Use thread local stack for trace.

	*  mln/core/trace.hpp: thread local stack.

mln/core/trace.hpp

@@ -7,7 +7,11 @@
 # include <iostream>
 # include <stack>
 # include <string>
-# include <mutex>
+//# include <mutex>
+# include <thread>
+# include <tbb/compat/thread>
+# include <tbb/combinable.h>
+# include <tbb/tick_count.h>
 
 # define mln_entering(NAME) \
   mln::trace::entering(NAME);
@@ -24,26 +28,29 @@ namespace mln
       explicit trace_t(const std::string& fun)
 	: fname (fun)
       {
-	clock = std::clock();
+	clock = tbb::tick_count::now();
       }
 
-      std::string  fname;
-      std::clock_t clock;
+      std::string       fname;
+      tbb::tick_count   clock;
     };
 
-
-    static std::stack<trace_t> callstack;
+    static tbb::combinable< std::stack<trace_t> > callstacks;
+    //static std::stack<trace_t> callstack;
     static bool verbose = (std::getenv("TRACE") != NULL);
-    static std::mutex stack_mutex;
+    //static std::mutex stack_mutex;
 
     static inline
     void entering(const std::string& fname)
     {
       if (verbose) {
-        std::lock_guard<std::mutex> lock(stack_mutex);
+        //std::lock_guard<std::mutex> lock(stack_mutex);
+        std::stack<trace_t>& callstack = callstacks.local();
         callstack.emplace(fname);
 
-	std::clog << std::string(callstack.size(), ' ') << fname << std::endl;
+	std::clog << std::string(callstack.size(), ' ')
+                  << "#" << std::this_thread::get_id() << " - "
+                  << fname << std::endl;
       }
     };
 
@@ -52,11 +59,13 @@ namespace mln
     void exiting()
     {
       if (verbose) {
-        std::lock_guard<std::mutex> lock(stack_mutex);
-
+        //std::lock_guard<std::mutex> lock(stack_mutex);
+        std::stack<trace_t>& callstack = callstacks.local();
 	trace_t tr = callstack.top();
-	std::clog << std::string(callstack.size(), ' ') << tr.fname
-		  << " in " << ((float)(std::clock() - tr.clock) / CLOCKS_PER_SEC) << std::endl;
+	std::clog << std::string(callstack.size(), ' ')
+                  << "#" << std::this_thread::get_id() << " - "
+                  << tr.fname
+		  << " in " << (tbb::tick_count::now() - tr.clock).seconds() << std::endl;
 
         callstack.pop();
       }
@@ -66,7 +75,9 @@ namespace mln
     void warn(const std::string& msg)
     {
       if (verbose)
-        std::clog << std::string(callstack.size(), ' ') << msg << std::endl;
+        std::clog << std::string(callstacks.local().size(), ' ')
+                  << "#" << std::this_thread::get_id() << " - "
+                  << msg << std::endl;
     }
 
   }