[SOLR-16165] Deadlock in SlotAcc initialization

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 9.0, 8.11.1, 9.1
• Fix Version/s: 9.1.1
• Component/s: faceting
• Assignee: Noble Paul
• Reporter: Justin Sweeney
• Created: 24/Apr/22 17:02
• Updated: 16/Oct/23 06:39
• Resolved: 30/Nov/22 05:57

Description

The core of the issue is that if a parent class reference an instance of its own child class as a static field, a deadlock can be created if 1 thread tries to access the parent class and another thread to the child class.

Thread A

"qtp1393828949-98" #98 prio=5 os_prio=0 cpu=294.10ms elapsed=6252.75s allocated=53246K defined_classes=243 tid=0x00007fa47c007000 nid=0x349c4e in Object.wait() [0x00007f9896620000]
java.lang.Thread.State: RUNNABLE
at org.apache.solr.search.facet.SlotAcc.<clinit>(SlotAcc.java:830)
at org.apache.solr.search.facet.FacetFieldProcessorByHashDV.createCollectAcc(FacetFieldProcessorByHashDV.java:271)
at org.apache.solr.search.facet.FacetFieldProcessorByHashDV.calcFacets(FacetFieldProcessorByHashDV.java:255)

Thread B

"qtp1393828949-2379" #2379 prio=5 os_prio=0 cpu=34.52ms elapsed=6013.46s allocated=20426K defined_classes=0 tid=0x00007fa49c081800 nid=0x34a58b in Object.wait() [0x00007f5fcfae7000]
java.lang.Thread.State: RUNNABLE
at org.apache.solr.search.facet.FacetFieldProcessorByArray.createCollectAcc(FacetFieldProcessorByArray.java:85)
at org.apache.solr.search.facet.FacetFieldProcessorByArray.calcFacets(FacetFieldProcessorByArray.java:144)
at org.apache.solr.search.facet.FacetFieldProcessorByArray.process(FacetFieldProcessorByArray.java:94)
... # Thread A : FacetFieldProcessorByHashDV.java:271 indexOrderAcc = new SlotAcc(fcontext) {, which accesses class SlotAcc, it would have a class init lock on SlotAcc(assuming first time loading SlotAcc in classloader) but BEFORE run to line SlotAcc.java:830

1. Thread B: FacetFieldProcessorByArray.java:85 countAcc = new SweepingCountSlotAcc(numSlots, this);. Accesses SweepingCountSlotAcc (also assuming first time loading SweepingCountSlotAcc in classloader), loads and initialize based on hierarchy SweepingCountSlotAcc > CountSlotArrAcc > CountSlotAcc -> SlotAcc, obtain lock and initialize SweepingCountSlotAcc,CountSlotArrAcc,CountSlotAcc but blocked on loading/initializing parent class SlotAcc, since Thread A has lock and is already initializing it
2. Thread A: run to line 830 static final CountSlotAcc DEV_NULL_SLOT_ACC = new CountSlotAcc(null)... Found CountSlotAcc, it will attempt to load CountSlotAcc as well, but such lock is held by Thread B

Issue Links

• relates to: SOLR-16167 Review static initializers that reference subclasses
• links to: GitHub Pull Request #819