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Issue #1924 - ManagedSelector livelock. (#1963) 

* Issue #1924 - ManagedSelector livelock.

Alternate implementation that is count based rather than time based.

Signed-off-by: Greg Wilkins <gregw@webtide.com>
This commit is contained in:
Greg Wilkins 2017-11-14 10:27:04 +01:00 committed by GitHub
parent 48df74224a
commit 47d46ec60e
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1 changed files with 33 additions and 25 deletions
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58
jetty-io/src/main/java/org/eclipse/jetty/io/ManagedSelector.java
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@ -58,7 +58,6 @@ import org.eclipse.jetty.util.thread.strategy.EatWhatYouKill;
public class ManagedSelector extends ContainerLifeCycle implements Dumpable
{
private static final Logger LOG = Log.getLogger(ManagedSelector.class);
private static final long MAX_ACTION_PERIOD_MS = Long.getLong("org.eclipse.jetty.io.ManagedSelector.MAX_ACTION_PERIOD_MS",100);
private final Locker _locker = new Locker();
private boolean _selecting = false;
@ -67,7 +66,7 @@ public class ManagedSelector extends ContainerLifeCycle implements Dumpable
private final int _id;
private final ExecutionStrategy _strategy;
private Selector _selector;
private long _actionTime = -1;
private int _actionCount;
public ManagedSelector(SelectorManager selectorManager, int id)
{
@ -304,7 +303,6 @@ public class ManagedSelector extends ContainerLifeCycle implements Dumpable
private Runnable nextAction()
{
long now = System.nanoTime();
Selector selector = null;
Runnable action = null;
try (Locker.Lock lock = _locker.lock())
@ -312,38 +310,48 @@ public class ManagedSelector extends ContainerLifeCycle implements Dumpable
// It is important to avoid live-lock (busy blocking) here. If too many actions
// are submitted, this can indefinitely defer selection happening. Similarly if
// we give too much priority to selection, it may prevent actions from being run.
// The solution implemented here is to put a maximum time limit on handling actions
// so that this method will fall through to selection if more than MAX_ACTION_PERIOD_MS
// is spent running actions. The time period is cleared whenever a selection occurs,
// so that a full period can be spent on actions after every select.
if (_actionTime == -1)
{
_actionTime = now;
// The solution implemented here is to only process the number of actions that were
// originally in the action queue before attempting a select
if (_actionCount==0)
{
// Calculate how many actions we are prepared to handle before selection
_actionCount = _actions.size();
if (_actionCount>0)
action = _actions.poll();
else
_selecting = true;
}
else if ((now - _actionTime) > TimeUnit.MILLISECONDS.toNanos(MAX_ACTION_PERIOD_MS) && _actions.size() > 0)
else if (_actionCount==1)
{
// Too much time spent handling actions, give selection a go,
// immediately waking up (as if remaining action were just added).
selector = _selector;
_selecting = false;
_actionTime = -1;
_actionCount = 0;
if (LOG.isDebugEnabled())
LOG.debug("Forcing selection, actions={}",_actions.size());
}
if (selector == null)
{
action = _actions.poll();
if (action == null)
if (_actions.size()==0)
{
// No more actions, so we time to do some selecting
// This was the last action, so select normally
_selecting = true;
_actionTime = -1;
}
else
{
// there are still more actions to handle, so
// immediately wake up (as if remaining action were just added).
selector = _selector;
_selecting = false;
}
}
else
{
_actionCount--;
action = _actions.poll();
}
}
if (LOG.isDebugEnabled())
LOG.debug("action={} wakeup={}",action,selector!=null);
if (selector != null)
selector.wakeup();