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Sistem stateless si sisteme stateful

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Citeam un articol ce descria paraller programing. Si am ajuns la doi termeni care desi imi pareau cunoscuti nu imi erau foarte clar definiti.
Cei doi termeni sunt
  • stateless system;
  • stateful system;
Un sistem stateless este un sistem inchis, unde output-ul depinde doar de input si atata. Rezultatul obtinut nu este deloc influentat deloc de alte valori pe care sistemul le poate stoca intr-o forma sau alta.
In cazul acesta un exemplu ar putea sa fie:
Console.WriteLine(DateTime.UtcNow.ToString());
Oriunde pe glob ne-am afla si orice setare am aveam la masina( regional settings), valoarea returnata o sa fie aceiasi in orice locatie de pe glob. Acest sistem poate sa fie numit stateless din punct de vedere a regional settings.
Un sistem stateful este un sistem deschis, unde outpu-ul nu depinde doar de input. Pentru calcularea output-ului se i-au in considerare si alte valori. Poate fi vazut intr-o oarecare masura ca o masina de stari, care poate sa isi pastreze ultima stare.
Un bun exemplu este:
Console.WriteLine(DateTime.Now.ToString());
In functie de regional settings, o sa putem avea valori diferite afisate in zone diferite ale lumii, deoarece propietatea statica Now tine cont de regional settings.
Din punct de vedere a rularii in paralel, un sistem stateless este cel mai usor de implementat. Oricate thread-uri ar exista, acestea nu trebe sa partajeze/sincronizeze informatii. Fiecare isi poate face treaba cu input-ul pe care il are.
In cazul unui sistem stateful, programarea in paralel nu mai este atat de simpla. Pot sa apara cazuri cand mai multe resurse( stari ale masinii sau sistemului) sunt partajate intre mai multe theaduri, caz in care apare lucrurile se complica.
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