.tutorial

git-svn-id: svn://ultimatepp.org/upp/trunk@10557 f0d560ea-af0d-0410-9eb7-867de7ffcac7

tutorial/CoreTutorial/ConditionVariable.cpp

@@ -0,0 +1,50 @@
+#include "Tutorial.h"
+
+void ConditionVariableTutorial()
+{
+	/// .`ConditionVariable`
+	
+	/// `ConditionVariable` in general is a synchronization primitive used to block/awaken the
+	/// thread. `ConditionVariable` is associated with `Mutex` used to protect some data; in
+	/// the thread that is to be blocked, `Mutex` has to locked; call to `Wait` atomically
+	/// unlocks the `Mutex` and puts the thread to waiting. Another thread then can resume the
+	/// thread by calling `Signal`, which also causes `Mutex` to lock again. Multiple threads
+	/// can be waiting on single `ConditionVariable`; `Signal` resumes single waiting thread,
+	/// `Brodcast` resumes all waitng threads.
+	
+	bool  stop = false;
+	BiVector<int> data;
+	Mutex m;
+	ConditionVariable cv;
+	
+	Thread t;
+	t.Run([&stop, &data, &m, &cv] {
+		Mutex::Lock __(m);
+		for(;;) {
+			while(data.GetCount()) {
+				int q = data.PopTail();
+				LOG("Data received: " << q);
+			}
+			if(stop)
+				break;
+			cv.Wait(m);
+		}
+	});
+	
+	for(int i = 0; i < 10; i++) {
+		{
+			Mutex::Lock __(m);
+			data.AddHead(i);
+		}
+		cv.Signal();
+		Sleep(1);
+	}
+	stop = true;
+	cv.Signal();
+	t.Wait();
+	
+	/// Important note: rarely thread can be resumed from `Wait` even if no other called
+	/// `Signal`. This is not a bud, but ^https://en.wikipedia.org/wiki/Spurious_wakeup:design
+	/// decision for performance reason^. In practice it only means that situation has to be
+	/// (re)checked after resume.
+}