AsyncTask

AsyncTask系统实现的多线程与自己实现继承的FRunnable实现的原理相似，还可以利用UE4提供的线程池。当使用多线程不满意时也可以调用StartSynchronousTask改成主线程执行。

来自头文件 AysncWork.h 文件中注释，直接仿照注释来实现AsyncTask

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FAutoDeleteAsyncTask - template task for jobs that delete themselves when complete

Sample code:

class ExampleAutoDeleteAsyncTask : public FNonAbandonableTask
{
    friend class FAutoDeleteAsyncTask<ExampleAutoDeleteAsyncTask>;

    int32 ExampleData;

    ExampleAutoDeleteAsyncTask(int32 InExampleData)
     : ExampleData(InExampleData)
    {
    }

    void DoWork()
    {
        ... do the work here
    }

    FORCEINLINE TStatId GetStatId() const
    {
        RETURN_QUICK_DECLARE_CYCLE_STAT(ExampleAutoDeleteAsyncTask, STATGROUP_ThreadPoolAsyncTasks);
    }
};


void Example()
{
    // start an example job
    (new FAutoDeleteAsyncTask<ExampleAutoDeleteAsyncTask>(5)->StartBackgroundTask();

    // do an example job now, on this thread
    (new FAutoDeleteAsyncTask<ExampleAutoDeleteAsyncTask>(5)->StartSynchronousTask();
}

代码实现：

继承FNonAbandonableTask创建一个线程类

在DoWork中实现需要实现的功能

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// FTestAsyncTask.h 
  #include "Async\AsyncWork.h"
  #include "CoreMinimal.h"

class MX_API FTestAsyncTask : public FNonAbandonableTask
{
public:
    friend class FAutoDeleteAsyncTask<FTestAsyncTask>;
    int32 RunCount = 0;

    FTestAsyncTask(FString ThreadName,class AActor1* a1) : MyThreadName(ThreadName), A1(a1) {};
    ~FTestAsyncTask();

    void DoWork();

    FORCEINLINE TStatId GetStatId() const
    {
        RETURN_QUICK_DECLARE_CYCLE_STAT(FTestAsyncTask, STATGROUP_ThreadPoolAsyncTasks);
    }

    FString MyThreadName;
    class AActor1* A1;
    static FCriticalSection CriticalSection;
};
///////////////////////////////////////////////////////////////////////
// FTestAsyncTask.cpp 
FCriticalSection FTestAsyncTask::CriticalSection;

FTestAsyncTask::~FTestAsyncTask()
{

}

void FTestAsyncTask::DoWork()
{
    UE_LOG(LogTemp, Log, TEXT("%s------%d"), *MyThreadName, RunCount);
    while (IsValid(A1)) {
        // 同步锁
        FScopeLock Lock(&CriticalSection);
        if (A1->TestCount < A1->TestTarget)
        {
            A1->TestCount++;
            RunCount++;
            // 节约资源 每100次打印一次
            if (RunCount % 100 == 0)
                UE_LOG(LogTemp, Log, TEXT("%s======%d"), *MyThreadName, RunCount);
        }
        else
        {
            break;
        }
    }
    
}

执行线程类：

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// 头文件
    int32 TestCount;

    UPROPERTY(EditAnywhere)
        int32 TestTarget;
// 线程运行
    (new FAutoDeleteAsyncTask<FTestAsyncTask>("thread1", this))->StartBackgroundTask();
    (new FAutoDeleteAsyncTask<FTestAsyncTask>("thread2", this))->StartBackgroundTask();

在自定义执行的线程类中 使用 FAutoDeleteAsyncTask 来传入我们刚才写的Task。FAutoDeleteAsyncTask顾名思义就是任务执行完就会自动删除。

还有StartBackgroundTask和StartSynchronousTask的区别：

  • StartBackgroundTask会利用线程池里空闲的线程来执行。
  • StartSynchronousTask则是主线程执行。

执行结果：

LogTemp: thread2======30600
LogTemp: thread1======68000
LogTemp: thread1======68100
LogTemp: thread2======30700
LogTemp: thread2======30800
LogTemp: thread1======68200
LogTemp: thread1======68300
LogTemp: thread2======30900
LogTemp: thread2======31000
LogTemp: thread1======68400
LogTemp: thread1======68500
LogTemp: thread1======68600
LogTemp: thread1======68700
LogTemp: thread1======68800
LogTemp: thread2======31100
PIE: Play in editor total start time 0.055

这里运行次数设置的为100000 缺少一次是因为当满足条件是直接跳出了，没有打印出