<< Chapter < Page Chapter >> Page >

Il codice che segue effettua la lettura periodica di una linea di testo da un sito generatore di testo. Lo siestenda aggiungendo un thread che visualizza queste frasi sulla finestra grafica con animazione tipografica. class sentenceReader extends Thread{ int timediff; // quanto temporalesentenceReader(int td) {timediff = td; }void run() {while(true) { try {BufferedReader stdiin = createReader("http://www.essl.at/cgi-bin/swrap/cgis/lexikon-orakel.pl"); for (int i=0; i<13; i++) stdiin.readLine(); println(stdiin.readLine());sleep(timediff); }catch(Exception e){}} }} void setup() {sentenceReader st = new sentenceReader(2000); st.start();} void draw() {}


Si supponga di dover estendere la lettura di comandi da tastiera con due thread che prendono comandi da stdin . I comandi possono essere consumati dall'uno o dall'altro dei thread, ma uno stessocomando non può essere consumato da entrambi. In questo caso si possono presentare problemi di race condition , cioè configurazioni di codice concorrente che danno luogo a risultati dipendenti dalla sequenza di scheduling attribuita ai vari thread. In particolare, la sezione critica results=stdin.toString(); stdin.setLength(0);linea = false; può dare luogo a comportamenti inconsistenti se interrotta dallo scheduler per passare il controllo dall'uno all'altro thread. Questi problemi si possonorisolvere imponendo la non interrompibilità delle sezioni critiche di codice, per mezzo della parola chiave synchronized . Nella fattispecie, si può introdurre una classe con metodi sincronizzati: class IO extends Thread { String results;synchronized String acquire() { results=stdin.toString();linea = false; stdin.setLength(0);return(results); }} I metodi invocati su un oggetto di questa classe non sono interrompibili da metodi invocati sullo stesso oggetto. In ambito ditransazioni bancarie, per esempio, un metodo prelievo() dovrà essere sincronizzato per evitare inconsistenze in presenza di prelievi multipli, come possono essere effettuati da co-titolari dellostesso conto. La sincronizzazione di thread è un argomento complesso, per l'approfondimento del quale esistono libri specializzati .

Si estenda la lettura di comandi da tastiera con due thread che prendono comandi da stdin .

Nel codice seguente si noti l'uso della getName() per stampare il nome del thread interessato. StringBuffer stdin; boolean linea;color colore; IO io = new IO();void keyReleased() { char c = key;if (c!='\n') { stdin.append(c);} else linea=true;} class IO extends Thread {String results; synchronized String acquire() {results=stdin.toString(); linea = false;stdin.setLength(0); return(results);} }class ColorInput extends Thread { String results;char c;void ColorInput (IO inout) { io = inout;} void run() {while(true) { if (linea) {results=io.acquire(); println(this.getName() + results);if (results.equals("rosso")) { colore = color(255, 0, 0);} if (results.equals("verde")) {colore = color(0, 255, 0); }if (results.equals("blu")) { colore = color(0, 0, 255);} }try { sleep(2); // to relief the cpu from active waiting} catch (Exception e) {println("Exception in sleep");} }} }class TimerThread extends Thread{ int timediff; // quanto temporaleTimerThread(int td) {timediff = td; }void run() {while(true) { try {fill(colore); ellipse(int(random(100)), int(random(100)),int(random(20)), int(random(20))); sleep(timediff);} catch (Exception e) {println("Exception in sleep");} }} }void setup() { stdin = new StringBuffer();TimerThread tt1 = new TimerThread(100); ColorInput ci = new ColorInput();ColorInput ci2 = new ColorInput(); ci.start(); ci2.start();tt1.start(); }void draw() { }


Il capitolo 9 del libro Visualizing Data -- Ben Fry; O'Really 2007 fornisce esempi di acquisizione asincrona di dati da file e da sitiremoti, con l'utilizzazione di thread e di sincronizzazione.

Questions & Answers

how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
can nanotechnology change the direction of the face of the world
Prasenjit Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Berger describes sociologists as concerned with
Mueller Reply
Got questions? Join the online conversation and get instant answers!
QuizOver.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Programmazione di artefatti interattivi. OpenStax CNX. Dec 09, 2010 Download for free at http://cnx.org/content/col10417/1.9
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Programmazione di artefatti interattivi' conversation and receive update notifications?