c++ - 多线程返回未处理的异常用于存储信息

Question

我会尽可能清楚地解释我的问题。我有一个必须处理的多线程框架。这是一个路径跟踪器渲染器。当我尝试存储我的线程提供的一些信息时，它给了我错误。为了避免发布所有代码，我将逐步解释我的意思:

我的 TileTracer 类是一个线程

class TileTracer : public Thread{
...
}

我有一定数量的线程:

#define MAXTHREADS      32
TileTracer* worker[MAXTHREADS];

在下面的初始化代码中设置了工作线程数，这里也启动了线程:

void Renderer::Init(){
    accumulator = (vec3*)MALLOC64(sizeof(vec3)* SCRWIDTH * SCRHEIGHT);
    memset(accumulator, 0, SCRWIDTH * SCRHEIGHT * sizeof(vec3));
    SYSTEM_INFO systeminfo;
    GetSystemInfo(&systeminfo);
    int cores = systeminfo.dwNumberOfProcessors;
    workerCount = MIN(MAXTHREADS, cores);
    for (int i = 0; i < workerCount; i++)
    {
        goSignal[i] = CreateEvent(NULL, FALSE, FALSE, 0);
        doneSignal[i] = CreateEvent(NULL, FALSE, FALSE, 0);
    }
    // create and start worker threads
    for (int i = 0; i < workerCount; i++)
    {
         worker[i] = new TileTracer();
         worker[i]->init(accumulator, i);
         worker[i]->start(); //start the thread
    }
    samples = 0;
}

我的线程的 init() 方法在我的 header 中简单定义如下:

void init(vec3* target, int idx) { accumulator = target, threadIdx = idx; }

当 start() 是:

void Thread::start() 
{
     DWORD tid = 0; 
     m_hThread = (unsigned long*)CreateThread( NULL, 0,    (LPTHREAD_START_ROUTINE)sthread_proc, (Thread*)this, 0, &tid );
     setPriority( Thread::P_NORMAL );
 }

不知何故(我不知 Prop 体在哪里)，每个线程调用以下主要方法，该方法用于定义像素的颜色(您不必全部理解):

vec3 TileTracer::Sample(vec3 O, vec3 D, int depth){
  vec3 color(0, 0, 0);
  // trace path extension ray
  float t = 1000.0f, u, v;
  Triangle* tri = 0;
  Scene::mbvh->pool4[0].TraceEmbree(O, D, t, u, v, tri, false);
  totalRays++;
  // handle intersection, if any
  if (tri)
  {
    // determine material color at intersection point
    Material* mat = Scene::matList[tri->material];
    Texture* tex = mat->GetTexture();
    vec3 diffuse;
    if (tex)
    {
        ...
    }
    else diffuse = mat->GetColor();
    vec3 I = O + t * D; //we get exactly to the intersection point on the object

    //we need to store the info of each bounce of the basePath for the offsetPaths
    basePath baseInfo = { O, D, I, tri };
    basePathHits.push_back(baseInfo);

    vec3 L = vec3(-1 + Rand(2.0f), 20, 9 + Rand(2.0f)) - I; //(-1,20,9) is Hard-code of the light position, and I add Rand(2.0f) on X and Z axis
    //so that I have an area light instead of a point light
    float dist = length(L) * 0.99f; //if I cast a ray towards the light source I don't want to hit the source point or the light source
    //otherwise it counts as a shadow even if there is not. So I make the ray a bit shorter by multiplying it for 0.99
    L = normalize(L);
    float ndotl = dot(tri->N, L);
    if (ndotl > 0)
    {
        Triangle* tri = 0;
        totalRays++;
        Scene::mbvh->pool4[0].TraceEmbree(I + L * EPSILON, L, dist, u, v, tri, true);//it just calculates the distance by throwing a ray
        //I am just interested in understanding if I hit something or not
        //if I don't hit anything I calculate the light transport (diffuse * ndotL * lightBrightness * 1/dist^2
        if (!tri) color += diffuse * ndotl * vec3(1000.0f, 1000.0f, 850.0f) * (1.0f / (dist * dist));
    }
    // continue random walk since it is a path tracer (we do it only if we have less than 20 bounces)
    if (depth < 20)
    {
        // russian roulette
        float Psurvival = CLAMP((diffuse.r + diffuse.g + diffuse.b) * 0.33333f, 0.2f, 0.8f);
        if (Rand(1.0f) < Psurvival)
        {
            vec3 R = DiffuseReflectionCosineWeighted(tri->N);//there is weight
            color += diffuse * Sample(I + R * EPSILON, R, depth + 1) * (1.0f / Psurvival);
        }
    }
  }
  return color;
}

现在，您不必完全理解整个代码，因为我的问题如下:如果您注意到，在最后一个方法中有以下 2 行代码:

basePath baseInfo = { O, D, I, tri };
basePathHits.push_back(baseInfo);

我只是创建了一个简单的结构“basePath”，定义如下:

struct basePath
{
    vec3 O, D, hit;
    Triangle* tri;
};

然后我将它存储在代码开头定义的结构 vector 中:

vector<basePath> basePathHits;

问题是这似乎带来了一个异常(exception)。事实上，如果我尝试存储这些信息，我稍后需要在我的代码中使用，程序会崩溃并给出异常:

Template.exe 中 0x0FD4FAC1 (msvcr120d.dll) 处的未处理异常:0xC0000005:访问冲突读取位置 0x3F4C1BC1。

其他时候，不做任何更改，错误是不同的，如下所示:

虽然没有存储这些信息，但一切都完美无缺。同样，如果我将核心数设置为 1，一切正常。那么，为什么多线程不允许我这样做呢？如果这些还不够，请不要犹豫，询问更多信息。

Answer 1

尝试对您的代码进行以下更改:

//we need to store the info of each bounce of the basePath for the offsetPaths
basePath baseInfo = { O, D, I, tri }; 
static std::mutex myMutex;
myMutex.lock();
basePathHits.push_back(baseInfo);
myMutex.unlock();

如果这消除了异常，那么问题是对 basePathHits 的非同步访问(即多个线程同时调用 push_back)。您需要仔细考虑最好的解决方案是什么，以尽量减少同步对性能的影响。