How to investigate high memory usage of a custom Roslyn Analyzer in Rider

Question

How can I diagnose and resolve high memory usage caused by a Roslyn analyzer using JetBrains Rider or other tools?

Answer

If your Roslyn analyzer consumes a large amount of memory, you can use dotMemory to diagnose the issue. Below is a step-by-step guide to identify and resolve memory leaks effectively:

1. Launch dotMemory

   • You can either launch dotMemory standalone or use the dotMemory tool window integrated in Rider.

2. Start Profiling the Roslyn Process

   • Locate the JetBrains.Roslyn.Worker process in the list of running processes.

   • Start profiling the process by double-clicking it or using a context menu action.

     

3. Collect Memory Snapshots

   • While the process is running, periodically collect memory snapshots by selecting the Get Snapshot action. Gather snapshots specifically when you notice an increase in memory usage.

     

4. Analyze Snapshots

   • Select multiple snapshots for comparison using the Add to comparison checkbox.

   • Use the View memory allocations option to analyze changes in memory usage between snapshots.

     

5. Inspect Suspicious Memory Usage

   • Switch between the Types and Methods tabs to identify abnormal memory allocations.

   • For example, in a hypothetical case, you may find that Byte[] objects are continuously allocated in large chunks by a method like AnalyzeInvocation(SyntaxNodeAnalysisContext). This will be indicated in the Types and Methods tabs and confirmed by looking at the source code of relevant methods:

     

     

     private static void AnalyzeInvocation(SyntaxNodeAnalysisContext context)
     {
         ...
         byte[] chunk = new byte[OneHundredMB]; //allocated in a loop
     }
     

6. Compare Snapshots Further (Optional)

   • Refer to the Compare Snapshots to understand the trend of object allocations and deallocations over time.
   • You may also inspect individual snapshots for deeper analysis by selecting an object set and following the Analyze Object Set guidelines.