# Burst compilation in Play mode


When you create a [build of your project](/engine/6000.6/manual/building-and-publishing.md), Burst compiles all the supported code ahead-of-time (AOT) into a native library which Unity ships with your application.

When previewing your application in the Editor's Play mode, Burst provides the following compilation modes:

* Asynchronous: Parts of your code marked for Burst compilation can run as managed, just-in-time (JIT) compiled code in the .NET runtime while waiting for Burst compilation to complete. This is the default behavior.
* Synchronous: Parts of your code marked for Burst compilation can only run as Burst-compiled native code and your application must wait for Burst compilation to complete.

## Synchronous compilation

To force synchronous compilation in Play mode, set the [`CompileSynchronously`](/engine/6000.6/script-reference/unity/burst/burstcompileattribute/compilesynchronously.md) property to `true` as follows:

```lang-cs
[BurstCompile(CompileSynchronously = true)]
public struct MyJob : IJob
{
    // ...
}
```

Waiting for synchronous compilation affects the current running frame, which can cause hitches and make your application unresponsive. Synchronous compilation is only recommended in the following situations:

* If you have a long running job that only runs once. The performance of the compiled code might outweigh the downsides of synchronous compilation.
* If you're profiling a Burst job and want to test the code from the Burst compiler. When you do this, perform a warmup to discard any timing measurements from the first call to the job. This is because the profiling data includes the compilation time and skews the result.
* To aid with debugging the difference between managed and Burst compiled code.

## Additional resources

* [Marking code for Burst compilation](/engine/6000.6/manual/scripting/compilation-and-code-reload/script-compilation/burst/compilation/burstcompile.md)
* [Generic jobs](/engine/6000.6/manual/scripting/compilation-and-code-reload/script-compilation/burst/compilation/generic-jobs.md)