Hello,
I seem to have encountered a bug in MPI-IO, in which
MPI_File_get_position_shared hangs when called by multiple processes in
a communicator. It can be illustrated by the following simple test case,
in which a file is simply created with C IO, and opened with MPI-IO.
(defining or undefining MY_MPI_IO_BUG on line 5 enables/disables the
bug). From the MPI2 documentation, It seems that all processes should be
able to call MPI_File_get_position_shared, but if more than one process
uses it, it fails. Setting the shared pointer helps, but this should not
be necessary, and the code still hangs (in more complete code, after
writing data).
I encounter the same problem with Open MPI 1.2.6 and MPICH2 1.0.7, so
I may have misread the documentation, but I suspect a ROMIO bug.
Best regards,
Yvan Fournier
/*============================================================================
* Parallel file I/O shared pointer bug test
*============================================================================*/
#define MY_MPI_IO_BUG 1
/*----------------------------------------------------------------------------
* Standard C library headers
*----------------------------------------------------------------------------*/
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <mpi.h>
/*----------------------------------------------------------------------------*/
#ifdef __cplusplus
extern "C" {
#if 0
} /* Fake brace to force Emacs auto-indentation back to column 0 */
#endif
#endif /* __cplusplus */
/*============================================================================
* Private function definitions
*============================================================================*/
/*----------------------------------------------------------------------------
* Output MPI error message.
*
* This supposes that the default MPI errorhandler is not used
*
* parameters:
* error_code <-- associated MPI error code
*
* returns:
* 0 in case of success, system error code in case of failure
*----------------------------------------------------------------------------*/
static void
_mpi_io_error_message(int error_code)
{
char buffer[MPI_MAX_ERROR_STRING];
int buffer_len;
MPI_Error_string(error_code, buffer, &buffer_len);
printf("MPI IO error %d: %s", error_code, buffer);
}
/*----------------------------------------------------------------------------
* Return the position of the file pointer.
*
* When using MPI-IO with individual file pointers, we consider the file
* pointer to be equal to the highest value of then individual file pointers.
*
* parameters:
* fh <-- MPI IO file descriptor
*
* returns:
* current position of the file pointer
*----------------------------------------------------------------------------*/
MPI_Offset
_mpi_file_tell(MPI_File fh)
{
int errcode = MPI_SUCCESS;
MPI_Offset offset = 0, disp = 0, retval = 0;
int rank;
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
#if defined(MY_MPI_IO_BUG)
printf("rank %d: will call MPI_File_get_position_shared\n", rank);
errcode = MPI_File_get_position_shared(fh, &offset);
if (errcode == MPI_SUCCESS) {
MPI_File_get_byte_offset(fh, offset, &disp);
retval = disp;
}
printf("rank %d: offsets: %ld %ld\n", rank, (long)offset, (long)disp);
#else
long aux[2];
if (rank == 0) {
printf("root rank will call MPI_File_get_position_shared\n");
errcode = MPI_File_get_position_shared(fh, &offset);
if (errcode == MPI_SUCCESS) {
MPI_File_get_byte_offset(fh, offset, &disp);
retval = disp;
}
aux[0] = disp; aux[1] = retval;
}
MPI_Bcast(aux, 2, MPI_LONG, 0, MPI_COMM_WORLD);
disp = aux[0];
retval = aux[1];
printf("rank %d: offsets: %ld %ld\n", rank, (long)offset, (long)disp);
#endif
if (errcode != MPI_SUCCESS)
_mpi_io_error_message(errcode);
return retval;
}
/*============================================================================
* Unit test
*============================================================================*/
static void
_create_test_data(void)
{
int i;
FILE *f;
char header[80];
char footer[80];
sprintf(header, "fvm test file");
for (i = strlen(header); i < 80; i++)
header[i] = '\0';
sprintf(footer, "fvm test file end");
for (i = strlen(footer); i < 80; i++)
footer[i] = '\0';
f = fopen("file_test_data", "w+");
fwrite(header, 1, 80, f);
fwrite(footer, 1, 80, f);
fclose(f);
}
/*---------------------------------------------------------------------------*/
int
main (int argc, char *argv[])
{
int rank = 0;
int retval = MPI_SUCCESS;
MPI_Offset offset;
MPI_File fh = MPI_FILE_NULL;
/* Initialization */
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
if (rank == 0)
_create_test_data();
/* Open file */
retval = MPI_File_open(MPI_COMM_WORLD,
"file_test_data",
MPI_MODE_RDONLY,
MPI_INFO_NULL,
&fh);
if (retval != MPI_SUCCESS)
_mpi_io_error_message(retval);
#if 0 /* Hides the bug, but does not make it dissapear in more
complex cases (i.e. when MPI_File_read_shared is used
locally and MPI_File_read_ordered is used collectively) */
retval = MPI_File_seek_shared(fh, 1, MPI_SEEK_SET);
if (retval != MPI_SUCCESS)
_mpi_io_error_message(retval);
#endif
offset = _mpi_file_tell(fh);
/* Close file */
retval = MPI_File_close(&fh);
if (retval != MPI_SUCCESS)
_mpi_io_error_message(retval);
/* We are finished */
MPI_Finalize();
exit(EXIT_SUCCESS);
}
