSize);
          try {
              logFile.position(readLSN % logFileSize);
              //We loop here because read() may return 0, but this simply means we are waiting on IO.
              //Therefore we want to break out only when either the buffer is full, or we reach EOF.
              while (size < readSize && read != -1) {
                  read = logFile.read(readBuffer);
                  if (read > 0) {
                      size += read;
                  }
              }
          } catch (IOException e) {
              throw new ACIDException(e);
          }
          readBuffer.position(0);
          readBuffer.limit(size);
          if (size == 0 && read == -1) {
              return false; //EOF
          }
          bufferBeginLSN = readLSN;
          return true;
      }
  
      @Override
      public ILogRecord read(long lsn) {
          readLSN = lsn;
          //wait for the log to be flushed if needed before trying to read it.
          synchronized (flushLSN) {
              while (readLSN >= flushLSN.get()) {
                  try {
                      flushLSN.wait();
                  } catch (InterruptedException e) {
                      Thread.currentThread().interrupt();
                      throw new ACIDException(e);
                  }
              }
          }
          try {
              if (logFile == null || readLSN < fileBeginLSN || readLSN >= fileBeginLSN + logFile.size()) {
                  //get the log file which contains readLSN
                  getLogFile();
                  fillLogReadBuffer();
              } else if (readLSN < bufferBeginLSN || readLSN >= bufferBeginLSN + readBuffer.limit()) {
                  //log is not in the current read buffer
                  fillLogReadBuffer();
              } else {
                  //log is either completely in the current read buffer or truncated
                  readBuffer.position((int) (readLSN - bufferBeginLSN));
              }
          } catch (IOException e) {
              throw new ACIDException(e);
          }
  
          readRecord(lsn);
          logRecord.setLSN(readLSN);
          readLSN += logRecord.getLogSize();
          return logRecord;
      }
  
      private void readRecord(long lsn) {
          ByteBuffer buffer = this.readBuffer;
          while (true) {
              RecordReadStatus status = logRecord.readLogRecord(buffer);
              switch (status) {
                  case LARGE_RECORD:
                      buffer = ByteBuffer.allocate(logRecord.getLogSize());
                      fillLogReadBuffer(logRecord.getLogSize(), buffer);
                      //now see what we have in the refilled buffer
                      break;
                  case TRUNCATED:
                      if (!fillLogReadBuffer()) {
                          throw new IllegalStateException(
                                  "Could not read LSN(" + lsn + ") from log file id " + logFile.getLogFileId());
                      }
                      //now read the complete log record
                      break;
                  case BAD_CHKSUM:
                      throw new ACIDException("Log record has incorrect checksum");
                  case OK:
                      return;
                  default:
                      throw new IllegalStateException("Unexpected log read status: " + status);
              }
          }
      }
  
      private void getLogFile() {
          try {
              // close existing file (if any) before opening another one
              close();
              logFile = logMgr.getLogFile(readLSN);
              fileBeginLSN = logFile.getFileBeginLSN();
          } catch (IOException e) {
              throw new ACIDException(e);
          }
      }
  
      @Override
      public void close() {
          try {
              if (logFile != null) {
                  logFile.close();
                  logFile = null;
              }
          } catch (IOException e) {
              throw new ACIDException(e);
          }
      }
  }
  