/**
* 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.hadoop.hbase.regionserver.wal;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.htrace.Span;
/**
* A Future on a filesystem sync call. It given to a client or 'Handler' for it to wait on till
* the sync completes.
*
* <p>Handlers coming in call append, append, append, and then do a flush/sync of
* the edits they have appended the WAL before returning. Since sync takes a while to
* complete, we give the Handlers back this sync future to wait on until the
* actual HDFS sync completes. Meantime this sync future goes across the ringbuffer and into a
* sync runner thread; when it completes, it finishes up the future, the handler get or failed
* check completes and the Handler can then progress.
* <p>
* This is just a partial implementation of Future; we just implement get and
* failure. Unimplemented methods throw {@link UnsupportedOperationException}.
* <p>
* There is not a one-to-one correlation between dfs sync invocations and
* instances of this class. A single dfs sync call may complete and mark many
* SyncFutures as done; i.e. we batch up sync calls rather than do a dfs sync
* call every time a Handler asks for it.
* <p>
* SyncFutures are immutable but recycled. Call {@link #reset(long, Span)} before use even
* if it the first time, start the sync, then park the 'hitched' thread on a call to
* {@link #get()}
*/
@InterfaceAudience.Private
class SyncFuture {
// Implementation notes: I tried using a cyclicbarrier in here for handler and sync threads
// to coordinate on but it did not give any obvious advantage and some issues with order in which
// events happen.
private static final long NOT_DONE = 0;
/**
* The sequence at which we were added to the ring buffer.
*/
private long ringBufferSequence;
/**
* The sequence that was set in here when we were marked done. Should be equal
* or > ringBufferSequence. Put this data member into the NOT_DONE state while this
* class is in use. But for the first position on construction, let it be -1 so we can
* immediately call {@link #reset(long, Span)} below and it will work.
*/
private long doneSequence = -1;
/**
* If error, the associated throwable. Set when the future is 'done'.
*/
private Throwable throwable = null;
private Thread t;
/**
* Optionally carry a disconnected scope to the SyncRunner.
*/
private Span span;
/**
* Call this method to clear old usage and get it ready for new deploy. Call
* this method even if it is being used for the first time.
*
* @param sequence sequenceId from this Future's position in the RingBuffer
* @return this
*/
synchronized SyncFuture reset(final long sequence) {
return reset(sequence, null);
}
/**
* Call this method to clear old usage and get it ready for new deploy. Call
* this method even if it is being used for the first time.
*
* @param sequence sequenceId from this Future's position in the RingBuffer
* @param span curren span, detached from caller. Don't forget to attach it when
* resuming after a call to {@link #get()}.
* @return this
*/
synchronized SyncFuture reset(final long sequence, Span span) {
if (t != null && t != Thread.currentThread()) throw new IllegalStateException();
t = Thread.currentThread();
if (!isDone()) throw new IllegalStateException("" + sequence + " " + Thread.currentThread());
this.doneSequence = NOT_DONE;
this.ringBufferSequence = sequence;
this.span = span;
return this;
}
@Override
public synchronized String toString() {
return "done=" + isDone() + ", ringBufferSequence=" + this.ringBufferSequence;
}
synchronized long getRingBufferSequence() {
return this.ringBufferSequence;
}
/**
* Retrieve the {@code span} instance from this Future. EventHandler calls
* this method to continue the span. Thread waiting on this Future musn't call
* this method until AFTER calling {@link #get()} and the future has been
* released back to the originating thread.
*/
synchronized Span getSpan() {
return this.span;
}
/**
* Used to re-attach a {@code span} to the Future. Called by the EventHandler
* after a it has completed processing and detached the span from its scope.
*/
synchronized void setSpan(Span span) {
this.span = span;
}
/**
* @param sequence Sync sequence at which this future 'completed'.
* @param t Can be null. Set if we are 'completing' on error (and this 't' is the error).
* @return True if we successfully marked this outstanding future as completed/done.
* Returns false if this future is already 'done' when this method called.
*/
synchronized boolean done(final long sequence, final Throwable t) {
if (isDone()) return false;
this.throwable = t;
if (sequence < this.ringBufferSequence) {
// Something badly wrong.
if (throwable == null) {
this.throwable = new IllegalStateException("sequence=" + sequence +
", ringBufferSequence=" + this.ringBufferSequence);
}
}
// Mark done.
this.doneSequence = sequence;
// Wake up waiting threads.
notify();
return true;
}
public boolean cancel(boolean mayInterruptIfRunning) {
throw new UnsupportedOperationException();
}
public synchronized long get() throws InterruptedException, ExecutionException {
while (!isDone()) {
wait(1000);
}
if (this.throwable != null) throw new ExecutionException(this.throwable);
return this.doneSequence;
}
public Long get(long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException {
throw new UnsupportedOperationException();
}
public boolean isCancelled() {
throw new UnsupportedOperationException();
}
synchronized boolean isDone() {
return this.doneSequence != NOT_DONE;
}
synchronized boolean isThrowable() {
return isDone() && getThrowable() != null;
}
synchronized Throwable getThrowable() {
return this.throwable;
}
}