javaThreads multitâche en Java programmation

javaThreads multitâche en Java programmation

• 1.
  Java Threads CS 537- Introduction to Operating Systems
• 2.
  What is aThread? • Individual and separate unit of execution that is part of a process – multiple threads can work together to accomplish a common goal • Video Game example – one thread for graphics – one thread for user interaction – one thread for networking
• 3.
  What is aThread? video interaction networking Video Game Process
• 4.
  Advantages • easier toprogram – 1 thread per task • can provide better performance – thread only runs when needed – no polling to decide what to do • multiple threads can share resources • utilize multiple processors if available
• 5.
  Disadvantage • multiple threadscan lead to deadlock – much more on this later • overhead of switching between threads
• 6.
  Creating Threads (method1) • extending the Thread class – must implement the run() method – thread ends when run() method finishes – call .start() to get the thread ready to run
• 7.
  Creating Threads Example1 class Output extends Thread { private String toSay; public Output(String st) { toSay = st; } public void run() { try { for(;;) { System.out.println(toSay); sleep(1000); } } catch(InterruptedException e) { System.out.println(e); } } }
• 8.
  Example 1 (continued) classProgram { public static void main(String [] args) { Output thr1 = new Output(“Hello”); Output thr2 = new Output(“There”); thr1.start(); thr2.start(); } } • main thread is just another thread (happens to start first) • main thread can end before the others do • any thread can spawn more threads
• 9.
  Creating Threads (method2) • implementing Runnable interface – virtually identical to extending Thread class – must still define the run()method – setting up the threads is slightly different
• 10.
  Creating Threads Example2 class Output implements Runnable { private String toSay; public Output(String st) { toSay = st; } public void run() { try { for(;;) { System.out.println(toSay); Thread.sleep(1000); } } catch(InterruptedException e) { System.out.println(e); } } }
• 11.
  Example 2 (continued) classProgram { public static void main(String [] args) { Output out1 = new Output(“Hello”); Output out2 = new Output(“There”); Thread thr1 = new Thread(out1); Thread thr2 = new Thread(out2); thr1.start(); thr2.start(); } } • main is a bit more complex • everything else identical for the most part
• 12.
  Advantage of UsingRunnable • remember - can only extend one class • implementing runnable allows class to extend something else
• 13.
  Controlling Java Threads •_.start(): begins a thread running • wait() and notify(): for synchronization – more on this later • _.stop(): kills a specific thread (deprecated) • _.suspend() and resume(): deprecated • _.join(): wait for specific thread to finish • _.setPriority(): 0 to 10 (MIN_PRIORITY to MAX_PRIORITY); 5 is default (NORM_PRIORITY)
• 14.
  Java Thread Scheduling •highest priority thread runs – if more than one, arbitrary • yield(): current thread gives up processor so another of equal priority can run – if none of equal priority, it runs again • sleep(msec): stop executing for set time – lower priority thread can run
• 15.
  States of JavaThreads • 4 separate states – new: just created but not started – runnable: created, started, and able to run – blocked: created and started but unable to run because it is waiting for some event to occur – dead: thread has finished or been stopped
• 16.
  States of JavaThreads new runnable blocked dead start() stop(), end of run method wait(), I/O request, suspend() notify(), I/O completion, resume()
• 17.
  Java Thread Example1 class Job implements Runnable { private static Thread [] jobs = new Thread[4]; private int threadID; public Job(int ID) { threadID = ID; } public void run() { do something } public static void main(String [] args) { for(int i=0; i<jobs.length; i++) { jobs[i] = new Thread(new Job(i)); jobs[i].start(); } try { for(int i=0; i<jobs.length; i++) { jobs[i].join(); } } catch(InterruptedException e) { System.out.println(e); } } }
• 18.
  Java Thread Example2 class Schedule implements Runnable { private static Thread [] jobs = new Thread[4]; private int threadID; public Schedule(int ID) { threadID = ID; } public void run() { do something } public static void main(String [] args) { int nextThread = 0; setPriority(Thread.MAX_PRIORITY); for(int i=0; i<jobs.length; i++) { jobs[i] = new Thread(new Job(i)); jobs[i].setPriority(Thread.MIN_PRIORITY); jobs[i].start(); } try { for(;;) { jobs[nextThread].setPriority(Thread.NORM_PRIORITY); Thread.sleep(1000); jobs[nextThread].setPriority(Thread.MIN_PRIORITY); nextThread = (nextThread + 1) % jobs.length; } } catch(InterruptedException e) { System.out.println(e); } } }