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[browser][coreCLR] event pipe and browser profiler - #126324
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Pull request overview
Enables EventPipe/diagnostic-server plumbing for CoreCLR in browser by turning on FEATURE_PERFTRACING while keeping FEATURE_EVENT_TRACE disabled, and adds the browser-side scheduling + WebSocket/JS transport needed to drive the diagnostic server loop.
Changes:
- Enable
FEATURE_PERFTRACINGfor browser CoreCLR and gate ETW/EventTrace-specific code behindFEATURE_EVENT_TRACE(including EventPipe codegen changes). - Add browser-native diagnostic server job queue + scheduler callback wiring (
SystemJS_*DiagnosticServer*). - Add JS diagnostics client/transport (WebSocket + in-browser “js://” scenarios) and expose
ds_rt_websocket_*+dotnetApi.collect*helpers.
Reviewed changes
Copilot reviewed 42 out of 43 changed files in this pull request and generated 14 comments.
Show a summary per file
| File | Description |
|---|---|
| src/native/libs/System.Native.Browser/utils/scheduling.ts | Runs the diagnostic server callback alongside other background callbacks; abort clears pending diagnostic server timer id. |
| src/native/libs/System.Native.Browser/native/scheduling.ts | Adds SystemJS_ScheduleDiagnosticServer scheduling hook using safeSetTimeout. |
| src/native/libs/System.Native.Browser/native/index.ts | Exposes diagnostic server scheduler + callback through the native exports table; exports ds websocket shims. |
| src/native/libs/System.Native.Browser/native/diagnostics.ts | Adds native-side re-exports for ds_rt_websocket_* via diagnostics cross-module exports. |
| src/native/libs/System.Native.Browser/diagnostics/types.ts | Introduces diagnostics protocol/session/provider types and enums used by the JS diagnostics client. |
| src/native/libs/System.Native.Browser/diagnostics/index.ts | Wires diagnostics exports table and installs JS diagnostics client + dotnetApi helpers. |
| src/native/libs/System.Native.Browser/diagnostics/dotnet-gcdump.ts | Adds JS helper to collect gcdump trace via diagnostic server protocol. |
| src/native/libs/System.Native.Browser/diagnostics/dotnet-cpu-profiler.ts | Adds JS helper to collect CPU samples via diagnostic server protocol. |
| src/native/libs/System.Native.Browser/diagnostics/dotnet-counters.ts | Adds JS helper to collect metrics via diagnostic server protocol. |
| src/native/libs/System.Native.Browser/diagnostics/diagnostics.ts | Implements browser-side ds_rt_websocket_* transport and DS router reconnection support. |
| src/native/libs/System.Native.Browser/diagnostics/diagnostics-ws.ts | Implements WebSocket-based diagnostic connection wrapper. |
| src/native/libs/System.Native.Browser/diagnostics/diagnostics-js.ts | Implements in-browser “JS diagnostic client” session handling and scenario-based commands. |
| src/native/libs/System.Native.Browser/diagnostics/common.ts | Shared base queue/recv logic and trace download helper. |
| src/native/libs/System.Native.Browser/diagnostics/client-commands.ts | Implements serialization for diagnostic IPC commands (advertise, EventPipe commands, etc.). |
| src/native/libs/System.Native.Browser/ds.h | Adds placeholder header for diagnostic server C support. |
| src/native/libs/System.Native.Browser/ds.c | Adds native diagnostic server job queue + callback executor for browser builds. |
| src/native/libs/System.Native.Browser/CMakeLists.txt | Links ds.c into System.Native.Browser-Static. |
| src/native/libs/Common/JavaScript/types/public-api.ts | Updates diagnostics public types (providerName). |
| src/native/libs/Common/JavaScript/types/exchange.ts | Extends exchange tables/types for new native browser + diagnostics exports. |
| src/native/libs/Common/JavaScript/types/ems-ambient.ts | Adds ambient symbol + timer id tracking for diagnostic server callback scheduling. |
| src/native/libs/Common/JavaScript/loader/dotnet.d.ts | Updates generated public type surface (providerName). |
| src/native/libs/Common/JavaScript/cross-module/index.ts | Updates cross-module table mapping for new native browser + diagnostics exports. |
| src/native/eventpipe/ds-ipc-pal-websocket.h | Adds C linkage guards for websocket PAL APIs. |
| src/mono/mono/utils/mono-threads.h | Renames/aligns DS job queue API name to SystemJS_DiagnosticServerQueueJob. |
| src/mono/mono/utils/mono-threads-wasm.h | Renames DS exec callback export to SystemJS_ExecuteDiagnosticServerCallback. |
| src/mono/mono/utils/mono-threads-wasm.c | Renames DS queue/exec functions for browser single-threaded mode. |
| src/mono/mono/mini/mini-wasm.c | Updates exported symbol name for DS exec callback. |
| src/mono/mono/eventpipe/ep-rt-mono.h | Updates DS job rescheduling callsite to new queue function name. |
| src/mono/browser/runtime/types/internal.ts | Updates runtime helper name for DS exec callback. |
| src/mono/browser/runtime/exports.ts | Exposes renamed DS exec callback in runtime exports. |
