When Should You Use GC.Collect() in .NET?

When to use GC.Collect() in .NET?

It is generally recommended to avoid calling GC.Collect() directly in your code, but there are certain exceptions. Understanding these exceptions can help optimize performance in specific scenarios.

GC.Collect() Acceptable usage scenarios:

• Hibernating Services: If a service intermittently wakes up to perform tasks and then goes into a long sleep state, it may be beneficial to start a garbage collection. This prevents inactive processes from retaining unnecessary memory.
• Resource cleanup after closing large forms: When closing large forms, many UI controls will become recyclable garbage. Forcing immediate garbage collection will allow the .NET Framework to recycle these objects, preventing users from noticing noticeable performance pauses.

Additional notes for .NET 4.5 and above:

In .NET 4.5 and above, additional scenarios occur:

• GCLatencyMode.LowLatency and GCLatencyMode.SustainedLowLatency: It is recommended to use GC.Collect(2, GCCollectionMode.Forced) to force a full garbage collection when entering or exiting these modes.
• GC.TryStartNoGCRegion: Using this method may result in a completely blocking garbage collection to free memory. To ensure stability, consider performing a full garbage collection before and after.

Reference and further reading:

• Writing High-Performance .NET Code, 2nd Edition, 2018 Author: Microsoft Engineer Ben Watson.
• MSDN: System.Runtime.GCLatencyMode
• MSDN: GC.TryStartNoGCRegion method

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