Fix solver communication deadlocks

Calling wait() on process object that communicates through pipes causes
deadlocks when the pipes fill up. To fix this, communicate() method was used
to send data to the solver. Returned bytes objects were converted to BytesIO
objects to keep compatibility with existing processing.

pysollib/hint.py

@@ -28,6 +28,7 @@ import time
 import subprocess
 import re
 import sys
+from io import BytesIO
 
 # PySol imports
 from pysollib.settings import DEBUG, FCS_COMMAND
@@ -801,18 +802,14 @@ class Base_Solver_Hint:
         if os.name != 'nt':
             kw['close_fds'] = True
         p = subprocess.Popen(command, **kw)
-        pin, pout, perr = p.stdin, p.stdout, p.stderr
         bytes_board = board
         if sys.version_info > (3,):
             bytes_board = bytes(board, 'utf-8')
-        pin.write(bytes_board)
-        pin.close()
-        if os.name == 'posix':
-            p.wait()
+        pout, perr = p.communicate(bytes_board)
         if p.returncode in (127, 1):
             # Linux and Windows return codes for "command not found" error
             raise RuntimeError('Solver exited with {}'.format(p.returncode))
-        return pout, perr
+        return BytesIO(pout), BytesIO(perr)
 
 
 class FreeCellSolver_Hint(Base_Solver_Hint):
@@ -1091,8 +1088,6 @@ class FreeCellSolver_Hint(Base_Solver_Hint):
 
         pout.close()
         perr.close()
-        if os.name == 'posix':
-            os.wait()
 
 
 class BlackHoleSolver_Hint(Base_Solver_Hint):