¿Cómo ejecutar múltiples subprocesos simultáneamente en Java? Enfoque ExecutorService

Publicado: 2021-10-09
¿Cómo ejecutar múltiples subprocesos simultáneamente en Java? Enfoque ExecutorService

Echemos un vistazo a este ejemplo nuevamente: ¿Cómo obtener el estado de ping de cualquier punto final HTTP en Java?

¿Has notado la ejecución del hilo para ese ejemplo? es secuencial What if you have 500 endpoints? Apuesto a que tienes que esperar al menos 5 minutos para obtener el resultado. Que estoy seguro que no es la mejor solución.

¿Ahora que? La pregunta correcta sería:

  • ¿Cómo ejecutar múltiples subprocesos al mismo tiempo?
  • ¿Cómo implementar múltiples hilos en Java?
  • ¿Cómo ejecuto diferentes subprocesos en Java?
  • Java: ¿dónde está el tutorial de programación de subprocesos múltiples?
  • Subproceso: ¿Cómo usar múltiples subprocesos para acelerar el procesamiento?

ExecutorService Approach es su respuesta.

Un Ejecutor que proporciona métodos para administrar la terminación y métodos que pueden producir un Futuro para rastrear el progreso de una o más tareas asincrónicas.

Se puede cerrar un ExecutorService, lo que hará que rechace nuevas tareas. Se proporcionan dos métodos diferentes para cerrar un ExecutorService. El método shutdown() permitirá que las tareas enviadas anteriormente se ejecuten antes de finalizar, mientras que el método shutdownNow() evita que se inicien las tareas en espera e intenta detener las tareas que se están ejecutando actualmente.

Al finalizar, un ejecutor no tiene tareas en ejecución activa, no hay tareas en espera de ejecución y no se pueden enviar tareas nuevas. Un ExecutorService no utilizado debe cerrarse para permitir la recuperación de sus recursos.

El envío del método amplía el método base Executor.execute ( java.lang.Runnable ) al crear y devolver un futuro que se puede usar para cancelar la ejecución y/o esperar a que se complete. Los métodos invokeAny e invokeAll realizan las formas más comúnmente útiles de ejecución masiva, ejecutando una colección de tareas y luego esperando que se complete al menos una o todas. (Class ExecutorCompletionService se puede usar para escribir variantes personalizadas de estos métodos).

La clase Executors proporciona métodos de fábrica para los servicios de ejecución proporcionados en este paquete.

  • java – ExecutorService, ¿cómo esperar a que terminen todas las tareas?
  • Una guía para Java ExecutorService
  • Grupo de subprocesos de Java: explicación de ExecutorService

A continuación se muestra un ejemplo de Java simple que explica el 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 ) ;
}
}
}

Producción:

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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

Ahora revisa el resultado.

Debería ser en unos segundos. Espero que encuentres esto útil. Intente ejecutar esto más de una vez y es posible que vea un resultado diferente, ya que todos los subprocesos se ejecutan en paralelo y quien obtenga un resultado rápido, verá el resultado publicado en la consola de Eclipse.

Avisame para cualquier consulta.