Support hosted services in WebAssemblyHost #63814

Copilot · 2025-09-25T09:53:54Z

This PR adds support for hosted services (IHostedService) in WebAssemblyHost, enabling automatic startup and shutdown of background services in Blazor WebAssembly applications.

Description

Applications using WebAssemblyHost (e.g. Blazor WebAssembly clients) did not support hosted services out of the box. Services registered with AddHostedService were ignored when using WebAssemblyHostBuilder, unlike in applications built with WebApplicationBuilder or HostApplicationBuilder. This prevented libraries like OpenTelemetry from working properly in Blazor WebAssembly apps, as they rely on hosted services for initialization.

The implementation adds hosted service lifecycle management to WebAssemblyHost:

Service Discovery: Automatically discovers IHostedService implementations from the DI container
Startup Integration: Starts hosted services during RunAsyncCore() after component state restoration
Cleanup Integration: Stops hosted services during DisposeAsync() with proper error handling
HostedServiceExecutor: Encapsulates hosted service lifecycle logic in a dedicated executor class registered in DI, with integrated exception handling and logging using LoggerMessage source generator pattern
Clean Architecture: WebAssemblyHost simply resolves the executor from DI and calls it at the appropriate times, maintaining clean separation of concerns

Usage

Developers can now register hosted services in Blazor WebAssembly apps:

var builder = WebAssemblyHostBuilder.CreateDefault(args);

// Register hosted services - they'll start automatically
builder.Services.AddSingleton<IHostedService, MyBackgroundService>();

var host = builder.Build();
await host.RunAsync(); // Hosted services start here

Implementation Details

Added Microsoft.Extensions.Hosting.Abstractions reference to enable IHostedService support
Created HostedServiceExecutor class in the WebAssembly project to encapsulate hosted service lifecycle management
Registered HostedServiceExecutor as a singleton in DI in WebAssemblyHostBuilder.InitializeDefaultServices()
HostedServiceExecutor accepts ILogger<HostedServiceExecutor> and handles all exception aggregation and logging internally
Hosted services start after component state restoration (matching the timing suggested in the original issue)
Error handling ensures host disposal doesn't fail if hosted services throw exceptions during shutdown
Uses LoggerMessage source generator pattern for structured logging, following codebase conventions in WebAssemblyRenderer and WebAssemblyNavigationManager
WebAssemblyHost resolves the executor from DI and coordinates its invocation at the right times
Follows the same architectural pattern as the Hosting project for consistency across the codebase

Testing

Added comprehensive test coverage:

Service startup during host run
Service shutdown during host disposal
Error handling for faulty services
Integration with service registration patterns

All existing WebAssemblyHost functionality remains unchanged and all tests pass.

Original prompt

This section details on the original issue you should resolve

<issue_title>Support hosted services in WebAssemblyHost</issue_title>
<issue_description>### Is there an existing issue for this?

I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

Applications using WebAssemblyHost (e.g. Blazor WebAssembly clients) do not support hosted services out of the box. Services registered with AddHostedService are ignored when using WebAssemblyHostBuilder, unlike in applications built with WebApplicationBuilder or HostApplicationBuilder.

Describe the solution you'd like

WebAssemblyHost should support automatically running hosted services registered with AddHostedService.

Additional context

This feature request has already been rejected in #33537. However, we might want to reconsider the decision. For example, support for hosted services might be beneficial for Open Telemetry integration in Blazor Wasm apps.</issue_description>

<agent_instructions>Look at

aspnetcore/src/Hosting/Hosting/src/Internal/HostedServiceExecutor.cs

Line 10 in 063ba34

private readonly IEnumerable<IHostedService> _services;

and

aspnetcore/src/Hosting/Hosting/src/Internal/WebHost.cs

Line 30 in 063ba34

private HostedServiceExecutor? _hostedServiceExecutor;

We want WebAssemblyHost to start the services here https://github.com/dotnet/aspnetcore/blob/main/src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHost.cs#L139</agent_instructions>

Comments on the Issue (you are @copilot in this section)
@pavelsavara We should measure the size/perf impact of adding it by default for WASM

Fixes #63637

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Co-authored-by: javiercn <[email protected]>

Copilot

Pull request overview

This PR adds hosted service (IHostedService) lifecycle management to WebAssemblyHost, enabling Blazor WebAssembly applications to use background services automatically. This addresses the limitation where services registered with AddHostedService were previously ignored in WebAssembly applications, and was specifically requested to support libraries like OpenTelemetry that rely on hosted services.

