ReadOnlyAttribute

Description

The ReadOnly attribute lets you mark a member of a struct used in a job as read-only.

Native containers are read-write by default when used in a job. This means that you cannot schedule two jobs referencing the same containers simultaneously. By adding the [ReadOnly] attribute to the container field in the job struct the container is marked as read-only, which allows two jobs to run in parallel reading data from the same container.

See Also: IJob, IJobParallelFor.

using Unity.Jobs;
using Unity.Collections;
using UnityEngine;

public struct MyJob : IJob
{
    [ReadOnly]
    public NativeArray<int> input;

    public NativeArray<int> output;

    public void Execute()
    {
        for (var i = 0; i < output.Length; ++i)
            output[i] = input[i];
    }
}

public class ParallelReplicator : MonoBehaviour
{
    public void OnUpdate()
    {
        const int n = 10000;
        var original = new NativeArray<int>(n, Allocator.Persistent);
        var clone1 = new NativeArray<int>(n, Allocator.Persistent);
        var clone2 = new NativeArray<int>(n, Allocator.Persistent);

        var job1 = new MyJob
        {
            input = original,
            output = clone1
        };
        var job2 = new MyJob
        {
            input = original,
            output = clone2
        };

        var jobX = new MyJob
        {
            input = original,
            output = clone2
        };

        // Run the jobs in parallel.
        var jobs = JobHandle.CombineDependencies(job1.Schedule(), job2.Schedule());

        // jobX.Schedule(); // Not allowed, throws exception because job2 is writing into copy2.

        jobs.Complete();

        jobX.Schedule().Complete(); // Allowed, because job2 has been completed by now.

        original.Dispose();
        clone1.Dispose();
        clone2.Dispose();
    }
}