Singleton: Difference between revisions

=={{header|D}}==

<d>module singleton ;

import std.stdio ;

import std.thread ;

import std.random ;

import std.c.time ;

class Dealer {

static Dealer me ;

static Dealer Instance() {

synchronized { // this part of code can only be executed by one thread a time

if(me is null) {

// some delay so that other threads has chance to call this synchronized code

for(int i = 0 ; i < 6 ; i++) {

writefln("...calling Dealer... ") ;

msleep(rand() & 2048) ;

}

me = new Dealer ;

}

}

return me ;

}

static string[] str = ["(1)Enjoy", "(2)Rosetta", "(3)Code"] ;

int state ;

private this() {

writefln(">>Dealer is called to come in!") ;

state = str.length - 1 ;

}

Dealer nextState() {

synchronized {

state = (state + 1) % str.length ;

}

return this ;

}

string toString() { return str[state] ; }

}

class Coder : Thread {

string name_ ;

Coder hasName(string name) { name_ = name ; return this ; }

override int run() {

msleep(rand() & 512) ;

writefln(">>%s come in.", name_) ;

Dealer single = Dealer.Instance ;

msleep(rand() & 512) ;

for(int i = 0 ; i < 3 ; i++) {

writefln("%9s got %-s", name_, single.nextState) ;

msleep(rand() & 1024) ;

}

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 ;

}</d>

Sample Output:

<pre>>>Peter come in.

...calling Dealer...

...calling Dealer...

...calling Dealer...

...calling Dealer...

...calling Dealer...

>>Paul come in.

>>Mary come in.

...calling Dealer...

>>Dealer is called to come in!

Mary got (1)Enjoy

Paul got (2)Rosetta

Mary got (3)Code

Peter got (1)Enjoy

Paul got (2)Rosetta

Mary got (3)Code

Paul got (1)Enjoy

Peter got (2)Rosetta

Peter got (3)Code</pre>