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Parallel backend can deadlock when accessing the synchronizing access to frontend. #19293

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WojciechMazur opened this issue Dec 18, 2023 · 0 comments · Fixed by #19298
Closed

Parallel backend can deadlock when accessing the synchronizing access to frontend. #19293

WojciechMazur opened this issue Dec 18, 2023 · 0 comments · Fixed by #19298
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area:backend itype:bug

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WojciechMazur commented Dec 18, 2023 •
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When fixed the PR disabled parallel backend tests should be reverted: #19292

Compiler version

Scala 3.4.0-RC1.nightly
Can exist in all 3.4.x versions after merge of #15392

Minimized code

Not yet minimized,
Threads seem to deadlock when accessing the lazy variable which is initialized in the synchronized scope

https://github.com/lampepfl/dotty/blob/e4985fc7d9de349fe3b43ddb06c8369d795c847d/compiler/src/dotty/tools/backend/jvm/CoreBTypes.scala#L170-L178

Where frontendSynch is defined as
https://github.com/lampepfl/dotty/blob/e4985fc7d9de349fe3b43ddb06c8369d795c847d/compiler/src/dotty/tools/backend/jvm/PostProcessorFrontendAccess.scala#L27-L28

Thread 1 dump:

"ForkJoinPool-1-worker-2" #22 daemon prio=5 os_prio=31 cpu=4170.43ms elapsed=1210.47s tid=0x00000001370f8200 nid=0x9f03 waiting on condition  [0x0000000173d5d000]
   java.lang.Thread.State: WAITING (parking)
        at jdk.internal.misc.Unsafe.park(java.base@17.0.7/Native Method)
        - parking to wait for  <0x0000000608a64ff8> (a java.util.concurrent.CountDownLatch$Sync)
        at java.util.concurrent.locks.LockSupport.park(java.base@17.0.7/LockSupport.java:211)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(java.base@17.0.7/AbstractQueuedSynchronizer.java:715)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(java.base@17.0.7/AbstractQueuedSynchronizer.java:1047)
        at java.util.concurrent.CountDownLatch.await(java.base@17.0.7/CountDownLatch.java:230)
        at dotty.tools.backend.jvm.CoreBTypesFromSymbols.jliLambdaMetaFactoryAltMetafactoryHandle$lzyINIT1(CoreBTypes.scala:178)
        at dotty.tools.backend.jvm.CoreBTypesFromSymbols.jliLambdaMetaFactoryAltMetafactoryHandle(CoreBTypes.scala:170)
        at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genInvokeDynamicLambda(BCodeBodyBuilder.scala:1823)
        at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadTo(BCodeBodyBuilder.scala:383)
        at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadTo(BCodeBodyBuilder.scala:456)
        at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:304)
        at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.loop$1(BCodeBodyBuilder.scala:1210)
        at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadArguments(BCodeBodyBuilder.scala:1217)
        at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genApply(BCodeBodyBuilder.scala:836)
        at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadTo(BCodeBodyBuilder.scala:386)
        at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:304)
        at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genStat(BCodeBodyBuilder.scala:116)
        at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genBlockTo$$anonfun$1(BCodeBodyBuilder.scala:1094)
        at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder$$Lambda$2749/0x00000008007a1b98.applyVoid(Unknown Source)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genBlockTo(BCodeBodyBuilder.scala:1094)
        at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadTo(BCodeBodyBuilder.scala:458)
        at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.emitNormalMethodBody$1(BCodeSkelBuilder.scala:893)
        at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.genDefDef(BCodeSkelBuilder.scala:916)
        at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.gen(BCodeSkelBuilder.scala:693)
        at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.gen$$anonfun$1(BCodeSkelBuilder.scala:699)
        at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder$$Lambda$2735/0x0000000800799380.applyVoid(Unknown Source)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.gen(BCodeSkelBuilder.scala:699)
        at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.genPlainClass(BCodeSkelBuilder.scala:293)
        at dotty.tools.backend.jvm.CodeGen.genClass(CodeGen.scala:155)
        at dotty.tools.backend.jvm.CodeGen.genClassDef$1(CodeGen.scala:63)
        at dotty.tools.backend.jvm.CodeGen.genClassDefs$1(CodeGen.scala:118)
        - locked <0x0000000608f67650> (a java.lang.Object)
        at dotty.tools.backend.jvm.CodeGen.genClassDefs$1$$anonfun$1(CodeGen.scala:116)
        at dotty.tools.backend.jvm.CodeGen$$Lambda$2699/0x00000008007827d8.applyVoid(Unknown Source)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.backend.jvm.CodeGen.genClassDefs$1(CodeGen.scala:116)
        at dotty.tools.backend.jvm.CodeGen.genUnit(CodeGen.scala:121)
        at dotty.tools.backend.jvm.GenBCode.run(GenBCode.scala:83)

Thread 2:

