From e99af794a9d9e567ac50011cc45e2ddb6b0f3d52 Mon Sep 17 00:00:00 2001 From: Mitchell Hwang Date: Thu, 2 Jul 2026 17:58:12 -0400 Subject: [PATCH 1/3] Document EventPipe buffering mode and Event ID filter client APIs Add Microsoft.Diagnostics.NETCore.Client reference for EventPipeBufferingMode, EventPipeProviderEventFilter, the new EventPipeSessionConfiguration and EventPipeProvider overloads and properties, and the UnknownCommandException and InvalidCommandArgumentException types. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> --- .../microsoft-diagnostics-netcore-client.md | 118 +++++++++++++++++- 1 file changed, 116 insertions(+), 2 deletions(-) diff --git a/docs/core/diagnostics/microsoft-diagnostics-netcore-client.md b/docs/core/diagnostics/microsoft-diagnostics-netcore-client.md index 01c03a8f71f60..646bca851dace 100644 --- a/docs/core/diagnostics/microsoft-diagnostics-netcore-client.md +++ b/docs/core/diagnostics/microsoft-diagnostics-netcore-client.md @@ -1,10 +1,11 @@ --- title: Microsoft.Diagnostics.NETCore.Client API description: In this article, you'll learn about the Microsoft.Diagnostics.NETCore.Client APIs. -ms.date: 12/08/2025 +ms.date: 07/02/2026 author: tommcdon ms.author: tommcdon ms.topic: reference +ai-usage: ai-assisted --- # Microsoft.Diagnostics.NETCore.Client API @@ -343,6 +344,13 @@ public sealed class EventPipeSessionConfiguration long rundownKeyword, bool requestStackwalk = true); + public EventPipeSessionConfiguration( + IEnumerable providers, + int circularBufferSizeMB, + long rundownKeyword, + bool requestStackwalk, + EventPipeBufferingMode bufferingMode); + public bool RequestRundown { get; } public int CircularBufferSizeInMB { get; } @@ -351,6 +359,8 @@ public sealed class EventPipeSessionConfiguration public long RundownKeyword { get; } + public EventPipeBufferingMode BufferingMode { get; } + public IReadOnlyCollection Providers { get; } } ``` @@ -362,6 +372,9 @@ Represents the configuration for an `EventPipeSession`. * `requestRundown` : If `true`, request rundown events from the runtime. * `requestStackwalk` : If `true`, record a stack trace for every emitted event. * `rundownKeyword` : The keyword mask used for rundown events. +* `bufferingMode` : The [`EventPipeBufferingMode`](#eventpipebufferingmode-enum) for the session. Use `Block` to request non-lossy collection. Passing `Block` requires a .NET 11+ target runtime; on an older runtime, `StartEventPipeSession` throws [`UnknownCommandException`](#unknowncommandexception). + +The `BufferingMode` property returns the buffering mode for the session. The default value, `Drop`, keeps the runtime's lossy circular buffer. ## EventPipeProvider class @@ -374,6 +387,13 @@ public class EventPipeProvider long keywords = 0, IDictionary arguments = null) + public EventPipeProvider( + string name, + EventLevel eventLevel, + long keywords, + IDictionary arguments, + EventPipeProviderEventFilter eventFilter) + public string Name { get; } public EventLevel EventLevel { get; } @@ -382,6 +402,8 @@ public class EventPipeProvider public IDictionary Arguments { get; } + public EventPipeProviderEventFilter EventFilter { get; } + public override string ToString(); public override bool Equals(object obj); @@ -402,9 +424,16 @@ public EventPipeProvider( EventLevel eventLevel, long keywords = 0, IDictionary arguments = null) + +public EventPipeProvider( + string name, + EventLevel eventLevel, + long keywords, + IDictionary arguments, + EventPipeProviderEventFilter eventFilter) ``` -Creates a new instance of `EventPipeProvider` with the given provider name, , keywords, and arguments. +Creates a new instance of `EventPipeProvider` with the given provider name, , keywords, and arguments. The second overload also takes an [`EventPipeProviderEventFilter`](#eventpipeprovidereventfilter-class) that filters which Event IDs the runtime enables for the provider. When you set an event filter, the session requires a .NET 10+ target runtime. ### Name property @@ -438,10 +467,64 @@ public IDictionary Arguments { get; } Gets an `IDictionary` of key-value pair strings representing optional arguments to be passed to `EventSource` representing the given `EventPipeProvider`. +### EventFilter property + +```csharp +public EventPipeProviderEventFilter EventFilter { get; } +``` + +Gets the optional [`EventPipeProviderEventFilter`](#eventpipeprovidereventfilter-class) that the runtime applies to this provider's Event IDs after the keyword and level filter. When the value is `null`, the runtime enables every Event ID that the keyword and level filter allows. + ### Remarks This class is immutable, because EventPipe does not allow a provider's configuration to be modified during an EventPipe session as of .NET Core 3.1. +## EventPipeProviderEventFilter class + +```csharp +public sealed class EventPipeProviderEventFilter +{ + public EventPipeProviderEventFilter( + bool enable, + IReadOnlyList eventIds); + + public bool Enable { get; } + + public IReadOnlyList EventIds { get; } +} +``` + +Represents an optional per-provider filter on Event IDs. The runtime applies the filter after the keyword and level filter of the associated [`EventPipeProvider`](#eventpipeprovider-class). Event filters require a .NET 10+ target runtime. + +### Constructor + +```csharp +public EventPipeProviderEventFilter( + bool enable, + IReadOnlyList eventIds); +``` + +Creates a new instance of `EventPipeProviderEventFilter`. + +* `enable` : If `true`, `eventIds` is an allow-list and the runtime enables only those Event IDs. If `false`, `eventIds` is a deny-list and the runtime enables every Event ID except those listed. An empty deny-list therefore enables all events. +* `eventIds` : The Event IDs to enable or disable, as determined by `enable`. + +### Enable property + +```csharp +public bool Enable { get; } +``` + +Gets a value that indicates whether [`EventIds`](#eventids-property) is an allow-list (`true`) or a deny-list (`false`). + +### EventIds property + +```csharp +public IReadOnlyList EventIds { get; } +``` + +Gets the list of Event IDs that the filter enables or disables. + ## EventPipeSession class ```csharp @@ -576,6 +659,21 @@ Represents the type of perf map behavior that can be enabled. * `JitDump` : Enable JIT dump perf map output. * `PerfMap` : Enable traditional perf map output. +## EventPipeBufferingMode enum + +```csharp +public enum EventPipeBufferingMode +{ + Drop = 0, + Block = 1 +} +``` + +Controls how the runtime's per-session event buffer behaves when it fills faster than the session drains it. + +* `Drop` : The runtime default. The session uses a circular buffer that drops events when it overflows, so collection is lossy. +* `Block` : Non-lossy collection. The runtime blocks event producers until the reader frees buffer capacity instead of dropping events. Use it for collections that must be complete, such as a heap snapshot on a large heap. `Block` requires a .NET 11+ target runtime; on an older runtime, starting the session throws [`UnknownCommandException`](#unknowncommandexception). + ## Exceptions Exceptions that are thrown from the library are of type `DiagnosticsClientException` or a derived type. @@ -592,6 +690,22 @@ public class UnsupportedCommandException : DiagnosticsClientException This may be thrown when the command is not supported by either the library or the target process's runtime. +### UnknownCommandException + +```csharp +public class UnknownCommandException : UnsupportedCommandException +``` + +This is thrown when the target runtime doesn't recognize the requested command, typically because the runtime is too old to support it. For example, `StartEventPipeSession` throws it when you request [`EventPipeBufferingMode.Block`](#eventpipebufferingmode-enum) on a runtime older than .NET 11. Because it derives from `UnsupportedCommandException`, an existing `catch (UnsupportedCommandException)` still catches it. + +### InvalidCommandArgumentException + +```csharp +public class InvalidCommandArgumentException : UnsupportedCommandException +``` + +This is thrown when the target runtime recognizes the command but rejects its payload argument. + ### UnsupportedProtocolException ```csharp From 32ff3aaa4fceb7f7262db4566f87717d681b8e4c Mon Sep 17 00:00:00 2001 From: Mitchell Hwang Date: Thu, 2 Jul 2026 17:58:12 -0400 Subject: [PATCH 2/3] Document --buffering-mode for dotnet-gcdump and dotnet-trace dotnet-gcdump collect/report default to non-lossy (Block) with automatic fallback on older runtimes; dotnet-trace collect adds an opt-in --buffering-mode (default Drop). Block requires a .NET 11+ target runtime. