Data commit

Task/Singleton/D/singleton.d

@@ -0,0 +1,61 @@
+module singleton ;
+import std.stdio ;
+import std.thread ;
+import std.random ;
+import std.c.time ;
+
+class Dealer {
+  private static Dealer me ;
+  static Dealer Instance() {
+    writefln("   Calling Dealer... ") ;
+    if(me is null) // Double Checked Lock
+      synchronized  // this part of code can only be executed by one thread a time
+        if(me is null)
+          me = new Dealer ;
+    return me ;
+  }
+  private static string[] str = ["(1)Enjoy", "(2)Rosetta", "(3)Code"] ;
+  private int state ;
+  private this() {
+    for(int i = 0 ; i < 3 ; i++) {
+      writefln("...calling Dealer... ") ;
+      msleep(rand() & 2047) ;
+    }
+    writefln(">>Dealer is called to come in!") ;
+    state = str.length - 1 ;
+  }
+  Dealer nextState() {
+    synchronized(this) // accessed to Object _this_ is locked ... is it necessary ???
+      state = (state + 1) % str.length ;
+    return this ;
+  }
+  string toString() { return str[state] ; }
+}
+
+class Coder : Thread {
+  private string name_ ;
+  Coder hasName(string name) {  name_ = name ; return this ; }
+  override int run() {
+    msleep(rand() & 1023) ;
+    writefln(">>%s come in.", name_) ;
+    Dealer single = Dealer.Instance ;
+    msleep(rand() & 1023) ;
+    for(int i = 0 ; i < 3 ; i++) {
+      writefln("%9s got %-s", name_, single.nextState) ;
+      msleep(rand() & 1023) ;
+    }
+    return 0 ;
+  }
+}
+
+void main() {
+  Coder x = new Coder ;
+  Coder y = new Coder ;
+  Coder z = new Coder ;
+
+  x.hasName("Peter").start() ;
+  y.hasName("Paul").start() ;
+  z.hasName("Mary").start() ;
+
+  x.wait ;  y.wait ;  z.wait ;
+}