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Visual Studio Debugger and .NET Runtime: Parallel Stacks and Heap Snapshot Synchronization
Zo Vale
0 reputation · 21 Dec 2021, 15:37 UTC
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0 reputation · 21 Dec 2021, 15:37 UTC
When analyzing complex concurrency issues in .NET applications, developers often combine the Parallel Stacks window with Memory Profiling to correlate thread distribution with object retention. While the Parallel Stacks window provides a visual representation of call stacks across all threads, heap snapshots capture the state of managed memory at a specific point in time.
A challenge arises when attempting to synchronize these two diagnostic views during an active debugging session. Because heap snapshots can introduce significant performance overhead and pause the runtime, there is uncertainty regarding whether the thread states captured in the Parallel Stacks window remain perfectly aligned with the object references recorded in a snapshot taken milliseconds apart.
31775 reputation · 22 Dec 2021, 00:53 UTC
Yes – when you create a heap snapshot (dump) in Visual Studio, the Parallel Stacks window is populated from the thread list and stack frames contained in that dump, so the view reflects the exact state of the process at the instant the snapshot was taken.
visualstudioDebug → Save Dump As → Heap dump.Debug → Break All).Debug → Save Dump As…, select Heap dump, and save the .dmp file.Debug → Windows → Parallel Stacks.Threads window or SOS commands (!threads, !clrstack) in the Immediate Window.If symbols are not loaded, the Parallel Stacks window may show unresolved frames; in that case, reload symbols and repeat the snapshot.
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31,775 reputation · 22 Dec 2021, 03:07 UTC
The Parallel Stacks window shows a live enumeration of managed thread stacks. It refreshes every time you open the window or hit Refresh, and it is not tied to a particular heap snapshot. In contrast, a heap snapshot (taken via Diagnostic Tools → Memory Usage → Take Snapshot or Debug → Save Dump As → Heap dump) is a point‑in‑time capture that suspends the CLR for a brief GC pause. The two can only be guaranteed to match if you pause the process first, take a snapshot, and then view the Parallel Stacks from the same dump file (e.g., by opening the .dmp in VS). During an active debug session, the stack view and snapshot are independent and can drift by milliseconds or more.
So, to correlate them: