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.cassandra.journal;
  
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.nio.MappedByteBuffer;
  import java.nio.channels.FileChannel;
  import java.nio.file.StandardOpenOption;
  import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
  import java.util.concurrent.atomic.AtomicLongFieldUpdater;
  import java.util.concurrent.locks.LockSupport;
  import java.util.function.Consumer;
  
  import accord.utils.Invariants;
  import com.codahale.metrics.Timer;
  import com.google.common.annotations.VisibleForTesting;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import org.apache.cassandra.db.TypeSizes;
  import org.apache.cassandra.utils.*;
  import org.apache.cassandra.utils.concurrent.OpOrder;
  import org.apache.cassandra.utils.concurrent.Ref;
  import org.apache.cassandra.utils.concurrent.WaitQueue;
  import org.apache.cassandra.utils.memory.MemoryUtil;
  
  import static org.apache.cassandra.utils.Simulate.With.MONITORS;
  
  @Simulate(with=MONITORS)
  public final class ActiveSegment<K, V> extends Segment<K, V>
  {
      private static final Logger logger = LoggerFactory.getLogger(ActiveSegment.class);
  
      final FileChannel channel;
  
      // OpOrder used to order appends wrt flush
      private final OpOrder appendOrder = new OpOrder();
  
      // position in the buffer we are allocating from
      private volatile long allocateOffset = 0;
      private static final AtomicLongFieldUpdater<ActiveSegment> allocateOffsetUpdater = AtomicLongFieldUpdater.newUpdater(ActiveSegment.class, "allocateOffset");
  
      /*
       * Everything before this offset has been written and flushed.
       */
      private volatile int writtenTo = 0;
      private volatile int fsyncedTo = 0;
      @SuppressWarnings("rawtypes")
      private static final AtomicIntegerFieldUpdater<ActiveSegment> writtenToUpdater = AtomicIntegerFieldUpdater.newUpdater(ActiveSegment.class, "writtenTo");
      @SuppressWarnings("rawtypes")
      private static final AtomicIntegerFieldUpdater<ActiveSegment> fsyncedToUpdater = AtomicIntegerFieldUpdater.newUpdater(ActiveSegment.class, "fsyncedTo");
  
      /*
       * End position of the buffer; initially set to its capacity and
       * updated to point to the last written position as the segment is being closed
       * no need to be volatile as writes are protected by appendOrder barrier.
       */
      private int endOfBuffer;
  
      // a signal that writers can wait on to be notified of a completed flush in BATCH and GROUP FlushMode
      private final WaitQueue flushComplete = WaitQueue.newWaitQueue();
  
      private final Ref<Segment<K, V>> selfRef;
  
      final InMemoryIndex<K> index;
  
      private ActiveSegment(
          Descriptor descriptor, Params params, InMemoryIndex<K> index, Metadata metadata, KeySupport<K> keySupport)
      {
          super(descriptor, metadata, keySupport);
          this.index = index;
          try
          {
              channel = FileChannel.open(file.toPath(), StandardOpenOption.WRITE, StandardOpenOption.READ, StandardOpenOption.CREATE);
              buffer = channel.map(FileChannel.MapMode.READ_WRITE, 0, params.segmentSize());
              endOfBuffer = buffer.capacity();
              selfRef = new Ref<>(this, new Tidier(descriptor, channel, buffer));
          }
          catch (IOException e)
          {
              throw new JournalWriteError(descriptor, file, e);
          }
      }
  
      static <K, V> ActiveSegment<K, V> create(Descriptor descriptor, Params params, KeySupport<K> keySupport)
      {
          InMemoryIndex<K> index = InMemoryIndex.create(keySupport);
          Metadata metadata = Metadata.empty();
          return new ActiveSegment<>(descriptor, params, index, metadata, keySupport);
      }
  
      @Override
      public InMemoryIndex<K> index()
      {
          return index;
      }
  
      boolean isEmpty()
      {
          return allocateOffset == 0;
      }
  
      @Override
      boolean isActive()
      {
          return true;
      }
  
      @Override
      ActiveSegment<K, V> asActive()
      {
          return this;
      }
  
      @Override
      StaticSegment<K, V> asStatic()
      {
          throw new UnsupportedOperationException();
      }
  
      /**
       * Read the entry and specified offset into the entry holder.
       * Expects the caller to acquire the ref to the segment and the record to exist.
       */
      @Override
      boolean read(int offset, int size, EntrySerializer.EntryHolder<K> into)
      {
          ByteBuffer duplicate = buffer.duplicate().position(offset).limit(offset + size);
          try
          {
              EntrySerializer.read(into, keySupport, duplicate, descriptor.userVersion);
          }
          catch (IOException e)
          {
              throw new JournalReadError(descriptor, file, e);
          }
          return true;
      }
  