Key changes:

Hosted services are automatically started during RunAsyncCore() after component state restoration
Hosted services are stopped during DisposeAsync() with error aggregation and logging
Added dependency on Microsoft.Extensions.Hosting.Abstractions to enable IHostedService support

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
`src/Components/WebAssembly/WebAssembly/src/Microsoft.AspNetCore.Components.WebAssembly.csproj`	Adds reference to `Microsoft.Extensions.Hosting.Abstractions` package
`src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHost.cs`	Implements hosted service lifecycle with start/stop methods and disposal integration
`src/Components/WebAssembly/WebAssembly/test/Microsoft.AspNetCore.Components.WebAssembly.Tests.csproj`	Adds reference to `Microsoft.Extensions.Hosting.Abstractions` for test project
`src/Components/WebAssembly/WebAssembly/test/Hosting/WebAssemblyHostTest.cs`	Adds comprehensive tests for hosted service startup, shutdown, and error handling scenarios

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Copilot · 2025-12-01T13:29:03Z

src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHost.cs

+                    var logger = Services.GetService<ILogger<WebAssemblyHost>>();
+                    logger?.LogError(ex, "An error occurred stopping hosted services during disposal.");


Consider using the LoggerMessage source generator pattern for structured logging. The codebase convention in WebAssemblyRenderer and WebAssemblyNavigationManager uses partial static Log classes with [LoggerMessage] attributes for better performance and consistency. Add a private static partial class Log with a LoggerMessage method for this error.

@copilot do this

Updated to use LoggerMessage source generator pattern with a private static partial Log class. Changes in commit d8752fb.

Copilot · 2025-12-01T13:29:03Z

src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHost.cs

+        }
+
+        // Throw an aggregate exception if there were any exceptions
+        if (exceptions is not null)


[nitpick] The condition check uses is not null which is correct according to nullable reference type conventions. However, the HostedServiceExecutor in src/Hosting/Hosting/src/Internal/HostedServiceExecutor.cs:43 uses != null for the same pattern. Consider using is not null consistently for better code alignment with C# null pattern matching practices, which this codebase already follows (see line 84, 105).

maraf

Looks good to me 👍

Co-authored-by: javiercn <[email protected]>

src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHost.cs

Co-authored-by: javiercn <[email protected]>

src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHost.cs

Co-authored-by: javiercn <[email protected]>

Initial plan

dfb448e

Copilot AI assigned Copilot and javiercn Sep 25, 2025

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dotnet-policy-service bot added the Attention: Shared Code Modified label Sep 25, 2025

Add hosted services support to WebAssemblyHost

9856ab7

Co-authored-by: javiercn <[email protected]>

Copilot AI changed the title ~~[WIP] Support hosted services in WebAssemblyHost~~ Support hosted services in WebAssemblyHost Sep 25, 2025

Copilot finished work on behalf of javiercn September 25, 2025 10:12

Copilot AI requested a review from javiercn September 25, 2025 10:12

This was referenced Sep 25, 2025

Known Build Error: error : Cannot create a file when that file already exists. #61178

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The active test run was aborted. Reason: Test host process crashed dotnet/dnceng#451

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javiercn marked this pull request as ready for review December 1, 2025 13:18

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Use LoggerMessage source generator pattern for error logging

d8752fb

Co-authored-by: javiercn <[email protected]>

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src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHost.cs Outdated Show resolved Hide resolved

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Encapsulate hosted service behavior in HostedServiceExecutor

d653850

Co-authored-by: javiercn <[email protected]>

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Copilot started work on behalf of javiercn December 12, 2025 15:15 View session

Register HostedServiceExecutor in DI and move error handling to executor

da2e4ed

Co-authored-by: javiercn <[email protected]>

Copilot AI requested a review from javiercn December 12, 2025 15:27

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javiercn removed the pending-ci-rerun When assigned to a PR indicates that the CI checks should be rerun label Dec 12, 2025

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javiercn merged commit 49a3054 into main Dec 15, 2025
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alexaka1 mentioned this pull request Dec 15, 2025

feat: Add optional Task support for BatchExportProcessor and PeriodicExportingMetricReader open-telemetry/opentelemetry-dotnet#6379

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[main] Source code updates from dotnet/aspnetcore dotnet/dotnet#3906

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Support hosted services in WebAssemblyHost #63814

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edited

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		var logger = Services.GetService<ILogger<WebAssemblyHost>>();
		logger?.LogError(ex, "An error occurred stopping hosted services during disposal.");

Support hosted services in WebAssemblyHost #63814

Support hosted services in WebAssemblyHost #63814

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Description

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Copilot AI commented Sep 25, 2025 •

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