Give an explicit error message if MPI can't be called from a sub-process

pytest_parallel/exception.py

@@ -0,0 +1,18 @@
+
+def _to_bold_red(s):
+  red = '\x1b[31m'
+  bold = '\x1b[1m'
+  reset = '\x1b[0m'
+  return red + bold + s + reset
+
+class PytestParallelInternalError(Exception):
+  def __init__(self, msg):
+    Exception.__init__(self, _to_bold_red('pytest_parallel internal error')+'\n' + msg)
+
+class PytestParallelUsageError(Exception):
+  def __init__(self, msg):
+    Exception.__init__(self, _to_bold_red('You are calling pytest_parallel incorrectly')+'\n' + msg)
+
+class PytestParallelEnvError(Exception):
+  def __init__(self, msg):
+    Exception.__init__(self, _to_bold_red('pytest_parallel environment error:')+'\n' + msg)

pytest_parallel/plugin.py

@@ -11,8 +11,7 @@
 import pytest
 from _pytest.terminal import TerminalReporter
 
-class PytestParallelError(ValueError):
-    pass
+from .exception import PytestParallelUsageError, PytestParallelInternalError
 
 # --------------------------------------------------------------------------
 def pytest_addoption(parser):
@@ -58,13 +57,13 @@ def pytest_addoption(parser):
                                                 ' (because importing mpi4py.MPI makes the current process look like and MPI process,' \
                                                 ' and SLURM does not like that)'
         if os.getenv('I_MPI_MPIRUN') is not None:
-            err_msg =  'Internal pytest_parallel error: the environment variable I_MPI_MPIRUN is set' \
+            err_msg =  'The environment variable I_MPI_MPIRUN is set' \
                       f' (it has value "{os.getenv("I_MPI_MPIRUN")}"),\n' \
                        ' while pytest was invoked with "--scheduler=slurm".\n' \
                        ' This indicates that pytest was run through MPI, and SLURM generally does not like that.\n' \
                        ' With "--scheduler=slurm", just run `pytest` directly, not through `mpirun/mpiexec/srun`,\n' \
                        ' because it will launch MPI itself (you may want to use --n-workers=<number of processes>).'
-            raise PytestParallelError(err_msg)
+            raise PytestParallelInternalError(err_msg)
 
         r = subprocess.run(['env','--null'], stdout=subprocess.PIPE) # `--null`: end each output line with NUL, required by `sbatch --export-file`
 
@@ -109,41 +108,41 @@ def pytest_configure(config):
         assert not is_worker, f'Internal pytest_parallel error `--_worker` not available with`--scheduler={scheduler}`'
     if scheduler in ['slurm', 'shell'] and not is_worker:
         if n_workers is None:
-            raise PytestParallelError(f'You need to specify `--n-workers` when `--scheduler={scheduler}`')
+            raise PytestParallelUsageError(f'You need to specify `--n-workers` when `--scheduler={scheduler}`')
     if scheduler != 'slurm':
         if slurm_options is not None:
-            raise PytestParallelError('Option `--slurm-options` only available when `--scheduler=slurm`')
+            raise PytestParallelUsageError('Option `--slurm-options` only available when `--scheduler=slurm`')
         if slurm_srun_options is not None:
-            raise PytestParallelError('Option `--slurms-run-options` only available when `--scheduler=slurm`')
+            raise PytestParallelUsageError('Option `--slurms-run-options` only available when `--scheduler=slurm`')
         if slurm_init_cmds is not None:
-            raise PytestParallelError('Option `--slurm-init-cmds` only available when `--scheduler=slurm`')
+            raise PytestParallelUsageError('Option `--slurm-init-cmds` only available when `--scheduler=slurm`')
         if slurm_file is not None:
-            raise PytestParallelError('Option `--slurm-file` only available when `--scheduler=slurm`')
+            raise PytestParallelUsageError('Option `--slurm-file` only available when `--scheduler=slurm`')
 
     if scheduler in ['shell', 'slurm'] and not is_worker:
         from mpi4py import MPI
         if MPI.COMM_WORLD.size != 1:
             err_msg = 'Do not launch `pytest_parallel` on more that one process when `--scheduler=shell` or `--scheduler=slurm`.\n' \
                       '`pytest_parallel` will spawn MPI processes itself.\n' \
                      f'You may want to use --n-workers={MPI.COMM_WORLD.size}.'
-            raise PytestParallelError(err_msg)
+            raise PytestParallelUsageError(err_msg)
 