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> --- docs/core/diagnostics/dotnet-gcdump.md | 26 ++++++++++++++++++++++---- docs/core/diagnostics/dotnet-trace.md | 11 ++++++++++- 2 files changed, 32 insertions(+), 5 deletions(-) diff --git a/docs/core/diagnostics/dotnet-gcdump.md b/docs/core/diagnostics/dotnet-gcdump.md index 1cdf928238476..a3a7b176f9abe 100644 --- a/docs/core/diagnostics/dotnet-gcdump.md +++ b/docs/core/diagnostics/dotnet-gcdump.md @@ -1,8 +1,9 @@ --- title: dotnet-gcdump diagnostic tool - .NET CLI description: Learn how to install and use dotnet-gcdump CLI tool to collect GC (Garbage Collector) dumps of live .NET processes using the .NET EventPipe. -ms.date: 06/03/2025 +ms.date: 07/02/2026 ms.topic: reference +ai-usage: ai-assisted --- # Heap analysis tool (dotnet-gcdump) @@ -46,6 +47,9 @@ The `dotnet-gcdump` global tool collects GC (Garbage Collector) dumps of live .N - Analyzing roots of objects (answering questions like, "what still has a reference to this type?"). - Collecting general statistics about the counts of objects on the heap. +> [!NOTE] +> `dotnet-gcdump collect` and `report` default to non-lossy (`Block`) buffering, which produces complete dumps on large heaps. `Block` requires a .NET 11+ target runtime; on older runtimes the tool automatically falls back to the lossy buffer. + ### View the GC dump captured from dotnet-gcdump On Windows, `.gcdump` files can be viewed in [PerfView](https://github.com/microsoft/perfview) for analysis or in Visual Studio. Currently, there is no way of opening a `.gcdump` on non-Windows platforms. @@ -80,7 +84,7 @@ Collects a GC dump from a currently running process. ### Synopsis ```console -dotnet-gcdump collect [-h|--help] [-p|--process-id ] [-o|--output ] [-v|--verbose] [-t|--timeout ] [-n|--name ] [--dsrouter ] +dotnet-gcdump collect [-h|--help] [-p|--process-id ] [-o|--output ] [-v|--verbose] [-t|--timeout ] [-n|--name ] [--dsrouter ] [--buffering-mode ] ``` ### Options @@ -131,6 +135,13 @@ dotnet-gcdump collect [-h|--help] [-p|--process-id ] [-o|--output `** + + Sets how the runtime buffers events while the GC dump is collected. Accepts `0`/`Drop` or `1`/`Block` (case-insensitive), and defaults to `Block`. + + - `0` / `Drop`: the lossy circular buffer. Events are dropped when the buffer overflows. + - `1` / `Block` (default): non-lossy collection. The runtime blocks event producers until the buffer drains instead of overwriting events when the buffer fills, which produces a complete GC dump on large heaps. `Block` requires a .NET 11+ target runtime and can make collection slower because the target application pauses more while the GC dump is collected. On older runtimes, the tool automatically falls back to `Drop` (lossy). + > [!NOTE] > To collect a GC dump using `dotnet-gcdump`, it needs to be run as the same user as the user running target process or as root. Otherwise, the tool will fail to establish a connection with the target process. @@ -198,7 +209,7 @@ Generate a report from a previously generated GC dump or from a running process, ### Synopsis ```console -dotnet-gcdump report [-h|--help] [-p|--process-id ] [-t|--report-type ] +dotnet-gcdump report [-h|--help] [-p|--process-id ] [-t|--report-type ] [--buffering-mode ] ``` ### Options @@ -215,6 +226,13 @@ dotnet-gcdump report [-h|--help] [-p|--process-id ] [-t|--report-type `** + + When you report from a running process with `--process-id`, sets how the runtime buffers events while the GC dump is collected. Accepts `0`/`Drop` or `1`/`Block` (case-insensitive), and defaults to `Block`. The option has no effect when you report from an existing `.gcdump` file. + + - `0` / `Drop`: the lossy circular buffer. Events are dropped when the buffer overflows. + - `1` / `Block` (default): non-lossy collection. The runtime blocks event producers until the buffer