fix(java): prevent ClassPrepareEvent from resuming stopped threads#27
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debugmcpdev merged 2 commits intodebugmcp:mainfrom Mar 28, 2026
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… event loop When an EventSet contains both a stopping event (breakpoint, step, exception) and a ClassPrepareEvent, the ClassPrepareEvent's `resume = true` overwrites the stopping event's `resume = false`. This causes the thread to be resumed before evaluate_expression can access it, resulting in "Thread has been resumed" errors. Track whether a stopping event was seen in the current EventSet and only allow ClassPrepareEvent to set resume=true if no stopping event occurred. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
…ondition Adds a test that verifies evaluate_expression works when a BreakpointEvent with suspendPolicy="thread" fires while a ClassPrepareRequest is active for a not-yet-loaded class. Before the fix, the ClassPrepareEvent could override the breakpoint's resume=false flag, causing "Thread has been resumed" errors. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Thanks for this fix, @Finomosec! The root cause analysis was spot-on, and the Merged as-is — nice work. |
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Summary
ClassPrepareEventin the sameEventSetas aBreakpointEventwould overrideresume = falsewithresume = true, incorrectly resuming the stopped thread"Thread has been resumed"errors when callingevaluate_expressionafter a breakpoint hit, especially withsuspendPolicy="thread"stoppedflag that prevents non-stopping events (ClassPrepare) from overriding the suspension decision of stopping events (Breakpoint, Step, Exception)Root Cause
In
JdiDapServer.java's event loop, events in anEventSetare processed sequentially. ABreakpointEventsetsresume = false, but a subsequentClassPrepareEventin the same set overwrites it withresume = true. TheeventSet.resume()at the end then resumes the thread before any evaluation can occur.Test plan
mcp-server-smoke-java-event-race.test.ts) that:suspendPolicy="thread"in main classClassPrepareRequest)evaluate_expressionsucceeds at the breakpoint (would fail before fix)suspendPolicy="thread", verify evaluation works🤖 Generated with Claude Code