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/**
* 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.hadoop.hbase.exceptions.TimeoutIOException;
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.
*
* 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 a queue and is handled by a background thread; when it completes, it finishes up the
* future, the handler get or failed check completes and the Handler can then progress.
*
* This is just a partial implementation of Future; we just implement get and failure.
*
* 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.
*
* SyncFutures are immutable but recycled. Call #reset(long, Span) before use even if it the first
* time, start the sync, then park the 'hitched' thread on a call to #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 = -1L;
/**
* The transaction id of this operation, monotonically increases.
*/
private long txid;
/**
* The transaction id that was set in here when we were marked done. Should be equal or > txnId.
* Put this data member into the NOT_DONE state while this class is in use.
*/
private long doneTxid;
/**
* If error, the associated throwable. Set when the future is 'done'.
*/
private Throwable throwable;
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.
* @param txid the new transaction id
* @param span current span, detached from caller. Don't forget to attach it when resuming after a
* call to {@link #get(long)}.
* @return this
*/
synchronized SyncFuture reset(final long txid, Span span) {
if (t != null && t != Thread.currentThread()) {
throw new IllegalStateException();
}
t = Thread.currentThread();
if (!isDone()) {
throw new IllegalStateException("" + txid + " " + Thread.currentThread());
}
this.doneTxid = NOT_DONE;
this.txid = txid;
this.span = span;
this.throwable = null;
return this;
}
@Override
public synchronized String toString() {
return "done=" + isDone() + ", txid=" + this.txid;
}
synchronized long getTxid() {
return this.txid;
}
/**
* 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(long)} 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 txid the transaction id 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 txid, final Throwable t) {
if (isDone()) {
return false;
}
this.throwable = t;
if (txid < this.txid) {
// Something badly wrong.
if (throwable == null) {
this.throwable =
new IllegalStateException("done txid=" + txid + ", my txid=" + this.txid);
}
}
// Mark done.
this.doneTxid = txid;
// Wake up waiting threads.
notify();
return true;
}
boolean cancel(boolean mayInterruptIfRunning) {
throw new UnsupportedOperationException();
}
synchronized long get(long timeoutNs) throws InterruptedException,
ExecutionException, TimeoutIOException {
final long done = System.nanoTime() + timeoutNs;
while (!isDone()) {
wait(1000);
if (System.nanoTime() >= done) {
throw new TimeoutIOException(
"Failed to get sync result after " + TimeUnit.NANOSECONDS.toMillis(timeoutNs)
+ " ms for txid=" + this.txid + ", WAL system stuck?");
}
}
if (this.throwable != null) {
throw new ExecutionException(this.throwable);
}
return this.doneTxid;
}
synchronized boolean isDone() {
return this.doneTxid != NOT_DONE;
}
synchronized boolean isThrowable() {
return isDone() && getThrowable() != null;
}
synchronized Throwable getThrowable() {
return this.throwable;
}
}