drains instead of overwriting events when the buffer fills, which produces a complete report on large heaps. `Block` requires a .NET 11+ target runtime and can make collection slower because the target application pauses more while the GC dump is collected. On older runtimes, the tool automatically falls back to `Drop` (lossy). + ### Examples - Generate a heap statistics report from a previously created `.gcdump` file: @@ -253,7 +271,7 @@ dotnet-gcdump report [-h|--help] [-p|--process-id ] [-t|--report-type ] [--buffersize ] [--clreventlevel ] [--clrevents ] @@ -108,6 +110,13 @@ dotnet-trace collect ### Options +- **`--buffering-mode `** + + Sets how the runtime buffers events. Accepts `0`/`Drop` or `1`/`Block` (case-insensitive), and defaults to `Drop`. + + - `0` / `Drop` (default): the lossy circular buffer. Events are dropped when the buffer overflows. + - `1` / `Block`: non-lossy tracing. The runtime blocks the threads emitting events until the buffer drains instead of dropping events, which produces a complete trace. `Block` requires a .NET 11+ target runtime and can make the traced application slower because event-emitting threads pause while the buffer stays full. On older runtimes, starting the trace fails; retry with `Drop` (the default). + - **`--buffersize `** Sets the size of the in-memory buffer, in megabytes. Default 256 MB. From 9700933e35565d2f68f34ca969b7db18a57d32b1 Mon Sep 17 00:00:00 2001 From: Mitchell Hwang Date: Thu, 2 Jul 2026 17:58:12 -0400 Subject: [PATCH 3/3] Document non-lossy EventPipe buffering environment variables Add DOTNET_EventPipeBufferingMode and DOTNET_EventPipeOutputStreaming to the EventPipe environment-variable reference, and note the non-lossy opt-in on the circular-buffer guidance. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> --- docs/core/diagnostics/eventpipe.md | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/docs/core/diagnostics/eventpipe.md b/docs/core/diagnostics/eventpipe.md index 7e4b8ce8434c2..6683f21242369 100644 --- a/docs/core/diagnostics/eventpipe.md +++ b/docs/core/diagnostics/eventpipe.md @@ -1,8 +1,9 @@ --- title: EventPipe Overview description: Learn about EventPipe and how to use it for tracing your .NET applications to diagnose performance issues. -ms.date: 03/19/2026 +ms.date: 07/02/2026 ms.topic: overview +ai-usage: ai-assisted --- # EventPipe @@ -81,6 +82,12 @@ However, you can use the following environment variables to set up an EventPipe > [!NOTE] > If the target process writes events too frequently, it can overflow this buffer and some events might be dropped. If too many events are getting dropped, increase the buffer size to see if the number of dropped events reduces. If the number of dropped events does not decrease with a larger buffer size, it may be due to a slow reader preventing the target process' buffers from being flushed. + > + > As of .NET 11, a streaming session can opt into non-lossy buffering with `DOTNET_EventPipeBufferingMode=1` (or `--buffering-mode Block` in [dotnet-trace](./dotnet-trace.md)) to block the threads emitting events instead of dropping them. Non-lossy buffering trades application throughput for completeness. + +* `DOTNET_EventPipeBufferingMode`: Available in .NET 11 and later. Controls how the startup EventPipe session's buffer behaves when it fills faster than it's drained. Set it to `0` (default) for the lossy circular buffer that drops events on overflow, or `1` for non-lossy (Block) buffering, which pauses the threads that emit events until the buffer drains so that no events are dropped. Any other value falls back to `0`. This setting applies only to a streaming session (see `DOTNET_EventPipeOutputStreaming`); it's ignored for non-streaming file sessions. + +* `DOTNET_EventPipeOutputStreaming`: Set this to `1` to stream the startup EventPipe session's events continuously instead of buffering them and writing at process exit. A streaming session is required for `DOTNET_EventPipeBufferingMode=1` (non-lossy) to take effect. * `DOTNET_EventPipeProcNumbers`: Set this to `1` to enable capturing processor numbers in EventPipe event headers. The default value is `0`.