Bug in hdf5open.c::get_quantize_info()

[uweschulzweida]

I get the following error messages since netCDF-c version 4.9.0:

   ...
  #000: H5A.c line 545 in H5Aopen_by_name(): can't open attribute
  #001: H5VLcallback.c line 1128 in H5VL_attr_open(): attribute open failed
  #002: H5VLcallback.c line 1095 in H5VL__attr_open(): attribute open failed
  #003: H5VLnative_attr.c line 132 in H5VL__native_attr_open(): can't open attribute
  #004: H5Aint.c line 559 in H5A__open_by_name(): unable to load attribute info from object header
  #005: H5Oattribute.c line 508 in H5O__attr_open_by_name(): can't locate attribute: '_QuantizeBitGroomNumberOfSignificantDigits'
   …
  #005: H5Oattribute.c line 508 in H5O__attr_open_by_name(): can't locate attribute: ‚_QuantizeGranularBitRoundNumberOfSignificantDigits'
  ...
  #005: H5Oattribute.c line 508 in H5O__attr_open_by_name(): can't locate attribute: '_QuantizeBitRoundNumberOfSignificantBits'

I think in routine hdf5open.c::get_quantize_info() the corresponding calls to H5Aexists() are missing.
I have added the following lines:

attr_exists = H5Aexists(datasetid, NC_QUANTIZE_BITGROOM_ATT_NAME);
attr_exists = H5Aexists(datasetid, NC_QUANTIZE_GRANULARBR_ATT_NAME);
attr_exists = H5Aexists(datasetid, NC_QUANTIZE_BITROUND_ATT_NAME);

With these calls I don't get any error messages anymore.

The problem occurs when opening NetCDF4 files in a multi-threaded environment when calling the routine nc_inq_var().
In the following C++ example, 2 files are opened in parallel and both threads are locked with a unique_lock:

#include "netcdf.h"
#include <cstdio>
#include <cstdlib>
#include <thread>
#include <mutex>

static std::mutex openMutex;

static void nce(int istat)
{
  if (istat != NC_NOERR)
    {
      fprintf(stderr, "%s\n", nc_strerror(istat));
      exit(-1);
    }
}

static int open_file(const char *filename)
{
  std::unique_lock<std::mutex> lockedMutex(openMutex);

  int ncid;
  nce(nc_open(filename, NC_NOWRITE, &ncid));

  int ndims, nvars, ngatts, unlimdimid;
  nc_inq(ncid, &ndims, &nvars, &ngatts, &unlimdimid);
  for (int varid = 0; varid < nvars; ++varid)
    {
      nc_type xtype;
      int nvdims, nvatts, dimids[9];
      nc_inq_var(ncid, varid, NULL, &xtype, &nvdims, dimids, &nvatts);
    }

  return ncid;
}

static void close_file(int ncid)
{
  nce(nc_close(ncid));
}

static void read_file(const char *filename)
{
  int ncid = open_file(filename);
  close_file(ncid);
}

int main(void)
{
  std::thread t1(read_file, "ifile1.nc");
  std::thread t2(read_file, "ifile2.nc");

  t1.join();
  t2.join();

  return 0;
}