      /**
       * Stop writing to this file, flush and close it. Does nothing if the file is already closed.
       */
      public synchronized void close(Journal<K, V> journal)
      {
          close(journal, true);
      }
  
      /**
       * @return true if the closed segment was definitely empty, false otherwise
       */
      private synchronized boolean close(Journal<K, V> journal, boolean persistComponents)
      {
          boolean isEmpty = discardUnusedTail();
          if (!isEmpty)
          {
              updateWrittenTo();
              fsync();
              if (persistComponents) persistComponents();
          }
          release(journal);
          return isEmpty;
      }
  
      /**
       * Close and discard a pre-allocated, available segment, that's never been exposed
       */
      void closeAndDiscard(Journal<K, V> journal)
      {
          boolean isEmpty = close(journal, false);
          if (!isEmpty) throw new IllegalStateException();
          discard();
      }
  
      void closeAndIfEmptyDiscard(Journal<K, V> journal)
      {
          boolean isEmpty = close(journal, true);
          if (isEmpty) discard();
      }
  
      void persistComponents()
      {
          index.persist(descriptor);
          metadata.persist(descriptor);
          SyncUtil.trySyncDir(descriptor.directory);
      }
  
      private void discard()
      {
          logger.debug("Discarding {}", this);
          selfRef.ensureReleased();
  
          descriptor.fileFor(Component.DATA).deleteIfExists();
          descriptor.fileFor(Component.INDEX).deleteIfExists();
          descriptor.fileFor(Component.METADATA).deleteIfExists();
      }
  
      @Override
      public Ref<Segment<K, V>> tryRef()
      {
          return selfRef.tryRef();
      }
  
      @Override
      public Ref<Segment<K, V>> ref()
      {
          return selfRef.ref();
      }
  
      @Override
      public Ref<Segment<K, V>> selfRef()
      {
          return selfRef;
      }
  
      private static final class Tidier extends Segment.Tidier implements Tidy
      {
          private final Descriptor descriptor;
          private final FileChannel channel;
          private final ByteBuffer buffer;
  
          Tidier(Descriptor descriptor, FileChannel channel, ByteBuffer buffer)
          {
              this.descriptor = descriptor;
              this.channel = channel;
              this.buffer = buffer;
          }
  
          @Override
          void onUnreferenced()
          {
              MemoryUtil.clean(buffer);
              try
              {
                  channel.close();
              }
              catch (IOException e)
              {
                  throw new JournalWriteError(descriptor, Component.DATA, e);
              }
          }
  
          @Override
          public String name()
          {
              return descriptor.toString();
          }
      }
  
      public boolean isFlushed(long position)
      {
          return writtenTo >= position;
      }
  
      public int writtenToAtLeast()
      {
          return writtenTo;
      }
  
      public int fsyncedTo()
      {
          return fsyncedTo;
      }
  
      public int updateWrittenTo()
      {
          int allocatedTo = (int)allocateOffset;
          if (writtenTo >= allocatedTo)
              return writtenTo;
  
          waitForModifications();
          return writtenToUpdater.accumulateAndGet(this, allocatedTo, Math::max);
      }
  
      // provides no ordering guarantees
      void fsync()
      {
          int writtenTo = this.writtenTo;
          if (fsyncedTo >= writtenTo)
              return;
  
          fsyncInternal();
          fsyncedToUpdater.accumulateAndGet(this, writtenTo, Math::max);
          flushComplete.signalAll();
      }
  
      private void waitForFlush(int position)
      {
          while (fsyncedTo < position)
          {
              WaitQueue.Signal signal = flushComplete.register();
              if (fsyncedTo < position)
                  signal.awaitThrowUncheckedOnInterrupt();
              else
                  signal.cancel();
          }
      }
  
      /**
       * Wait for any appends or discardUnusedTail() operations started before this method was called
       */
      private void waitForModifications()
      {
          // issue a barrier and wait for it
          appendOrder.awaitNewBarrier();
      }
  
      private void fsyncInternal()
      {
          try
          {
              SyncUtil.force((MappedByteBuffer) buffer);
          }
          catch (Exception e) // MappedByteBuffer.force() does not declare IOException but can actually throw it
          {
              throw new JournalWriteError(descriptor, file, e);
          }
      }
  
      /**
       * Ensures no more of this segment is writeable, by allocating any unused section at the end
       * and marking it discarded void discartUnusedTail()
       *
       * @return true if the segment was empty, false otherwise
       */
      boolean discardUnusedTail()
      {
          try (OpOrder.Group ignored = appendOrder.start())
          {
              while (true)
              {
                  long prev = completeInProgress();
                  int next = endOfBuffer + 1;
  
                  if ((int)prev >= next)
                  {
                      // already stopped allocating, might also be closed
                      Invariants.require(buffer == null || prev == buffer.capacity() + 1);
                      return false;
                  }
  
                  if (allocateOffsetUpdater.compareAndSet(this, prev, next))
                  {
                      // stopped allocating now; can only succeed once, no further allocation or discardUnusedTail can succeed
                      endOfBuffer = (int)prev;
                      assert buffer != null && next == buffer.capacity() + 1;
                      metadata.fsyncLimit((int) prev);
                      return prev == 0;
                  }
                  LockSupport.parkNanos(1);
              }
          }
      }
  
