Lease debugger sessions across commands

[max-charlamb]

Summary

• add a disposable debugger-session lease that keeps one pooled debugger host locked across multiple commands
• use the lease around the dbgout enable/use/disable sequence
• simplify dump-session slot ownership now that every dump debugger uses a bounded host pool
• keep in-process DbgEng dump capture concurrency separate from pooled dump analysis

Root cause

dbgout changes global state in the loaded SOS instance. Dump debugger hosts are pooled, but the existing slot lock covered each command independently. After one test enabled dbgout, another test could acquire the same physical debugger before the first test disabled it.

On .NET Framework dumps, clrstack -all -r can encounter native IPs that cannot be mapped back to managed source information. With dbgout unexpectedly enabled, those diagnostics were emitted into the command's tabular output while a row was being assembled. The test parser then interpreted the diagnostic text as part of the row and failed its register validation.

Fix

AcquireDebuggerSession now returns a disposable lease over the existing host-slot monitor. The SessionCommands_Execute test holds that lease from dbgout through the commands under test and the dbgout -off cleanup. Nested command acquisitions are reentrant on the same thread, so the same physical debugger remains exclusively owned until its global state is restored.

Testing

• built src/tests/SOS.Tests/SOS.Tests.csproj: zero warnings and errors
• ran HostSlotTests: 4 passed
• ran SessionCommands_Execute and ClrStack_Registers together for Framework/CDB dumps five times: 25 passed

CI failure

Addresses the Framework ClrStack_Registers failure in build 1598637.

[Copilot]

🔵 Needs a closer look

Add a cross-owner contention test proving a second session cannot acquire a slot before the outer lease is disposed.

Pull request overview

Adds disposable debugger-session leases to keep pooled dump hosts exclusive across multi-command sequences and isolate dbgout state.

Changes:

• Adds reentrant host-slot leases and bounded pooling.
• Protects the dbgout command sequence with a lease.
• Separates DbgEng capture serialization from dump-host pooling.

File summaries

File	Summary
src/tests/SOS.Tests/MiscCommandTests.cs	Holds a lease during dbgout operations.
src/tests/SOS.Tests/HostSlotTests.cs	Updates slot tests and adds lease coverage.
src/tests/SOS.TestHarness/Targets.cs	Simplifies pooled-host teardown.
src/tests/SOS.TestHarness/Target.cs	Adds the debugger-session lease API.
src/tests/SOS.TestHarness/HostSlot.cs	Implements pooled host ownership and leases.
src/tests/SOS.TestHarness/DumpSession.cs	Uses pooled slots for dump commands.
src/tests/SOS.TestHarness/DeadTarget.cs	Forwards lease acquisition to dump sessions.
src/tests/SOS.TestHarness/DbgEngCapturer.cs	Adds independent capture serialization.

Review details

Suppressed comments (1)

src/tests/SOS.Tests/HostSlotTests.cs:113

• This test only exercises reentrant acquisition by the same owner. It never tries to acquire the slot from a different owner while the outer lease is held, so it would still pass if the lease released the monitor between commands—the cross-session exclusivity that fixes the reported dbgout race is untested. Add a scheduler-safe contention assertion that a second owner cannot acquire until the outer lease is disposed.

        using (slot.Acquire(owner))
        {
            using (slot.Acquire(owner))
            {
                owner.Host.Sos("first");

• Files reviewed: 8/8 changed files
• Comments generated: 0
• Review effort level: Lite

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