remove semaphore from cga_stream

c_os/user/demo/PreemptiveThreadDemo.cc

@@ -1,21 +1,19 @@
 #include "user/demo/PreemptiveThreadDemo.h"
 
+Semaphore PreemptiveLoopThread::sem(1);
+
 void PreemptiveLoopThread::run() {
     int cnt = 0;
 
     while (true) {
         // Basic synchronization by semaphore
-        // NOTE: I placed the semaphore inside the CGA_Stream so multiple demos can synchronize, not
-        //       only this one. This is optional so disruptions can still occur because of preemption
-        //       (I only use this for the user output (demos), anywhere else could become problematic
-        //        quickly...)
-        kout.lock();
+        sem.p();
 
         // Saving + restoring kout position doesn't help much as preemption still occurs
         kout.setpos(55, this->id);
         kout << fillw(3) << this->id << fillw(0) << ": " << dec << cnt++ << endl;
 
-        kout.unlock();
+        sem.v();
     }
 }