      /*
       * Entry/bytes allocation logic
       */
  
      @SuppressWarnings({ "resource", "RedundantSuppression" }) // op group will be closed by Allocation#write()
      Allocation allocate(int entrySize)
      {
          int totalSize = totalEntrySize(entrySize);
          OpOrder.Group opGroup = appendOrder.start();
          try
          {
              int position = allocateBytes(totalSize);
              if (position < 0)
              {
                  opGroup.close();
                  return null;
              }
              return new Allocation(opGroup, buffer.duplicate().position(position).limit(position + totalSize), totalSize);
          }
          catch (Throwable t)
          {
              opGroup.close();
              throw t;
          }
      }
  
      private int totalEntrySize(int recordSize)
      {
          return EntrySerializer.headerSize(keySupport, descriptor.userVersion)
               + recordSize
               + TypeSizes.INT_SIZE // CRC
          ;
      }
  
      // allocate bytes in the segment, or return -1 if not enough space
      private int allocateBytes(int size)
      {
          while (true)
          {
              long prev = maybeCompleteInProgress();
              if (prev < 0)
              {
                  LockSupport.parkNanos(1); // ConstantBackoffCAS Algorithm from https://arxiv.org/pdf/1305.5800.pdf
                  continue;
              }
  
              long next = prev + size;
              if (next >= endOfBuffer)
                  return -1;
  
              // TODO (expected): if we write a "safe shutdown" marker we don't need this,
              //  but this provides safe restart in the event the process terminates abruptly but the host remains stable
              long inProgress = prev | (next << 32);
              if (!allocateOffsetUpdater.compareAndSet(this, prev, inProgress))
              {
                  LockSupport.parkNanos(1); // ConstantBackoffCAS Algorithm from https://arxiv.org/pdf/1305.5800.pdf
                  continue;
              }
  
              assert buffer != null;
              buffer.putInt((int)prev, (int)next);
              allocateOffsetUpdater.compareAndSet(this, inProgress, next);
              return (int) prev;
          }
      }
  
      final class Allocation
      {
          private final OpOrder.Group appendOp;
          private final ByteBuffer buffer;
          private final int start;
          private final int length;
  
          Allocation(OpOrder.Group appendOp, ByteBuffer buffer, int length)
          {
              this.appendOp = appendOp;
              this.buffer = buffer;
              this.start = buffer.position();
              this.length = length;
          }
  
          void write(K id, ByteBuffer record)
          {
              try
              {
                  EntrySerializer.write(id, record, keySupport, buffer, descriptor.userVersion);
                  metadata.update();
                  index.update(id, start, length);
              }
              catch (IOException e)
              {
                  throw new JournalWriteError(descriptor, file, e);
              }
              finally
              {
                  appendOp.close();
              }
          }
  
          // TODO (required): Find a better way to test unwritten allocations and/or corruption
          @VisibleForTesting
          void consumeBufferUnsafe(Consumer<ByteBuffer> fn)
          {
              try
              {
                  fn.accept(buffer);
              }
              finally
              {
                  appendOp.close();
              }
          }
  
  
          // Variant of write that does not allocate/return a record pointer
          void writeInternal(K id, ByteBuffer record)
          {
              try
              {
                  EntrySerializer.write(id, record, keySupport, buffer, descriptor.userVersion);
                  index.update(id, start, length);
                  metadata.update();
              }
              catch (IOException e)
              {
                  throw new JournalWriteError(descriptor, file, e);
              }
              finally
              {
                  appendOp.close();
              }
          }
  
          void awaitDurable(Timer waitingOnFlush)
          {
              try (Timer.Context ignored = waitingOnFlush.time())
              {
                  waitForFlush(start);
              }
          }
  
          boolean isFsynced()
          {
              return fsyncedTo >= start + length;
          }
  
          Descriptor descriptor()
          {
              return descriptor;
          }
  
          int start()
          {
              return start;
          }
      }
  
      private int maybeCompleteInProgress()
      {
          long cur = allocateOffset;
          int inProgress = (int) (cur >>> 32);
          if (inProgress == 0) return (int) cur;
          // finish up the in-progress allocation
          buffer.putInt((int)cur, inProgress);
          if (!allocateOffsetUpdater.compareAndSet(this, cur, inProgress))
              return -1;
  
          return inProgress;
      }
  
      private int completeInProgress()
      {
          int result = maybeCompleteInProgress();
          while (result < 0)
              result = maybeCompleteInProgress();
          return result;
      }
  }
  