Allow user to force thread number

This allows the user to do (potentially) stupid things, but warns him.
The default is TBBs default, so probably the right thing.
To enforce thread numbers in extractor it must be passed to the child
threads.

Extractor/PBFParser.cpp

@@ -40,6 +40,7 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include "../typedefs.h"
 
 #include <tbb/parallel_for.h>
+#include <tbb/task_scheduler_init.h>
 
 #include <osrm/Coordinate.h>
 
@@ -51,9 +52,19 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 PBFParser::PBFParser(const char *fileName,
                      ExtractorCallbacks *extractor_callbacks,
-                     ScriptingEnvironment &scripting_environment)
+                     ScriptingEnvironment &scripting_environment,
+                     unsigned num_threads)
     : BaseParser(extractor_callbacks, scripting_environment)
 {
+    if (0 == num_threads)
+    {
+        num_parser_threads = tbb::task_scheduler_init::default_num_threads();
+    }
+    else
+    {
+        num_parser_threads = num_threads;
+    }
+
     GOOGLE_PROTOBUF_VERIFY_VERSION;
     // TODO: What is the bottleneck here? Filling the queue or reading the stuff from disk?
     // NOTE: With Lua scripting, it is parsing the stuff. I/O is virtually for free.
@@ -160,6 +171,8 @@ inline void PBFParser::ReadData()
 
 inline void PBFParser::ParseData()
 {
+    tbb::task_scheduler_init init(num_parser_threads);
+
     while (true)
     {
         ParserThreadData *thread_data;

Extractor/PBFParser.h

@@ -63,7 +63,10 @@ class PBFParser : public BaseParser
     };
 
   public:
-    PBFParser(const char *file_name, ExtractorCallbacks *extractor_callbacks, ScriptingEnvironment &scripting_environment);
+    PBFParser(const char *file_name,
+              ExtractorCallbacks *extractor_callbacks,
+              ScriptingEnvironment &scripting_environment,
+              unsigned num_parser_threads=0);
     virtual ~PBFParser();
 
     inline bool ReadHeader();
@@ -94,6 +97,7 @@ class PBFParser : public BaseParser
 
     std::fstream input; // the input stream to parse
     std::shared_ptr<ConcurrentQueue<ParserThreadData *>> thread_data_queue;
+    unsigned num_parser_threads;
 };
 
 #endif /* PBFPARSER_H_ */