Cum să rulați mai multe fire simultan în Java? Abordarea ExecutorService

Publicat: 2021-10-09
Cum să rulați mai multe fire simultan în Java? Abordarea ExecutorService

Să aruncăm o privire din nou la acest exemplu: Cum să obțineți starea Ping a oricărui punct final HTTP în Java?

Ați observat execuția firului pentru acel exemplu? Este secvenţial. What if you have 500 endpoints? Pun pariu că trebuie să așteptați cel puțin 5 minute pentru a obține rezultat. Ceea ce sunt sigur că nu este cea mai bună soluție.

Acum ce? Întrebarea corectă ar fi:

  • Cum să rulezi mai multe fire simultan?
  • Cum se implementează mai multe fire în Java?
  • Cum rulez fire diferite în Java?
  • Java – Unde este Tutorialul de programare multithreading?
  • Thread: Cum să utilizați mai multe fire pentru a accelera procesarea?

ExecutorService Approach este răspunsul tău.

Un Executor care oferă metode de gestionare a rezilierii și metode care pot produce un viitor pentru urmărirea progresului uneia sau mai multor sarcini asincrone.

Un ExecutorService poate fi oprit, ceea ce îl va determina să respingă noi sarcini. Sunt furnizate două metode diferite pentru închiderea unui ExecutorService. Metoda shutdown() va permite executarea sarcinilor trimise anterior înainte de terminare, în timp ce metoda shutdownNow() împiedică pornirea sarcinilor în așteptare și încercările de a opri executarea sarcinilor curente.

La reziliere, un executor nu are sarcini în execuție activă, nicio sarcină în așteptare de executare și nicio sarcină nouă nu poate fi depusă. Un ExecutorService neutilizat ar trebui să fie închis pentru a permite recuperarea resurselor sale.

Metoda de trimitere extinde metoda de bază Executor.execute ( java.lang.Runnable ) prin crearea și returnarea unui viitor care poate fi folosit pentru a anula execuția și/sau a aștepta finalizarea. Metodele invokeAny și invokeAll efectuează cele mai frecvente forme utile de execuție în bloc, executând o colecție de sarcini și apoi așteptând ca cel puțin una sau toate să fie finalizate. (Class ExecutorCompletionService poate fi folosit pentru a scrie variante personalizate ale acestor metode.)

Clasa Executors oferă metode din fabrică pentru serviciile de executor furnizate în acest pachet.

  • java – ExecutorService, cum să așteptați ca toate sarcinile să se termine?
  • Un ghid pentru Java ExecutorService
  • Java Thread Pool – Explicație ExecutorService

Mai jos este un exemplu Java simplu care explică usage of ExecutorService .

Java
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package crunchify . com . tutorials ;
 
import java . net . HttpURLConnection ;
import java . net . URL ;
import java . util . concurrent . ExecutorService ;
import java . util . concurrent . Executors ;
 
/**
* @author Crunchify.com
* How to Run Multiple Threads Concurrently in Java? ExecutorService Approach.
*/
 
