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Concurrency in Java: Lecture Notes from CMPSCI 691W, Spring 2006, Study notes of Computer Science

University of Massachusetts - AmherstComputer Science

Material Type: Notes; Class: S-Gen Purpose Cmptn-GPU; Subject: Computer Science; University: University of Massachusetts - Amherst; Term: Spring 2006;

Typology: Study notes

Pre 2010

Uploaded on 08/19/2009

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koofers-user-s7p 🇺🇸

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CMPSCI 691W Parallel and Concurrent Programming Spring 2006
Lecture 4: February 13
Lecturer: Emery Berger Scribe: Matthew Marzilli
4.1 Concurrency in Java
•Unlike C/C++, Java has built in concurrency support;
•Various concurrency patterns available.
4.1.1 Java Objects and Concurrency
•Every Java Object has a lock
•Very convenient! but obvious space overhead
•Can always lock an object with synchronized reserved word
•JVM implements ’thin locks’, status bit with every object, 0 or 1, only 1 if ever locked
•Benefit+ No accidental double locking
•Benefit+ Unlocks implicit, these are Scoped Locks
•Benefit+ Thread specific data becomes private local data to object
4.1.2 Built in CV
•obj.wait();
•obj.wait(long timeout);
•obj.notify();
•obj.notifyall();
4.1.3 Using Java Threads
•Simply Extend Thread;
•implement run() method;
•call start() on the object;
•Each thread has name, priority, and more: http://java.sun.com/j2se/1.3/docs/api/java/lang/Thread.html;
4-1
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Download Concurrency in Java: Lecture Notes from CMPSCI 691W, Spring 2006 and more Study notes Computer Science in PDF only on Docsity!

CMPSCI 691W Parallel and Concurrent Programming Spring 2006

Lecture 4: February 13

Lecturer: Emery Berger Scribe: Matthew Marzilli

4.1 Concurrency in Java

  • Unlike C/C++, Java has built in concurrency support;
  • Various concurrency patterns available.

4.1.1 Java Objects and Concurrency

  • Every Java Object has a lock
  • Very convenient! but obvious space overhead
  • Can always lock an object with synchronized reserved word
  • JVM implements ’thin locks’, status bit with every object, 0 or 1, only 1 if ever locked
  • Benefit+ No accidental double locking
  • Benefit+ Unlocks implicit, these are Scoped Locks
  • Benefit+ Thread specific data becomes private local data to object

4.1.2 Built in CV

  • obj.wait();
  • obj.wait(long timeout);
  • obj.notify();
  • obj.notifyall();

4.1.3 Using Java Threads

  • Simply Extend Thread;
  • implement run() method;
  • call start() on the object;
  • Each thread has name, priority, and more: http://java.sun.com/j2se/1.3/docs/api/java/lang/Thread.html;

4-2 Lecture 4: February 13

4.1.4 Note on Priority

  • Unlike UNIX, higher priority == higher value!;
  • setPriority(int), getPriority(), example setPriority(Thread.MAX PRIORITY)
  • If any thread is runnable at level i, run instead of any thread less than i
  • Fixed priority scheduling, although not guaranteed to always hold Use for performance reasons, NOT safety
  • Java will not change priority levels on you

4.2 Concurrency and Java 1.5 aka ’Tiger’

  • Built on Doug Lea’s concurrency library;

4.2.1 More Concurrency Constructs

  • Semaphores Ordinary counting acquire(), tryAcquire(), release() Fair (FIFO) ordering
  • Linked Blocking Queue Blocks on put() if full, Blocks on take() if empty Allows for producer consumer threads to add and remove work from a shared structure Linked implementation, queue does not need a limit Does allow for max capacity WebServer example, through put declines after some number of clients Solution: Use Blocking Queue, reject new clients by setting capacity of pipeline
  • Array Blocking Queue Blocks on put() if full, Blocks on take() if empty Same idea, except an array implementation Ideal for fixed number of tasks
  • Synchornus Queue Each put() waits for a take(), Also called a Rendezvous channel If you come back from a put() you can be sure there was a take() CSP - Communicating Sequential Processes Tony Hoare, inspired a language called OCCAM
  • Priority Blocking Queue Unbounded Queue, based on heap Head = item with ’lowest priority’ Useful for concurrent simulation applications

4-4 Lecture 4: February 13

4.4 Further Links

  • Concurrent Java 1.5 Package Listing http://java.sun.com/j2se/1.5.0/docs/api/java/util/concurrent/package-summary.html
  • Info about OCCAM http://www.wotug.org/occam/
  • Original Slides for this lecture: http://www.cs.umass.edu/ emery/classes/cmpsci691w-spring2006/lectures/cmpsci691w-lecture04- java.pdf