Non blocking ReservedThreadExecutor #6535
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Never block waiting for reserved thread. Dump reserved thread stack if it does not make the rendezvous
…95-ReservedThreadExecutor
fix warnings
Signed-off-by: Simone Bordet <simone.bordet@gmail.com>
Signed-off-by: Simone Bordet <simone.bordet@gmail.com>
Signed-off-by: Simone Bordet <simone.bordet@gmail.com>
Signed-off-by: Simone Bordet <simone.bordet@gmail.com>
avoid waiting 1s
If a reserved thread does not rendezvous, put it back on the bottom of the stack.
Even more paranoid checks: + test if an missed offer was for a thread that removed itself from the stack + test if a reserved thread is already on the stack before adding it.
Even more paranoid checks: + try to poll after remove to check for race in remove
Even more paranoid checks: + try to poll after remove to check for race in remove
This is a new approach to #6495. A call to offer must never block, nor even yield, since to do so give an opportunity for the allocated CPU core to change, defeating the whole purpose of the class. There is also some reasonable level of diagnostic warnings if a reserved thread misses too many offers consecutively, based on tracking the state of the reserved thread.
Use MAX_VALUE rather than -1 as the stopped marker value.
Remove the stack data structure entirely. ReservedThreads all poll the same SynchronousQueue and tryExecute does a non blocking offer.
Added test for busy shrinking
Remember last time we hit zero reserved threads
lorban
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Jul 23, 2021
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Signed-off-by: Greg Wilkins <gregw@webtide.com>
Signed-off-by: Greg Wilkins <gregw@webtide.com>
…:eclipse/jetty.project into jetty-9.4.x-6495-ReservedThreadExecutor3
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simplified tryExecute
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A call to offer must never block, nor even yield, since to do so give an opportunity for the allocated CPU core to change, defeating the whole purpose of the class. There is also some reasonable level of diagnostic warnings if a reserved thread misses too many offers consecutively, based on tracking the state of the reserved thread. Remove the stack data structure entirely. ReservedThreads all poll the same SynchronousQueue and tryExecute does a non blocking offer. Added test for busy shrinking Remember last time we hit zero reserved threads Co-authored-by: Simone Bordet <simone.bordet@gmail.com>
gregw
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A call to offer must never block, nor even yield, since to do so give an opportunity for the allocated CPU core to change, defeating the whole purpose of the class. There is also some reasonable level of diagnostic warnings if a reserved thread misses too many offers consecutively, based on tracking the state of the reserved thread. Remove the stack data structure entirely. ReservedThreads all poll the same SynchronousQueue and tryExecute does a non blocking offer. Added test for busy shrinking Remember last time we hit zero reserved threads Co-authored-by: Simone Bordet <simone.bordet@gmail.com>
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This is yet another alternative fix for #6495 replacing #6496
The stack is removed entirely and all the reserved threads poll in parallel on the same synchronous queue.
The
tryExecutesemantic is simply to do a non-blocking offer to the queue which will either succeed or fail, and no further action is required.The
sizeandpendingcounts are important to keep the capacity correct.The reserved threads are added as beans, but only for the purposes of dumping.
The reserved threads track their state to make the dumps more meaningful.
The only issue with losing the stack is that it may prevent reserved threads idling out as load might be shared over all the reserved threads rather than just the most recent.
However, there are other strategies that could be applied to deal with that (eg looking at recent minimum size before re-polling).