Fixed the parallel print module

Fix issue for parallel print error
To test if the code works correctly in parallel

Author: mesonepigreco

Modules/Parallel.py

@@ -4,8 +4,10 @@
 modules.
 """
 
-import numpy as np 
+import numpy as np
 import time
+import os
+import sys
 
 # Supports both pypar and mpi4py
 __PYPAR__ = False 
@@ -46,14 +48,53 @@ def am_i_the_master():
     else:
         return True 
 
-def pprint(*argv):
+def _force_stdout_blocking():
+    """
+    Make sure the standard output is in blocking mode.
+
+    MPI launchers (mpirun, srun, ...) frequently attach the standard output
+    of the processes to a pipe that is opened in *non-blocking* mode. When a
+    large message fills the pipe buffer, a write on a non-blocking descriptor
+    raises ``BlockingIOError`` ([Errno 11]) instead of waiting for the buffer
+    to drain. This used to crash a parallel minimization while printing the
+    table of imaginary frequencies (see issue #196).
+
+    Restoring the blocking mode makes the write wait for the reader to consume
+    the buffer, which is the expected behaviour for log output.
+    """
+    if not hasattr(os, "set_blocking"):
+        return
+    try:
+        fd = sys.stdout.fileno()
+    except (AttributeError, OSError, ValueError):
+        # stdout has been replaced by an object without a real descriptor
+        return
+    try:
+        os.set_blocking(fd, True)
+    except (OSError, ValueError):
+        pass
+
+
+def pprint(*argv, **kwargs):
     """
     PARALLEL PRINTING
     =================
 
-    This will print on stdout only once in parallel execution of the code
+    This will print on stdout only once in parallel execution of the code.
+
+    It is robust against a standard output opened in non-blocking mode, which
+    is a frequent source of ``BlockingIOError`` when running under MPI (see
+    issue #196): a log line must never abort a running calculation.
     """
     #print("pypar:", __PYPAR__)
     #print("mpi4py:", __MPI4PY__)
-    if am_i_the_master():
-        print(*argv)
+    if not am_i_the_master():
+        return
+
+    _force_stdout_blocking()
+    try:
+        print(*argv, **kwargs)
+    except BlockingIOError:
+        # The blocking mode could not be enforced (e.g. os.set_blocking is
+        # not available or failed). Never let a print crash the calculation.
+        pass