public class CrunchifyGetPingStatusWithExecutorService {
private static final int crunchifyThreads = 30 ;
public static void main ( String [ ] args ) throws Exception {
// Executors: Factory and utility methods for Executor, ExecutorService, ScheduledExecutorService, ThreadFactory, and Callable classes defined in this package.
// ExecutorService: An Executor that provides methods to manage termination and methods that can produce a Future for tracking progress of one or more asynchronous tasks.
// An ExecutorService can be shut down, which will cause it to reject new tasks.
// Two different methods are provided for shutting down an ExecutorService.
// The shutdown method will allow previously submitted tasks to execute before terminating, while the shutdownNow method prevents waiting tasks from starting and attempts to stop currently executing tasks.
// Upon termination, an executor has no tasks actively executing, no tasks awaiting execution, and no new tasks can be submitted.
// An unused ExecutorService should be shut down to allow reclamation of its resources.
ExecutorService executor = Executors . newFixedThreadPool ( crunchifyThreads ) ;
// newFixedThreadPool(): Creates a thread pool that reuses a fixed number of threads operating off a shared unbounded queue.
// At any point, at most nThreads threads will be active processing tasks. If additional tasks are submitted when all threads are active, they will wait in the queue until a thread is available.
// If any thread terminates due to a failure during execution prior to shutdown, a new one will take its place if needed to execute subsequent tasks
String [ ] crunchifyList = {
"https://crunchify.com" ,
"https://yahoo.com" ,
"https://www.ebay.com" ,
"https://google.com" ,
"https://www.example.co" ,
"https://paypal.com" ,
"http://bing.com/" ,
"https://techcrunch.com/" ,
"http://mashable.com/" ,
"https://pro.crunchify.com/" ,
"https://wordpress.com/" ,
"https://wordpress.org/" ,
"https://example.com/" ,
"https://sjsu.edu/" ,
"https://ask.crunchify.com/" ,
"https://test.com.au/" ,
"https://www.wikipedia.org/" ,
"https://en.wikipedia.org"
} ;
for ( int i = 0 ; i < crunchifyList . length ; i ++ ) {
String url = crunchifyList [ i ] ;
Runnable worker = new MyRunnable ( url ) ;
// execute(): Executes the given command at some time in the future. The command may execute in a new thread, in a pooled thread,
// or in the calling thread, at the discretion of the Executor implementation.
executor . execute ( worker ) ;
}
// shutdown(): Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.
// Invocation has no additional effect if already shut down.
// This method does not wait for previously submitted tasks to complete execution. Use awaitTermination to do that.
executor . shutdown ( ) ;
// Wait until all threads are finish
// Returns true if all tasks have completed following shut down.
// Note that isTerminated is never true unless either shutdown or shutdownNow was called first.
while ( ! executor . isTerminated ( ) ) {
     // empty body
}
System . out . println ( "\nFinished all threads" ) ;
}
// Runnable: The Runnable interface should be implemented by any class whose instances are intended to be executed by a thread.
// The class must define a method of no arguments called run.
public static class MyRunnable implements Runnable {
private final String url ;
MyRunnable ( String url ) {
this . url = url ;
}
@Override
public void run ( ) {
String result = "" ;
int code = 200 ;
try {
URL siteURL = new URL ( url ) ;
// HttpURLConnection: A URLConnection with support for HTTP-specific features. See the spec for details.
// openConnection(): Returns a URLConnection instance that represents a connection to the remote object referred to by the URL.
HttpURLConnection connection = ( HttpURLConnection ) siteURL . openConnection ( ) ;
// setRequestMethod: Set the method for the URL request, one of:
//GET
//POST
//HEAD
//OPTIONS
//PUT
//DELETE
//TRACE
connection . setRequestMethod ( "GET" ) ;
// setConnectTimeout(): Sets a specified timeout value, in milliseconds, to be used when opening a communications link to the resource referenced by this URLConnection.
// If the timeout expires before the connection can be established, a java.net
connection . setConnectTimeout ( 3000 ) ;
// connect(): Opens a communications link to the resource referenced by this URL, if such a connection has not already been established.
connection . connect ( ) ;
// getResponseCode(): Gets the status code from an HTTP response message. For example, in the case of the following status lines:
//       HTTP/1.0 200 OK
//       HTTP/1.0 401 Unauthorized
code = connection . getResponseCode ( ) ;
if ( code == 200 ) {
result = "-> Green <-\t\t" + "Code: " + code ;
;
} else {
result = "-> Yellow <-\t\t" + "Code: " + code ;
}
} catch ( Exception e ) {
result = "-> Red <-\t\t" + "Wrong domain - Exception: " + e . getMessage ( ) ;
}
System . out . println ( url + "\t\t\t\tStatus:" + result ) ;
}
}
}

Ieșire:

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/ Users / app / . m2 / repository / org / slf4j / slf4j - api / 1.7.31 / slf4j - api - 1.7.31.jar : / Users / app / . m2 / repository / org / slf4j / jul - to - slf4j / 1.7.31 / jul - to - slf4j - 1.7.31.jar : / Users / app / . m2 / repository / org / slf4j / jcl - over - slf4j / 1.7.31 / jcl - over - slf4j - 1.7.31.jar : / Users / app / . m2 / repository / org / slf4j / log4j - over - slf4j / 1.7.31 / log4j - over - slf4j - 1.7.31.jar crunchify . com . tutorials . CrunchifyGetPingStatusWithExecutorService
 
http : //mashable.com/ Status:-> Yellow <- Code: 301
http : //bing.com/ Status:-> Green <- Code: 200
https : //www.example.co Status:-> Red <- Wrong domain - Exception: www.example.co
https : //example.com/ Status:-> Green <- Code: 200
https : //wordpress.com/ Status:-> Green <- Code: 200
https : //www.wikipedia.org/ Status:-> Green <- Code: 200
https : //test.com.au/ Status:-> Yellow <- Code: 301
https : //wordpress.org/ Status:-> Green <- Code: 200
https : //techcrunch.com/ Status:-> Green <- Code: 200
https : //www.ebay.com Status:-> Green <- Code: 200
https : //ask.crunchify.com/ Status:-> Green <- Code: 200
https : //en.wikipedia.org Status:-> Green <- Code: 200
https : //crunchify.com Status:-> Green <- Code: 200
https : //sjsu.edu/ Status:-> Green <- Code: 200
https : //pro.crunchify.com/ Status:-> Green <- Code: 200
https : //google.com Status:-> Green <- Code: 200
https : //paypal.com Status:-> Green <- Code: 200
https : //yahoo.com Status:-> Green <- Code: 200
 
Finished all threads
 
Process finished with exit code 0

Acum verificați rezultatul.

Ar trebui să fie în doar câteva secunde. Sper că veți găsi acest lucru de ajutor. Încercați să rulați acest lucru de mai multe ori și este posibil să vedeți un rezultat diferit, deoarece toate firele de execuție se execută în paralel, iar cine obține vreodată un rezultat rapid, va vedea rezultatul postat în consola Eclipse.

Anunță-mă pentru orice întrebare.