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Issue #4096 resolve race between doStop and adding new threads to stack 

Now using the _size AtomicInteger to resolve the race between stopping
and adding to the stack.

A _size of -1 now means no more threads can be added to the stack, and
the loop in doStop() will now only exit if it can set the size to -1.

Signed-off-by: Lachlan Roberts <lachlan@webtide.com>
This commit is contained in:
Lachlan Roberts 2019-09-23 11:56:25 +10:00
parent 168a95d334
commit ac93ff6272
1 changed files with 30 additions and 11 deletions
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41
jetty-util/src/main/java/org/eclipse/jetty/util/thread/ReservedThreadExecutor.java
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@ -155,6 +155,7 @@ public class ReservedThreadExecutor extends AbstractLifeCycle implements TryExec
public void doStart() throws Exception
{
_lease = ThreadPoolBudget.leaseFrom(getExecutor(), this, _capacity);
_size.set(0);
super.doStart();
}
@ -168,9 +169,21 @@ public class ReservedThreadExecutor extends AbstractLifeCycle implements TryExec
while (true)
{
int size = _size.get();
// If no reserved threads left try setting size to -1 to
// atomically prevent other threads adding themselves to stack.
if (size == 0 && _size.compareAndSet(size, -1))
break;
ReservedThread thread = _stack.pollFirst();
if (thread == null)
break;
{
// Reserved thread must have incremented size but not yet added itself to queue.
// We will spin until it is added.
Thread.yield(); // TODO: use Thread.onSpinWait() in jetty-10
continue;
}
_size.decrementAndGet();
thread.stop();
}
@ -278,11 +291,12 @@ public class ReservedThreadExecutor extends AbstractLifeCycle implements TryExec
if (LOG.isDebugEnabled())
LOG.debug("{} waiting", this);
Runnable task = null;
while (isRunning() && task == null)
while (true)
{
boolean idle = false;
if (!isRunning())
return STOP;
boolean idle = false;
try (Locker.Lock lock = _locker.lock())
{
if (_task == null)
@ -299,8 +313,16 @@ public class ReservedThreadExecutor extends AbstractLifeCycle implements TryExec
LOG.ignore(e);
}
}
task = _task;
_task = null;
else
{
Runnable task = _task;
_task = null;
if (LOG.isDebugEnabled())
LOG.debug("{} task={}", this, task);
return task;
}
}
if (idle)
@ -315,11 +337,6 @@ public class ReservedThreadExecutor extends AbstractLifeCycle implements TryExec
tryExecute(STOP);
}
}
if (LOG.isDebugEnabled())
LOG.debug("{} task={}", this, task);
return task;
}
@Override
@ -332,6 +349,8 @@ public class ReservedThreadExecutor extends AbstractLifeCycle implements TryExec
while (true)
{
int size = _size.get();
if (size < 0)
return;
if (size >= _capacity)
{
if (LOG.isDebugEnabled())