1 / 29

Multithreaded Programming in Java

Multithreaded Programming in Java. http://flic.kr/p/4Krva2. What is concurrent software?. A program with more than one thread of execution—more than one thing happens at once!. http://flic.kr/p/9ksxQa. Two Units of Execution. Process Has self-contained execution environment

moffit
Télécharger la présentation

Multithreaded Programming in Java

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Multithreaded Programming in Java http://flic.kr/p/4Krva2

  2. What is concurrent software? A program with more thanone thread of execution—morethan one thing happens at once! http://flic.kr/p/9ksxQa

  3. Two Units of Execution • Process • Has self-contained execution environment • Processes do not share memory (variables) • Interact via some form of message passing • Thread • AKA lightweight process • Every process has at least one (the main thread) • Faster to spawn than processes • Threads share parent processes resources (e.g., memory) • Threads interact by reading/writing variables Previously, you learned to do program processes with MPI Today, we’ll learn thread programming in Java

  4. Consider this sequential program… public class MyMain { public static int x = 0; public static int y = 0; public static void main(String[] args) { x = 10; y = x + 10; x = y; y = 0; System.out.println("x=" + x + " y=" + y); } } What result would this program give? Answer: x=20 y=0

  5. Consider this sequential program… public class MyMain { public static int x = 0; public static int y = 0; public static void main(String[] args) { x = 10; y = x + 10; x = y; y = 0; System.out.println("x=" + x + " y=" + y); } } What if you wanted these two sections to execute concurrently?

  6. Concurrent program example public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } } What result would this program give?

  7. Thread States Running Ready Blocked/Waiting Terminated

  8. Concurrent program example x = 0 y = 0 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } } Initially, the main thread runs

  9. Concurrent program example x = 0 y = 0 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } }

  10. Concurrent program example x = 0 y = 0 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } } Executing start() spawns a new threadLet’s call it T1; initially, T1 is in the Ready state

  11. Concurrent program example x = 0 y = 0 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } } Now, a context switch occurs

  12. Concurrent program example x = 0 y = 0 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } } And T1 begins executing

  13. Concurrent program example x = 10 y = 0 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } }

  14. Concurrent program example x = 10 y = 0 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } } Another context switch occurs

  15. Concurrent program example x = 10 y = 0 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } } And the main thread executes again

  16. Concurrent program example x = 0 y = 0 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } }

  17. Concurrent program example x = 0 y = 0 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } }

  18. Concurrent program example x = 0 y = 0 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } }

  19. Concurrent program example x = 0 y = 0 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } } Executing join() causes the main thread to enter the Blocking stateuntil all the threads it spawned terminate

  20. Concurrent program example x = 0 y = 0 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } }

  21. Concurrent program example x = 0 y = 10 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } }

  22. Concurrent program example x = 0 y = 10 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } } T1 finishes executing and enters the Terminated state

  23. Concurrent program example x = 0 y = 10 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } } … which causes the main thread to unblock

  24. Concurrent program example x = 0 y = 10 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } } … and eventually reenter the Running state

  25. Concurrent program example x = 0 y = 10 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } }

  26. Concurrent program example x = 0 y = 10 public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { x = 10; y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); x = y; y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } } Finally, the main thread terminates

  27. Nondeterministic scheduling increases complexity considerably and causes nasty problems public class MyMain implements Runnable { private static volatile int x = 0; private static volatile int y = 0; public void run() { A: x = 10; B: y = x + 10; } public static void main(String[] args) throws … { Thread myT = new Thread(new MyMain()); myT.start(); C: x = y; D: y = 0; myT.join(); System.out.println("x=" + x + " y=" + y); } } Race condition: Some schedules produce errors

  28. What possible results might this program return? public class MainThread { public static volatile int x = 0; public static void main(String[] args) throws … { Thread myT = new Thread(new MyThread()); if (x > 0) { x = 0; } else { x = 6; } myT.join(); System.out.println("x = " + x); } } public class MyThread implements Runnable { public void run() { MainThread.x += 5; MainThread.x -= 5; } } http://flic.kr/p/5dfuqL

  29. Let’s build a producer/consumer program!

More Related