Draft: Add new loop detector by acturcu · Pull Request #921 · JetBrains/lincheck

acturcu · 2026-01-14T11:28:00Z

This PR contains the basic LoopDetector API. A small description:

For the moment, I've made the LoopDetector maintain a per thread state image with the next ideas:

Each thread has a queue of Methods Called
Each Method Called has an id, a depth and a stack of active loops
Each Active Loop has id, iteration count and whether they have been switched or are marked stuck. Counters for Switch and Stuck are individual.

For a thread when first entering a loop, we either create a dummy frame or use the one we are in and push a new ActiveLoop onto it. During the other iterations of the loop, the methodIds are verified to match, the counter is increased and the thresholds are verified. When finishing a loop it removes the ActiveLoop from the stack.

On method level, we verify the top method on the stack, and if it matches with the current methodId it means we encounter some recursion, so the depth counter is incremented. If the depth > threshold then for the time being we declare the loop as stuck and try to switch the thread. On method exit we either decrease the depth or we remove the method from the stack (depth is 0)

src/jvm/main/org/jetbrains/kotlinx/lincheck/strategy/managed/LoopDetector.kt

src/jvm/main/org/jetbrains/kotlinx/lincheck/strategy/managed/ManagedStrategy.kt

Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

…StartTracePoint is not added to the trace, but LoopEndTracePoint is, so the iterations are not grouped together

src/jvm/main/org/jetbrains/kotlinx/lincheck/trace/TraceNodes.kt

src/jvm/main/org/jetbrains/kotlinx/lincheck/trace/Utils.kt

src/jvm/main/org/jetbrains/kotlinx/lincheck/IdeaPlugin.kt

src/jvm/main/org/jetbrains/kotlinx/lincheck/trace/Utils.kt

eupp · 2026-02-01T14:40:13Z

src/jvm/main/org/jetbrains/kotlinx/lincheck/strategy/managed/ManagedStrategy.kt

+            methodName = "run",
+            methodType = Types.MethodType(Types.VOID_TYPE)
+        )
+        popMethodId(currentThreadId, methodId)


Let's instead add methods to loop detector:

fun beforeThreadRun(...) fun afterThreadRun(...)

src/jvm/main/org/jetbrains/kotlinx/lincheck/strategy/managed/ManagedStrategy.kt

…ror:` part

…agedStrategy.kt independent of the loop detection algorithm

@dmitrii-artuhov

* Fix a subtle bug involving checks for package names that were shadowed and re-located. The shadow jar plugin substitutes all string literals in the source code that contain names of relocated packages. So special care is required when performing checks against names of relocated packages. * Thanks to @dmitrii-artuhov for a clever hack on how to circumvent package shadowing in strings. Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

\

…tBrains#942) Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

…etBrains#946)

--------- Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

…ains#948) --------- Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com> Co-authored-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

--------- Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

Re-creation of two hash sets on each call can be accounted for generation 50% of memory allocations in reading trace.

…ail on exceptions (JetBrains#956)

…RecursiveSpinLockTwoStepRecursionEventsTest

…kip the loop detector

acturcu changed the title ~~Add new loop detector~~ Draft: Add new loop detector Jan 14, 2026

eupp requested changes Jan 18, 2026

View reviewed changes

acturcu closed this Jan 19, 2026

acturcu reopened this Jan 19, 2026

acturcu force-pushed the new-loop-detector branch from 89c7c33 to 686a7be Compare January 20, 2026 13:55

eupp and others added 16 commits January 29, 2026 13:23

remove old loop detector implementation

a44bfb1

Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

add a comment

1621de8

Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

Counter based loop detector

a3dcd65

add comment

3a5e42e

Add suggestions to LoopDetector.kt

376bd5f

Add suggestions in ManagedStrategy.kt

c1e4239

Add beginning of trace printer

7b37623

Commented out removed part of moveSpinCycleStartTracePoints()

