OpenSlide segmentation faults in Windows

[Agelos Pappas]

Hi,

as I've reported in another message OpenSlide crashes reporting 
segmentation faults when running in a windows multi-threaded 
application. The problem occurs with any slide format, but is easier to 
reproduce with MIRAX files. I have been able to reproduce the problem in 
both x86 and x64 versions of OpenSlide by writing an application that 
spawns N threads which read AxA tiles starting from the top level and 
walking to the bottom. The application doesn't always crash and when it 
does, it is not at the same point.

The following (C++) function, if spawned in multiple threads (4 seem to 
be enough for me) will make the application crash reporting access 
violation:

DWORD WINAPI SlideWalk(LPVOID lpParam)
{
     const int TileSize = 256;
     __int64 w, h;

     int *osr = openslide_open(PATH_TO_SLIDE);
     int numLevels = openslide_get_level_count(osr);

     for (int i = numLevels - 1; i >= 0; i--)
     {
         openslide_get_level_dimensions(osr, i, &w, &h);
         double d = openslide_get_level_downsample(osr, i);

         for (int y = 0; y < h; y += TileSize)
         {
             for (int x = 0; x < w; x += TileSize)
             {
                 unsigned int *buffer = new unsigned int[TileSize * 
TileSize];
                 openslide_read_region(osr, buffer, floorl(x * d), 
floorl(y * d), i, TileSize, TileSize);
                 delete []buffer;
             }
         }
     }
     openslide_close(osr);
     return 0;
}

The above is just a quick test compiled under windows. I ran it using 
gdb in Cygwin and I got errors like these:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 7396.0x1e00]
sse2_composite_src_x888_8888 (imp=0x563c08, info=0xbbe22c) at 
pixman-sse2.c:2860
         in pixman-sse2.c

In all my tests the segmentation fault happens in libpixman, but not 
always at the same line.
I've written a similar program in Linux but it doesn't seem to crash, 
even though valgrind reported some errors in libpixman too.

Can someone test the attached C program in Linux using a public MRXS 
slide to see if they get any seg faults?

Regards
Pappas Agelos

-------------- next part --------------
#include <stdint.h>
#include <math.h>
#include <stdio.h>
#include <glib.h>
#include <openslide.h>

#define NTHREADS 4
#define TILE_SIZE 256

int thread_function(void *data)
{
  printf("%x thread started\n", (uint32_t)g_thread_self());

  int64_t x, y, w, h;
  uint32_t *buffer;
  openslide_t *osr = openslide_open((char *)data);

  if (osr == NULL) {
    printf("%s: Not a file that OpenSlide can recognize", (char *)data);
    return -1;
  }

  int numLevels = openslide_get_level_count(osr);

  for (int i = numLevels - 1; i >= 0; i--)
  {
    openslide_get_level_dimensions(osr, i, &w, &h);
    double d = openslide_get_level_downsample(osr, i);

    for (int y = 0; y < h; y += TILE_SIZE)
    {
      for (int x = 0; x < w; x += TILE_SIZE)
      {
        uint32_t *buffer = g_malloc(TILE_SIZE * TILE_SIZE * 4);
        openslide_read_region(osr, buffer, llround (x * d), llround (y * d), i, TILE_SIZE, TILE_SIZE);
        g_free(buffer);
      }
    }
  }

  openslide_close(osr);
  printf("%x thread stopping\n", (uint32_t)g_thread_self());

  return 0;
}

int main (int argc, char *argv[])
{
  int i;
  GThread *thread[NTHREADS];
  char *thread_names[NTHREADS];

  if (argc != 2) {
    printf("Slide file not supplied\n");
    return -1;
  }

  for (i=0; i<NTHREADS; i++) {
    thread_names[i] = g_malloc(256);
    sprintf(thread_names[i], "Thread %d", i);
    thread[i] = g_thread_new(thread_names[i], (GThreadFunc)thread_function, argv[1]);
  }

  for(i=0; i<NTHREADS; i++) {
    g_thread_join(thread[i]);
    g_free(thread_names[i]);
  }

  return 0;
}