pmpi_gather致命錯誤

Question

所以我有一個我正在編寫的raytracer編譯就好了，但是當我到達MPI_Gather（）函數時，我得到了這個錯誤集。如果我寫入文件，整個事情都會很好，但是我不能在分佈式計算系統上運行它。

Fatal error in PMPI_Gather: Internal MPI error!, error stack: 
PMPI_Gather(856)......: 
    MPI_Gather(sbuf=0x8e05468, scount=882000, MPI_BYTE, rbuf=0x8df7628, rcount=882000, MPI_BYTE, root=0, MPI_COMM_WORLD) failed 
MPIR_Gather_impl(681).: 
MPIR_Gather(641)......: 
MPIR_Gather_intra(152): 
MPIR_Localcopy(378)...: 
    memcpy arguments alias each other, dst=0x8df7628 src=0x8e05468 len=882000 

=================================================================================== 
= BAD TERMINATION OF ONE OF YOUR APPLICATION PROCESSES 
= EXIT CODE: 1 
= CLEANING UP REMAINING PROCESSES 
= YOU CAN IGNORE THE BELOW CLEANUP MESSAGES 
=================================================================================== 

我不完全確定這個錯誤是什麼意思，所以很難繞過它。

下面是主要功能源：

int main(int argc, char **argv) { 
    clock_t total_time = clock(), otime; 
    init_MPI(argc, argv); //Initialize OpenMPI 
    glutInit(&argc,argv); 

    get_params(argc, argv); //Get parameters from command line 
    if (buildScene(scene, cam) == -1) MPI_Abort(MPI_COMM_WORLD,rc); exit(1); 
    samples = samples > 0 ? whitted ? 1 : samples : 1; 
    if (numprocs == 1) { 
    scn = new RGBApixmap(h,w); 
    raytrace(h,scn); 
    if (smult > 1) *scn = scaleImage(scn,smult); 
    } else { 
    int rows = h/numprocs; 
    subscn = new RGBApixmap(rows,w); 
    raytrace(rows, subscn); 
    if (smult > 1) *subscn = scaleImage(subscn,smult); 

    if (pid == MASTER) scn = new RGBApixmap(h/smult,w/smult); 
    MPI_Gather(subscn,rows/smult*w,MPI_BYTE,scn,rows/smult*w,MPI_BYTE,MASTER,MPI_COMM_WORLD); 
    } 
    if (pid == MASTER) { 
    initGlut(argc, argv); 
    glutMainLoop(); 
    } 
    MPI_Finalize(); 
    return 0; 
} 

編輯：

我已經解決了問題，下面貼更新的代碼：

int main(int argc, char **argv) { 
    clock_t total_time = clock(), otime; 
    init_MPI(argc, argv); 
    glutInit(&argc,argv);  
    bool OK = get_params(argc, argv); 
    if (buildScene(scene, cam) == -1) { MPI_Abort(MPI_COMM_WORLD,rc); exit(1); } 
    samples = samples > 0 ? whitted ? 1 : samples : 1; 
    int rows = h/numprocs; 
    subscn = new RGBApixmap(rows,w); 
    raytrace(rows, subscn); 
    MPI_Barrier(MPI_COMM_WORLD);   /* Synchronize all processes */ 
    if (smult > 1) *subscn = scaleImage(subscn,smult); 
    MPI_Barrier(MPI_COMM_WORLD);   /* Synchronize all processes */ 

    int nElts = subscn->getWidth()*subscn->getHeight(); 
    RGBA *subscnpix, *scnpix; 
    subscnpix = subscn->getPixs(); 
    scnpix = (RGBA*)malloc(sizeof(RGBA)*((w/smult)*(h/smult))); 

    MPI_Datatype pixel; 
    MPI_Type_contiguous(4,MPI_UNSIGNED_CHAR,&pixel); 
    MPI_Type_commit(&pixel); 

    MPI_Gather(subscnpix,nElts,pixel,scnpix,nElts,pixel,MASTER,MPI_COMM_WORLD); 

    scn = new RGBApixmap(h/smult,w/smult,scnpix); 

    MPI_Type_free(&pixel); 

    MPI_Barrier(MPI_COMM_WORLD);   /* Synchonize all processes */ 
    if (pid == MASTER) { 
    initGlut(argc, argv); 
    glutMainLoop(); 
    } 
    MPI_Finalize(); 
    return 0; 
} 

Answer 1

您的發送和接收緩衝區在撥打MPI_Gather的排名MASTER重疊，這是違反MPI標準強加的限制。 subscn位於0x8e05468，而scn位於0x8df7628。從0x8df7628到0x8e05468的內存範圍僅爲56896字節，而您正試圖向其寫入882000次numprocs字節，這將不起作用。

這是由於您將行數除以縮放因子但仍忘記將圖像寬度w除以縮放因子。

MPI_Gather(subscn, rows/smult*w/smult, MPI_BYTE, 
      scn, rows/smult*w/smult, MPI_BYTE, 
      MASTER, MPI_COMM_WORLD); 

注意，如果象素圖是不是灰度，也不得不通過顏色分量的數目（可能計數alpha通道太）相乘的數據元素的數量或創建一個連續的派生數據類型來代替。