"dotc-genBCode-non-ast-1" #37 daemon prio=5 os_prio=31 cpu=43.99ms elapsed=1205.38s tid=0x000000013c3c2000 nid=0xad0b waiting for monitor entry  [0x00000001755f1000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at dotty.tools.backend.jvm.CoreBTypesFromSymbols.jliLambdaMetaFactoryAltMetafactoryHandle$lzyINIT1(CoreBTypes.scala:170)
        - waiting to lock <0x0000000608f67650> (a java.lang.Object)
        at dotty.tools.backend.jvm.CoreBTypesFromSymbols.jliLambdaMetaFactoryAltMetafactoryHandle(CoreBTypes.scala:170)
        at dotty.tools.backend.jvm.BackendUtils.collectSerializableLambdas$$anonfun$1(BackendUtils.scala:58)
        at dotty.tools.backend.jvm.BackendUtils$$Lambda$2821/0x00000008007c8970.applyVoid(Unknown Source)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.IterableOnceOps.foreach(IterableOnce.scala:576)
        at scala.collection.IterableOnceOps.foreach$(IterableOnce.scala:574)
        at scala.collection.AbstractIterable.foreach(Iterable.scala:933)
        at dotty.tools.backend.jvm.BackendUtils.collectSerializableLambdas(BackendUtils.scala:68)
        at dotty.tools.backend.jvm.PostProcessor.setSerializableLambdas(PostProcessor.scala:88)
        at dotty.tools.backend.jvm.PostProcessor.sendToDisk(PostProcessor.scala:35)
        at dotty.tools.backend.jvm.GeneratedClassHandler$WritingClassHandler.postProcessUnit$$anonfun$1$$anonfun$1$$anonfun$1(GeneratedClassHandler.scala:95)
        at dotty.tools.backend.jvm.GeneratedClassHandler$WritingClassHandler$$Lambda$2820/0x00000008007c5710.applyVoid(Unknown Source)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.backend.jvm.GeneratedClassHandler$WritingClassHandler.postProcessUnit$$anonfun$1$$anonfun$1(GeneratedClassHandler.scala:95)
        at dotty.tools.backend.jvm.GeneratedClassHandler$WritingClassHandler.postProcessUnit$$anonfun$1$$anonfun$adapted$1(GeneratedClassHandler.scala:97)
        at dotty.tools.backend.jvm.GeneratedClassHandler$WritingClassHandler$$Lambda$2819/0x00000008007c5228.apply(Unknown Source)
        at dotty.tools.backend.jvm.PostProcessorFrontendAccess$Impl.withThreadLocalReporter(PostProcessorFrontendAccess.scala:116)
        at dotty.tools.backend.jvm.GeneratedClassHandler$WritingClassHandler.postProcessUnit$$anonfun$1(GeneratedClassHandler.scala:97)
        at dotty.tools.backend.jvm.GeneratedClassHandler$WritingClassHandler.postProcessUnit$$anonfun$adapted$1(GeneratedClassHandler.scala:97)
        at dotty.tools.backend.jvm.GeneratedClassHandler$WritingClassHandler$$Lambda$2817/0x00000008007c3cb0.apply(Unknown Source)

Output

Expectation
@WojciechMazur WojciechMazur self-assigned this Dec 18, 2023
This was referenced Dec 19, 2023
Closed
Merged
WojciechMazur added a commit that referenced this issue Dec 20, 2023
@WojciechMazur
Fix deadlock in initialization of CoreBTypes using Lazy container (#1…
33bdaac 
…9298)

Replaces #19297 and fixes #19293 

The deadlocks are now fixed by introduction of
`PostProcessorFrontendAccess.Lazy[T]` container for which initialization
is synchronized with the frontend Context, while providing a thread-safe
access lacking in original solution.

It now also audits where the unrestricted access to context was used and
replaces these usages with safer access.
Reverts #19292
odersky pushed a commit to dotty-staging/dotty that referenced this issue Jan 6, 2024
@WojciechMazur @odersky
Fix deadlock in initialization of CoreBTypes using Lazy container (sc…
57f2694 
…ala#19298)

Replaces scala#19297 and fixes scala#19293 

The deadlocks are now fixed by introduction of
`PostProcessorFrontendAccess.Lazy[T]` container for which initialization
is synchronized with the frontend Context, while providing a thread-safe
access lacking in original solution.

It now also audits where the unrestricted access to context was used and
replaces these usages with safer access.
Reverts scala#19292
WojciechMazur added a commit that referenced this issue Jul 10, 2024
@WojciechMazur
Fix deadlock in initialization of CoreBTypes using Lazy container (#1…
ea71c64 
…9298)

Replaces #19297 and fixes #19293 

The deadlocks are now fixed by introduction of
`PostProcessorFrontendAccess.Lazy[T]` container for which initialization
is synchronized with the frontend Context, while providing a thread-safe
access lacking in original solution.

It now also audits where the unrestricted access to context was used and
replaces these usages with safer access.
Reverts #19292
[Cherry-picked 33bdaac][modified]
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