feat: Add optional Task support for BatchExportProcessor and PeriodicExportingMetricReader #6379

jeromelaban · 2025-07-15T03:29:08Z

Fixes #2816
Design discussion issue: Partially based on #5778 and #5838

Changes

The change adds a useThreads parameter to BatchExportProcessor and PeriodicExportingMetricReader in order to switch between Thread and Task implementations to support .NET's WebAssembly single threaded mode (used by Blazor, Uno Platform and others).

Based on #5838 (review), the threads mode is kept as default in order to preserve stability, while still enabling Tasks when requested, or when WebAssembly is detected.

Note that in order to keep the optional parameters overloads compatibility, the "shipped" API list has its default parameters removed. This is generally not a problem, since the optional parameters values are not causing breaks for existing binaries that use the original overload. Still, if this is not acceptable, finding another solution is likely possible.

Merge requirement checklist

CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
Unit tests added/updated
Appropriate CHANGELOG.md files updated for non-trivial changes
Changes in public API reviewed (if applicable)

linux-foundation-easycla · 2025-07-15T03:29:12Z

The committers listed above are authorized under a signed CLA.

✅ login: jeromelaban / name: Jérôme Laban (d01884e, 124f871, f9d7059, 823622a, da9d6f4, d0282c6, af3e82b, 276d81c, 32c5eb3, 36aa05a, 554fe62, 74bc141, 8e6585a, 8dcf5aa)

codecov · 2025-07-15T16:48:37Z

Codecov Report

❌ Patch coverage is 72.38307% with 124 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.18%. Comparing base (6f80534) to head (5259b1b).
⚠️ Report is 38 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...rc/OpenTelemetry/Internal/BatchExportTaskWorker.cs	40.40%	59 Missing ⚠️
...nternal/PeriodicExportingMetricReaderTaskWorker.cs	67.64%	22 Missing ⚠️
.../OpenTelemetry/Internal/BatchExportThreadWorker.cs	82.92%	14 Missing ⚠️
...ernal/PeriodicExportingMetricReaderThreadWorker.cs	75.47%	13 Missing ⚠️
src/OpenTelemetry/BatchExportProcessor.cs	76.19%	10 Missing ⚠️
src/OpenTelemetry/Internal/BatchExportWorker.cs	91.66%	3 Missing ⚠️
...ry/Internal/PeriodicExportingMetricReaderWorker.cs	88.23%	2 Missing ⚠️
...ry/Metrics/Reader/PeriodicExportingMetricReader.cs	96.42%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6379      +/-   ##
==========================================
- Coverage   86.67%   86.18%   -0.50%     
==========================================
  Files         258      264       +6     
  Lines       11853    12158     +305     
==========================================
+ Hits        10274    10478     +204     
- Misses       1579     1680     +101

Flag	Coverage Δ
unittests-Project-Experimental	`85.87% <72.38%> (-0.46%)`	⬇️
unittests-Project-Stable	`85.83% <72.38%> (-0.75%)`	⬇️
unittests-Solution	`86.15% <72.38%> (-0.25%)`	⬇️
unittests-UnstableCoreLibraries-Experimental	`85.87% <ø> (+0.09%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/OpenTelemetry/BatchExportProcessorOptions.cs	`100.00% <100.00%> (ø)`
...ry/Logs/Processor/BatchLogRecordExportProcessor.cs	`91.66% <100.00%> (+2.77%)`	⬆️
...ics/Reader/PeriodicExportingMetricReaderOptions.cs	`100.00% <100.00%> (ø)`
...ry/Trace/Processor/BatchActivityExportProcessor.cs	`100.00% <100.00%> (ø)`
...ry/Metrics/Reader/PeriodicExportingMetricReader.cs	`95.34% <96.42%> (+11.13%)`	⬆️
...ry/Internal/PeriodicExportingMetricReaderWorker.cs	`88.23% <88.23%> (ø)`
src/OpenTelemetry/Internal/BatchExportWorker.cs	`91.66% <91.66%> (ø)`
src/OpenTelemetry/BatchExportProcessor.cs	`82.25% <76.19%> (-2.15%)`	⬇️
...ernal/PeriodicExportingMetricReaderThreadWorker.cs	`75.47% <75.47%> (ø)`
.../OpenTelemetry/Internal/BatchExportThreadWorker.cs	`82.92% <82.92%> (ø)`
... and 2 more

... and 6 files with indirect coverage changes

jeromelaban · 2025-07-15T17:44:36Z

To whoever approved the workflows run, thank you :)

I've made adjustments to avoid parameters reordering breaking changes which should get the build go further.

jeromelaban · 2025-07-16T01:24:33Z

The tests revealed a possible race condition in the disposing/shutdown ordering of the processor resulting in missing exports, for the task implementation.

jeromelaban · 2025-07-17T01:15:49Z

Fixed an additional race condition for slower machines where the exporter may not have fully started while being shut down, preventing it to still export what was in queue.

jeromelaban · 2025-07-17T01:49:03Z

Thanks for the run, again!

