Version: 2020.2

IJobFor

interface in Unity.Jobs

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描述

For 作业允许对原生容器的每个元素执行相同的独立操作,或者迭代固定的次数。 此作业类型为控制作业的调度提供了最灵活的方式。

该作业允许通过多种方式选择如何对工作进行调度。:

Run 会在主线程上运行作业并立即完成。

Schedule 会将作业调度到工作线程(或者可能是主线程)上运行,但是会指示工作应在单个线程中进行。 此选项允许在主线程之外完成工作,不过由于工作会按顺序执行,因此更易于推断。

ScheduleParallel 会调度作业到多个工作线程上同时运行。此调度选项可以提供最佳性能,但是需要用户了解,在从多个工作线程同时访问相同数据时可能发生的冲突。

Execute(int index) 会对每个索引(从 0 到提供的长度)执行一次。

Run 和 Schedule 会保证按顺序调用作业的 Execute(int index) 方法。

ScheduleParallel 不会提供这种保证,因为会从多个相互并行的工作线程中调用。 每个迭代必须独立于其他迭代(安全系统会强制执行此规则)。索引没有确定的顺序,而是在多个核心上并行执行。 Unity 会自动将工作拆分为不小于所提供 batchSize 的块,并根据工作线程数、数组长度和批次大小调度适当数量的作业。 批次大小通常应根据作业中执行的工作量来选择。简单作业(例如互相添加一些 Vector3)的批次大小应为 32 到 128。但是,如果执行的工作涉及十分高昂的成本,那么最好使用较小的批次大小;对于高成本工作,完全可以将批次大小设置为 1。IJobFor 使用原子操作执行工作窃取。批次大小可能较小,但仍有开销。

返回的 JobHandle 可用于确保作业已完成。它也可以作为依赖项传递给其他作业,从而确保作业在工作线程中逐个执行。

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

class ApplyVelocityParallelForSample : MonoBehaviour { struct VelocityJob : IJobFor { // Jobs declare all data that will be accessed in the job // By declaring it as read only, multiple jobs are allowed to access the data in parallel [ReadOnly] public NativeArray<Vector3> velocity;

// By default containers are assumed to be read &amp; write public NativeArray<Vector3> position;

// Delta time must be copied to the job since jobs generally don't have concept of a frame. // The main thread waits for the job same frame or next frame, but the job should do work deterministically // independent on when the job happens to run on the worker threads. public float deltaTime;

// The code actually running on the job public void Execute(int i) { // Move the positions based on delta time and velocity position[i] = position[i] + velocity[i] * deltaTime; } }

public void Update() { var position = new NativeArray<Vector3>(500, Allocator.Persistent);

var velocity = new NativeArray<Vector3>(500, Allocator.Persistent); for (var i = 0; i < velocity.Length; i++) velocity[i] = new Vector3(0, 10, 0);

// Initialize the job data var job = new VelocityJob() { deltaTime = Time.deltaTime, position = position, velocity = velocity };

// Schedule job to run immediately on main thread. First parameter is how many for-each iterations to perform. job.Run(position.Length);

// Schedule job to run at a later point on a single worker thread. // First parameter is how many for-each iterations to perform. // The second parameter is a JobHandle to use for this job's dependencies. // Dependencies are used to ensure that a job executes on worker threads after the dependency has completed execution. // In this case we don't need our job to depend on anything so we can use a default one. JobHandle sheduleJobDependency = new JobHandle(); JobHandle sheduleJobHandle = job.Schedule(position.Length, sheduleJobDependency);

// Schedule job to run on parallel worker threads. // First parameter is how many for-each iterations to perform. // The second parameter is the batch size, // essentially the no-overhead innerloop that just invokes Execute(i) in a loop. // When there is a lot of work in each iteration then a value of 1 can be sensible. // When there is very little work values of 32 or 64 can make sense. // The third parameter is a JobHandle to use for this job's dependencies. // Dependencies are used to ensure that a job executes on worker threads after the dependency has completed execution. JobHandle sheduleParralelJobHandle = job.ScheduleParallel(position.Length, 64, sheduleJobHandle);

// Ensure the job has completed. // It is not recommended to Complete a job immediately, // since that reduces the chance of having other jobs run in parallel with this one. // You optimally want to schedule a job early in a frame and then wait for it later in the frame. sheduleParralelJobHandle.Complete();

Debug.Log(job.position[0]);

// Native arrays must be disposed manually. position.Dispose(); velocity.Dispose(); } }

公共函数

Execute实现此方法以针对特定迭代索引执行工作。