| src/mono/browser/runtime/diagnostics/common.ts | Calls renamed DS exec callback from mono browser diagnostics event loop. |
| src/mono/browser/runtime/cwraps.ts | Updates cwrap signature to match renamed DS exec callback export. |
| src/coreclr/vm/qcallentrypoints.cpp | Gates NativeRuntimeEventSource QCalls behind FEATURE_EVENT_TRACE while keeping EventPipe QCalls under FEATURE_PERFTRACING. |
| src/coreclr/vm/nativeeventsource.cpp | Adds non-ETW stubs when FEATURE_PERFTRACING is enabled but FEATURE_EVENT_TRACE is disabled. |
| src/coreclr/vm/gcenv.ee.cpp | Wraps ETW-only GC analysis events with FEATURE_EVENT_TRACE guards. |
| src/coreclr/vm/eventing/eventpipe/ep-rt-coreclr.h | Adds browser single-threaded job queue integration via SystemJS_DiagnosticServerQueueJob; gates ETW-only provider init behind FEATURE_EVENT_TRACE. |
| src/coreclr/vm/eventing/eventpipe/CMakeLists.txt | Adds --noetwcallbacks option for EventPipe codegen when FEATURE_EVENT_TRACE is off. |
| src/coreclr/vm/eventing/CMakeLists.txt | Makes dependency on eventprovider conditional. |
| src/coreclr/scripts/genEventPipe.py | Adds --noetwcallbacks support to omit ETW callback wiring in generated provider code. |
| src/coreclr/nativeaot/Runtime/disabledruntimeeventinternal.cpp | Fixes a typo in a comment. |
| src/coreclr/clrfeatures.cmake | Enables FEATURE_PERFTRACING for browser targets; adjusts feature enablement logic. |
| src/coreclr/clrdefinitions.cmake | Ensures FEATURE_PERFTRACING defines and avoids creating dummy targets when perftracing is enabled. |
| src/coreclr/clr.featuredefines.props | Enables perf tracing for browser build configuration. |
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Summary
This change builds on top of EventPipe-for-CoreCLR (#128745) and adds two WASM profiling experiences for the CoreCLR interpreter on single-threaded browser/WASI builds:
.nettraceCPU samples consumable bydotnet-trace/ the JScollectCpuSamplesAPI.performance.measure()calls so managed method execution shows up as a nested flame chart in the browser Performance tab.Both are opt-in via the
DOTNET_WasmPerformanceInstrumentationMethodSet filter and are wired up through the existingWasmPerformanceInstrumentationMSBuild property (CoreCLR-compatible syntax).Motivation
On the multi-threaded runtime the EventPipe sample profiler runs on a dedicated thread that suspends the target. On single-threaded WASM there is no such thread, so the previous
ep_rt_sample_profiler_*hooks were no-ops and CPU sampling was unavailable for CoreCLR. This adds a cooperative sampling mechanism driven by the interpreter, matching the capability Mono already provides on the browser.How it works
New interpreter opcodes
Three opcodes are added in intops.def:
INTOP_PROF_SAMPLEPOINT— emitted at method entry and at backward branches (loop back-edges, alongside the existingINTOP_SAFEPOINT). Drives the EventPipe sampling profiler.INTOP_PROF_ENTER/INTOP_PROF_LEAVE— emitted at method entry/return (and tail-call / exception unwind paths). Drive the browser DevTools profiler.The interpreter compiler only emits these when the method matches the
WasmPerformanceInstrumentationMethodSet filter, and only onPERFTRACING_DISABLE_THREADS(single-threaded) builds.INTOP_PROF_ENTER/INTOP_PROF_LEAVEare additionally gated onTARGET_BROWSER.EventPipe CPU sampling (single-threaded)
ep-rt-coreclr-wasm-sampling.cpp implements the
ep_rt_coreclr_sample_profiler_*callbacks (now wired from ep-rt-coreclr.h instead of being no-ops).SamplingProfiler_OnSamplepoint()is invoked from the interpreter at samplepoints and:ep-rt-mono-runtime-provider.c).On multi-threaded builds the callbacks remain no-ops (the threaded profiler is used).
Browser DevTools profiler
browserprofiler.cpp maintains a shadow stack of method enter/leave timings and calls
ds_rt_browser_performance_measure()(→performance.measure()) so methods appear as nested entries in the browser Performance/flame chart. Recording is rate-limited with an adaptive skip counter; the shadow stack always tracks enter/leave for correctness, and a parent frame is marked for recording when a child is recorded so the chart nests properly. Leave only pops when the top frame matches, guarding against mismatched enter/leave for filtered-out methods.Configuration / MSBuild
RELEASE_CONFIG_METHODSET(WasmPerformanceInstrumentation)in interpconfigvalues.h.jitStartupenables the profilers when the filter is non-empty, before any managed code is compiled.WasmPerformanceInstrumentationproperty (e.g.all,interval=0) into CoreCLR env vars (DOTNET_WasmPerformanceInstrumentation, sampling-rate var), withallmapped to the MethodSet wildcard*. Native build is forced on when the property is set.Tests
Wasm.Build.Tests.Blazor.EventPipeDiagnosticsTestsis added to BuildWasmAppsJobsListCoreCLR.txt so it runs for CoreCLR.monocategory so it runs on CoreCLR; split the AOT (Mono-only) case into its ownnative-mono[Fact]while the Debug/Release non-AOT cases run for both runtimes.collectCpuSamples/collectGcDump/collectMetricsfrom the DevTools console.