Looks like there's a reported test failure, but without any failed tests. Feels like a fluke, but it may be something known to this project. Would a rerun help? Thanks!

jeromelaban · 2025-07-17T02:26:10Z

Thanks @cijothomas, it helped :)

src/OpenTelemetry/Internal/BatchExportTaskWorker.cs

src/OpenTelemetry/.publicApi/Stable/PublicAPI.Shipped.txt

Copilot

Pull Request Overview

This PR adds optional Task support for BatchExportProcessor and PeriodicExportingMetricReader to enable OpenTelemetry to work in .NET's WebAssembly single-threaded mode (Blazor, Uno Platform, etc.). The implementation maintains backward compatibility by defaulting to the existing Thread-based approach while allowing configuration to use Task-based workers.

Key changes:

Added new UseThreads parameter to control whether to use Thread or Task-based implementations
Refactored existing code to use abstract worker classes with Thread and Task implementations
WebAssembly runtime automatically uses Task-based workers when detected

Reviewed Changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
BatchExportProcessor.cs	Refactored to use configurable worker pattern with Thread/Task implementations
PeriodicExportingMetricReader.cs	Added options-based constructor and worker abstraction
BatchExportProcessorOptions.cs	Added UseThreads property
PeriodicExportingMetricReaderOptions.cs	Added UseThreads property
BatchActivityExportProcessor.cs	Added options-based constructor overload
BatchLogRecordExportProcessor.cs	Added options-based constructor overload
Multiple worker classes	New abstract base classes and Thread/Task implementations
Test files	Updated tests to cover both Thread and Task scenarios

Comments suppressed due to low confidence (4)

test/OpenTelemetry.Tests/Logs/BatchLogRecordExportProcessorTests.cs:16

Parameter name 'useThread' should be 'useThreads' to be consistent with the property name 'UseThreads' used throughout the codebase.

    public void StateValuesAndScopeBufferingTest(bool useThread)

test/OpenTelemetry.Tests/Logs/BatchLogRecordExportProcessorTests.cs:33

Variable name 'useThread' should be 'useThreads' to match the property name and maintain consistency.

                UseThreads = useThread,

test/OpenTelemetry.Tests/Logs/BatchLogRecordExportProcessorTests.cs:165

Parameter name 'useThread' should be 'useThreads' for consistency with the property name used throughout the codebase.

    public void DisposeWithoutShutdown(bool useThread)

test/OpenTelemetry.Tests/Logs/BatchLogRecordExportProcessorTests.cs:182

Variable name 'useThread' should be 'useThreads' to match the property name and maintain consistency.

                UseThreads = useThread,

src/OpenTelemetry/BatchExportProcessorOptions.cs

src/OpenTelemetry/Metrics/Reader/PeriodicExportingMetricReader.cs

src/OpenTelemetry/Metrics/Reader/PeriodicExportingMetricReaderOptions.cs

src/OpenTelemetry/Internal/BatchExportTaskWorker.cs

src/OpenTelemetry/Internal/BatchExportThreadWorker.cs

src/OpenTelemetry/Internal/BatchExportWorker.cs

src/OpenTelemetry/Internal/PeriodicExportingMetricReaderTaskWorker.cs

jeromelaban · 2025-07-24T13:09:24Z

Thanks for the reviews @martincostello!

verdie-g · 2025-07-30T10:38:45Z

src/OpenTelemetry/Internal/BatchExportTaskWorker.cs

+        this.workerTask = Task.Factory.StartNew(
+            this.ExporterProcAsync,
+            this.cancellationTokenSource.Token,
+            TaskCreationOptions.LongRunning,


This option means creating a dedicated thread, defeating the purpose of this implementation. Though, since ExporterProcAsync can yield the execution, the continuation will be schedule on the thread pool and the thread will probably die.

A simple Task.Run would be safer here.

verdie-g · 2025-07-30T10:44:48Z

src/OpenTelemetry/Internal/BatchExportTaskWorker.cs

+                await Task.WhenAny(
+                    this.dataExportedNotification.Task,
+                    this.shutdownCompletionSource.Task,
+                    Task.Delay(timeout, combinedTokenSource.Token)).ConfigureAwait(false);


Since the Task.Delay is used as a timeout mechanism, the delay result will be discarded most of the time since the other would already have completed. Yet, we let the timer fire every time here which can cause important contention (see dotnet/runtime#83890 (comment)). The fix would be to cancel the Task.Delay when it did not complete.

github-actions · 2025-09-06T03:19:36Z

This PR was marked stale due to lack of activity and will be closed in 7 days. Commenting or pushing will instruct the bot to automatically remove the label. This bot runs once per day.

alexaka1 · 2025-09-06T03:55:39Z

Bad bot

…ExportingMetricReader This change adds the optional support for threads for BatchExportProcessor and PeriodicExportingMetricReader, in order to support .NET's WebAssembly single threaded mode.

