Introducing a global variable to define the number of threads

* NEWS: Announce
* spot/Makefile.am: Add pthread to use threads
* spot/misc/common.cc,
  spot/misc/common.hh: Add variable + getter/setter
* spot/misc/Makefile.am: Add common.cc

NEWS

@@ -23,6 +23,9 @@ New in spot 2.10.6.dev  (not yet released)
 
   Library:
 
+  - A global variable, together with its setters and getters to define the
+    maximal number of threads is added to common.hh/common.cc
+
   - The new function suffix_operator_normal_form() implements
     transformation of formulas to Suffix Operator Normal Form,
     described in [cimatti.06.fmcad].

spot/Makefile.am

@@ -35,7 +35,7 @@ SUBDIRS = misc priv tl graph twa twacube twaalgos ta taalgos kripke \
 
 lib_LTLIBRARIES = libspot.la
 libspot_la_SOURCES =
-libspot_la_LDFLAGS = $(BUDDY_LDFLAGS) -no-undefined $(SYMBOLIC_LDFLAGS)
+libspot_la_LDFLAGS = $(BUDDY_LDFLAGS) -no-undefined -pthread $(SYMBOLIC_LDFLAGS)
 libspot_la_LIBADD =  \
   kripke/libkripke.la \
   misc/libmisc.la \

spot/misc/Makefile.am

@@ -63,6 +63,7 @@ libmisc_la_SOURCES = \
   bareword.cc \
   bitset.cc \
   bitvect.cc \
+  common.cc \
   escape.cc \
   formater.cc \
   intvcomp.cc \

spot/misc/common.cc

@@ -0,0 +1,33 @@
+// -*- coding: utf-8 -*-
+// Copyright (C) 2018 Laboratoire de Recherche et Développement
+// de l'Epita (LRDE).
+//
+// This file is part of Spot, a model checking library.
+//
+// Spot is free software; you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 3 of the License, or
+// (at your option) any later version.
+//
+// Spot is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+// or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+// License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#include "config.h"
+#include <spot/misc/common.hh>
+
+static unsigned N_MAX_THREADS = 1;
+
+void set_nthreads(unsigned nthreads)
+{
+  N_MAX_THREADS = nthreads;
+}
+
+unsigned get_nthreads()
+{
+  return N_MAX_THREADS;
+}

spot/misc/common.hh

@@ -169,3 +169,11 @@ namespace spot
 #  define SPOT_make_shared_enabled__(TYPE, ...)  \
    std::make_shared<TYPE>(__VA_ARGS__)
 #endif
+
+
+// Global variable to determine the maximal number of threads
+SPOT_API void
+set_nthreads(unsigned nthreads);
+
+SPOT_API unsigned
+get_nthreads();