 
 
     if scheduler == 'slurm' and not is_worker:
         if slurm_options is None and slurm_file is None:
-            raise PytestParallelError('You need to specify either `--slurm-options` or `--slurm-file` when `--scheduler=slurm`')
+            raise PytestParallelUsageError('You need to specify either `--slurm-options` or `--slurm-file` when `--scheduler=slurm`')
         if slurm_options:
             if slurm_file:
-                raise PytestParallelError('You need to specify either `--slurm-options` or `--slurm-file`, but not both')
+                raise PytestParallelUsageError('You need to specify either `--slurm-options` or `--slurm-file`, but not both')
         if slurm_file:
             if slurm_options:
-                raise PytestParallelError('You need to specify either `--slurm-options` or `--slurm-file`, but not both')
+                raise PytestParallelUsageError('You need to specify either `--slurm-options` or `--slurm-file`, but not both')
             if slurm_init_cmds:
-                raise PytestParallelError('You cannot specify `--slurm-init-cmds` together with `--slurm-file`')
+                raise PytestParallelUsageError('You cannot specify `--slurm-init-cmds` together with `--slurm-file`')
 
         if '-n=' in slurm_options or '--ntasks=' in slurm_options:
-            raise PytestParallelError('Do not specify `-n/--ntasks` in `--slurm-options` (it is deduced from the `--n-worker` value).')
+            raise PytestParallelUsageError('Do not specify `-n/--ntasks` in `--slurm-options` (it is deduced from the `--n-worker` value).')
 
         from .slurm_scheduler import SlurmScheduler
 

pytest_parallel/shell_static_scheduler.py

@@ -3,6 +3,7 @@
 import subprocess
 import socket
 import pickle
+from pathlib import Path
 
 import pytest
 from mpi4py import MPI
@@ -12,6 +13,7 @@
 from .utils.items import add_n_procs, run_item_test, mark_original_index, mark_skip
 from .utils.file import remove_exotic_chars, create_folders
 from .static_scheduler_utils import group_items_by_parallel_steps
+from .exception import PytestParallelEnvError
 
 def mpi_command(current_proc, n_proc):
     mpi_vendor = MPI.get_vendor()[0]
@@ -39,6 +41,7 @@ def submit_items(items_to_run, SCHEDULER_IP_ADDRESS, port, session_folder, main_
     for item in items:
         test_idx = item.original_index
         test_out_file = f'.pytest_parallel/{session_folder}/{remove_exotic_chars(item.nodeid)}'
+        test_out_file = str(Path(test_out_file).absolute()) # easier to find the file if absolute
         cmd = '('
         cmd += mpi_command(current_proc, item.n_proc)
         cmd += f' python3 -u -m pytest -s --_worker {socket_flags} {main_invoke_params} --_test_idx={test_idx} {item.config.rootpath}/{item.nodeid}'
@@ -106,6 +109,14 @@ def __init__(self, main_invoke_params, ntasks, detach):
 
         self.socket             = socket.socket(socket.AF_INET, socket.SOCK_STREAM) # TODO close at the end
 
+        # Check that MPI can be called in a subprocess (not the case with OpenMPI 4.0.5, see #17)
+        p = subprocess.run('mpirun -np 1 echo mpi_can_be_called_from_subprocess', shell=True)
+        if p.returncode != 0:
+            raise PytestParallelEnvError(
+                "Your MPI implementation does not handle MPI being called from a sub-process\n"
+                "Either update your MPI version or use another scheduler. See https://github.com/onera/pytest_parallel/issues/17"
+            )
+
     @pytest.hookimpl(tryfirst=True)
     def pytest_pyfunc_call(self, pyfuncitem):
         # This is where the test is normally run.

pytest_parallel/slurm_scheduler.py

@@ -1,6 +1,7 @@
 import subprocess
 import socket
 import pickle
+from pathlib import Path
 
 import pytest
 
@@ -44,6 +45,7 @@ def submit_items(items_to_run, socket, session_folder, main_invoke_params, ntask
     for item in items:
         test_idx = item.original_index
         test_out_file = f'.pytest_parallel/{session_folder}/{remove_exotic_chars(item.nodeid)}'
+        test_out_file = str(Path(test_out_file).absolute()) # easier to find the file if absolute
         cmd = '('
         cmd += f'srun {srun_options}'
         cmd +=  ' --exclusive'