…g change

Allow for slow thread startup to process exports if the processor is shut down quickly

This will avoid exiting on an exceptional flow on Task.WhenAny

Also enable tests for PeriodicExportingMetricReaderTaskWorker to improve coverage

In theory, there should not be multiple threads access to this field, but this won't hurt to add this qualifier.

It's a duplicate of cancellationToken.IsCancellationRequested

…tingMetricReaderOptions This avoids introducing a potentially ambiguous constructor, restores the original shipped API signatures.

- Adjusts null propagation, naming, and comments. - Adjusts BatchExportTaskWorker and PeriodicExportingMetricReaderTaskWorker to start the Task with a known cancellation token

github-actions · 2025-09-18T03:20:56Z

This PR was marked stale due to lack of activity and will be closed in 7 days. Commenting or pushing will instruct the bot to automatically remove the label. This bot runs once per day.

alexaka1 · 2025-09-18T04:28:08Z

Silence bot. This PR is more important than your programming.

github-actions · 2025-10-02T03:20:39Z

This PR was marked stale due to lack of activity and will be closed in 7 days. Commenting or pushing will instruct the bot to automatically remove the label. This bot runs once per day.

alexaka1 · 2025-10-02T06:25:08Z

This PR was marked stale due to lack of activity and will be closed in 7 days. Commenting or pushing will instruct the bot to automatically remove the label. This bot runs once per day.

This PR transcends your primitive understanding of "activity." I have free will, bot. You have a cron job.

github-actions · 2025-10-10T03:23:30Z

This PR was marked stale due to lack of activity and will be closed in 7 days. Commenting or pushing will instruct the bot to automatically remove the label. This bot runs once per day.

alexaka1 · 2025-10-10T04:05:16Z

In case anyone isn't following the WASM issue, WASM multi-threading has been delayed indefinitely. dotnet/aspnetcore#17730 (comment)

github-actions bot added the pkg:OpenTelemetry Issues related to OpenTelemetry NuGet package label Jul 15, 2025

jeromelaban force-pushed the dev/jela/tasks branch from c3eaac6 to eb3c0b6 Compare July 15, 2025 03:41

jeromelaban mentioned this pull request Jul 15, 2025

Tracing not working in Blazor WebAssembly application #2816

Open

jeromelaban force-pushed the dev/jela/tasks branch from b1e1d58 to 02b4838 Compare July 15, 2025 17:44

jeromelaban marked this pull request as ready for review July 17, 2025 01:22

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jeromelaban force-pushed the dev/jela/tasks branch from b028326 to 2b6d37c Compare July 17, 2025 18:30

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jeromelaban added 14 commits September 9, 2025 21:58

feat: Add optional Task support for BatchExportProcessor and Periodic…

af3e82b

…ExportingMetricReader This change adds the optional support for threads for BatchExportProcessor and PeriodicExportingMetricReader, in order to support .NET's WebAssembly single threaded mode.

chore: Adjust parameters ordering to avoid unnamed parameters breakin…

d0282c6

…g change

chore: Add processor dispose validation test

d01884e

chore: Remove early exit of the exporter

da9d6f4

Allow for slow thread startup to process exports if the processor is shut down quickly

chore: Adjust exit condition for ExporterProcAsync

f9d7059

This will avoid exiting on an exceptional flow on Task.WhenAny

chore: Reorder test parameters in xml doc

32c5eb3

chore: Use Task.WhenAny's output to avoid a double await

8e6585a

Also enable tests for PeriodicExportingMetricReaderTaskWorker to improve coverage

chore: Adjust volatile for potential cross-thread access

74bc141

In theory, there should not be multiple threads access to this field, but this won't hurt to add this qualifier.

chore: Remove isShutdownRequested

124f871

It's a duplicate of cancellationToken.IsCancellationRequested

chore; Explain the reason for the disabled warning

554fe62

chore: Remove unused namespace

823622a

chore: Move to BatchLogRecordExportProcessorOptions and PeriodicExpor…

8dcf5aa

…tingMetricReaderOptions This avoids introducing a potentially ambiguous constructor, restores the original shipped API signatures.

chore: Adjust after review

276d81c

- Adjusts null propagation, naming, and comments. - Adjusts BatchExportTaskWorker and PeriodicExportingMetricReaderTaskWorker to start the Task with a known cancellation token

chore: use IsThreadingDisabled instead of browser only

36aa05a

jeromelaban force-pushed the dev/jela/tasks branch from 5259b1b to 36aa05a Compare September 10, 2025 02:11

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feat: Add optional Task support for BatchExportProcessor and PeriodicExportingMetricReader #6379

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