Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Erlang processes correspond (approximately) to <a href="http://en.wikipedia.org/wiki/Green_threads" rel="noreferrer">green threads</a> in other languages; there's no OS-enforced separation between the processes. (There may well be language-enforced separation, but that's a lesser protection despite Erlang doing a better job than most.) Because they're so much lighter-weight, they can be used far more extensively.</p> <p>OS threads on the other hand are able to be simply scheduled on different CPU cores, and are (mostly) able to support independent CPU-bound processing. OS processes are like OS threads, but with much stronger OS-enforced separation. The price of these capabilities is that OS threads and (even more so) processes are more expensive.</p> <hr> <p>Another way to understand the difference is this. Supposing you were going to write an implementation of Erlang on top of the JVM (not a particularly crazy suggestion) then you'd make each Erlang process be an object with some state. You'd then have a pool of Thread instances (typically sized according to the number of cores in your host system; that's a tunable parameter in real Erlang runtimes BTW) which run the Erlang processes. In turn, that will distribute the work that is to be done across the real system resources available. It's a pretty neat way of doing things, but relies <em>utterly</em> on the fact that each individual Erlang process doesn't do very much. That's OK of course; Erlang is structured to not require those individual processes to be heavyweight since it is the overall ensemble of them which execute the program.</p> <p>In many ways, the real problem is one of terminology. The things that Erlang calls processes (and which correspond strongly to the same concept in CSP, CCS, and particularly the π-calculus) are simply not the same as the things that languages with a C heritage (including C++, Java, C#, and many others) call a process or a thread. There are <em>some</em> similarities (all involve some notion of concurrent execution) but there's definitely no equivalence. So be careful when someone says “process” to you; they might understand it to mean something utterly different…</p>
    singulars
    1. This table or related slice is empty.
    1. POTechnically, why are processes in Erlang more efficient than OS threads?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USDonal Fellows
    1. USDonal Fellows
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTDownMod
    1. COErlang doesn't get anywhere close to Pi Calculus. Pi calculus assumes synchronous events over channels that can be bound to variables. This kind of concept doesn't fit the Erlang model at all. Try Join Calculus, Erlang's closer to that although it still needs to be able to natively join on some messages and whatnot. There was a thesis paper (and project) named JErlang dedicated which implemented it.
      singulars
      1. PO
      1. USI GIVE TERRIBLE ADVICE
    2. COIt all depends on what exactly you view the pi-calculus to be (and you can model asynchronous channels with synchronous channels plus buffer processes).
      singulars
      1. PO
      1. USDonal Fellows
    3. COYou are just saying that Erlang processes are lightweight but you are not explaining why they have a smaller footprint (are lightweight) and why they have better performance than OS threads.
      singulars
      1. PO
      1. USJonas
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload