.NET API support on the Web platform

Understand the limitations of .NET APIs on the Web platform, including unsupported namespaces and alternatives.

Read time 4 minutes

Last updated 12 days ago

The Web platform supports most of the .NET API, but some APIs have limitations due to browser security restrictions, the absence of managed threading, and the lack of raw network socket access.

System.Collections.Concurrent

All containers in

System.Collections.Concurrent

compile on the Web platform, but they lack real thread safety. Unity replaces the synchronization primitives in these containers with empty functions. Use the Collections package as an alternative for Burst-compiled jobs.

System.IO

Most file I/O works through Emscripten's in-memory virtual file system (MEMFS). Asynchronous I/O APIs don't work because they are backed by the

ThreadPool

. The following table lists the APIs with limitations.

Class	Status	Notes
DriveInfo	Not supported	All methods throw `NotSupportedException` .
FileStream	Partially supported	All synchronous operations work. Async methods cause an unrecoverable browser hang.
FileSystemAclExtensions	Not supported	Windows-only. All methods throw `NotSupportedException` .

System.Threading

Because the Web platform doesn't support managed threading, most APIs in this namespace have limited functionality. Synchronization primitives compile and execute without throwing, but their threading behavior has no effect. The only exceptions are

Interlocked

Thread.MemoryBarrier

and

Volatile

, which provide real hardware semantics inside Burst-compiled jobs.

The following table lists the APIs with limitations.

Class	Status	Notes
CancellationTokenSource	Partially supported	The timeout mechanism doesn't work because it relies on `Timer` .
CompressedStack	Not supported	All methods throw `NotSupportedException` .
EventWaitHandle	Not supported	Named event handles throw `NotSupportedException` . Other methods execute but have no effect.
HostExecutionContextManager	Not supported	All methods throw `NotImplementedException` .
Interlocked	Partially supported	The method executes without effect in managed code, but provides real hardware semantics inside Burst-compiled jobs.
Monitor	Not supported	Other methods execute but have no effect.
Mutex	Not supported	Named mutexes throw `NotSupportedException` . Other methods execute but have no effect.
Semaphore	Not supported	Named semaphores throw `NotSupportedException` . Other methods execute but have no effect.
Thread	Not supported	Can be constructed. `Start()` doesn't throw, but thread delegates don't execute. `Join` , `Priority` (set), and `DisableComObjectEagerCleanup` fail.
Thread.MemoryBarrier	Partially supported	The method executes without effect in managed code, but provides real hardware semantics inside Burst-compiled jobs.
ThreadPool	Not supported	`QueueUserWorkItem` and `UnsafeQueueUserWorkItem` accept calls but callbacks never execute.
Timer	Not supported	Doesn't work because it relies on `ThreadPool` .
Volatile	Partially supported	The method executes without effect in managed code, but provides real hardware semantics inside Burst-compiled jobs.

System.Threading.Tasks

The following types and methods in the

System.Threading.Tasks

namespace function correctly:

```
ValueTask
```
```
ValueTask<T>
```
```
TaskCompletionSource<T>
```
Synchronous factory methods such as
```
Task.FromResult
```
and
```
Task.CompletedTask
```
.

All APIs that schedule work through the

ThreadPool

cause an unrecoverable browser hang. Use

Awaitable

for asynchronous programming because it has lower memory overhead than

Task

The following table lists the APIs with limitations.

Class	Status	Notes
Parallel	Not supported	All methods ( `For` , `ForEach` , `Invoke` ) cause an unrecoverable browser hang.
Task.Delay	Not supported	Causes an unrecoverable browser hang. The internal timer doesn't fire.
Task.Run	Not supported	Causes an unrecoverable browser hang. Schedules work through `ThreadPool` .
TaskFactory / TaskFactory<T>	Not supported	`StartNew` , `ContinueWhenAll` , and `ContinueWhenAny` all cause an unrecoverable browser hang.

System.Timers

System.Timers.Timer

doesn't work on the Web platform because the

Elapsed

event relies on the thread pool mechanism, which doesn't function.

System.Net and System.Net.Http

The following data classes in the

System.Net

and

System.Net.Http

namespaces function correctly:

```
Cookie
```
```
WebHeaderCollection
```
```
SocketAddress
```
```
HttpRequestMessage
```
```
StringContent
```
```
MultipartContent
```

HttpListener

isn't supported because it isn't possible to run a web server inside a browser.

The following classes aren't implemented and cause an unrecoverable browser hang:

```
HttpClient
```
```
WebClient
```
```
HttpWebRequest
```
```
FileWebRequest
```

Use UnityWebRequest as an alternative for HTTP requests.

System.Net.Security

SslStream

and

NegotiateStream

aren't supported. Configuration option classes work.

System.Net.Sockets

The browser sandbox doesn't expose POSIX sockets. Only pure data types such as

LingerOption

and

SocketException

work.

As an alternative, use the browser's WebSocket or WebRTC APIs through a JavaScript plug-in. Another option is the Emscripten POSIX socket implementation, which proxies socket operations through a WebSocket-based relay server to connect to real socket ports on non-web clients or servers.

System.Net.WebSockets

ClientWebSocket

isn't supported. Use the browser's WebSocket API directly through a JavaScript plug-in or a third-party plug-in.

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.NET API support on the Web platform

System.Collections.Concurrent

System.IO

Class

Status

Notes

System.Threading

Class

Status

Notes

System.Threading.Tasks

Class

Status

Notes

System.Timers

System.Net and System.Net.Http

System.Net.Security

System.Net.Sockets

System.Net.WebSockets

Additional resources