8d2f2fc

Add initial try of spin cycle trace printing

a6277a9

Add independent method stack for the LoopDetector

570427a

Add methodId pop afterThreadException

bfaa4a8

Add cleanup for LoopDetector.kt

fd790f6

Replace threadDescriptor with threadId in LoopDetector.kt

0a11efd

Improve trace printing for loops

af61fb4

Fix for <iteration 1> appearing twice

447199e

fix missing ignored section at afterLoopExit

c41ab92

Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

acturcu force-pushed the new-loop-detector branch from 8c64d72 to c41ab92 Compare January 29, 2026 12:29

acturcu added 2 commits January 29, 2026 13:59

Fix indentation of loops in printed trace

aac85af

Add initial prettifying for loops. Known bug: for some tests the Loop…

76d8216

…StartTracePoint is not added to the trace, but LoopEndTracePoint is, so the iterations are not grouped together

eupp reviewed Feb 1, 2026

View reviewed changes

acturcu added 5 commits February 5, 2026 16:55

Fix iteration folding bug

1632b96

Add recursive calls folding

88196d8

Fix trace print for non-ranged iteration in `interleaving leads to er…

92160cb

…ror:` part

Merge IterationNode and IterationRangeNode together

e7212b4

Remove redundant convertOpenLoopsToSpinCycles() function

b0c4060

acturcu added 4 commits February 7, 2026 03:41

Remove comment & make RecursionNodes also unfold

5d3dc9b

Repair loop folding broken in previous commits

9b3d39a

Move functions from ManagedStrategy.kt to LoopDetector.kt to make Man…

f1ef538

…agedStrategy.kt independent of the loop detection algorithm

Improve loop folding to also fold structural similar traces

ac8af63

eupp mentioned this pull request Feb 10, 2026

Rebase new model checker #934

Draft

acturcu and others added 25 commits February 12, 2026 00:55

Add support for nested iteration folding

9beb7eb

Capture open telemetry trace ID (JetBrains#935)

5ce0d65

Add org.omg to instrumentation filters (JetBrains#939)

8b8979e

Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

fix CFG loop validation check (JetBrains#936)

7e1e03d

Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

Live debugger: safety checker for breakpoint conditions (JetBrains#925)

b2a52d5

\

Refactor TraceRecordingMode and related start/stop tracing APIs (Je…

ee82c30

…tBrains#942) Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

Make sure conditions do not contain loops (JetBrains#940)

5cab589

Fix stupid mistake which can lead to recursive tracing which fails. (J…

4700195

…etBrains#946)

Live debugger: collect trace points as flat list (JetBrains#943)

7ea426e

--------- Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

Prototype conditions for Live Debugger (JetBrains#945)

20e6f4d

Add JMX server shutdown hook (JetBrains#937)

9586468

Trace TCP streaming (JetBrains#941)

f40c58f

--------- Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

Add live debugger JMX controller API to add/remove breakpoints (JetBr…

5eea66b

…ains#948) --------- Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com> Co-authored-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

Capture Object fields and Array elements (JetBrains#947)

c1f62c9

quickfix for JetBrains#948

2b8a2f0

Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

Few minor logging infra improvements (JetBrains#949)

fd998f8

--------- Signed-off-by: Evgeniy Moiseenko <evg.moiseenko94@gmail.com>

Fix missing thread name after for TCP streaming (JetBrains#950)

a803ec3

Fix creation of tons of garbage. (JetBrains#951)

1a41d86

Re-creation of two hash sets on each call can be accounted for generation 50% of memory allocations in reading trace.

Disable bytecode caching in Live Debugger mode (JetBrains#952)

57cfc5b

Bump ASM version to 9.9.1 (JetBrains#954)

3e8734f

Avoid duplicate breakpoint hits (JetBrains#955)

9b9aee9

Surround condition calls with try-catch blocks, assuming conditions f…

fe41cf6

…ail on exceptions (JetBrains#956)

Update test files - not including ValidationFunctionLongLoopTest and …

29b1426

…RecursiveSpinLockTwoStepRecursionEventsTest

Add a check to verify if the execution is in Validation in order to s…

8b2965b

…kip the loop detector

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Draft: Add new loop detector #921

Draft: Add new loop detector #921
acturcu wants to merge 56 commits intoJetBrains:developfrom
acturcu:new-loop-detector

acturcu commented Jan 14, 2026

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eupp Feb 1, 2026

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acturcu commented Jan 14, 2026

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eupp Feb 1, 2026

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