testsem.java

介绍有关java的资料 课件 相当一本书籍 里面都是很基础的知识

		class Semaphore {
		    final static int EMPTY = 0;
		    final static int READING = 1;
		    final static int WRITING = 2;
		    protected int state = EMPTY;
		    protected int readCnt = 0;
		    public synchronized void readLock() {
		        if(state == EMPTY) {
		            state = READING;
		        }
		        else if(state == READING) {}
		        else if(state == WRITING) {
		            while(state == WRITING) {
		                try{
		                    wait();
		                }catch(Exception e){}
		            }
		            state = READING;
		        }
		        readCnt++;
		        return;
		    }
		    public synchronized void writeLock() {
		        if(state == EMPTY) {
		            state = WRITING;
		        }
		        else {
		            while(state != EMPTY) {
		                try{
		                    wait();
		                }catch(Exception e){}
		            }
		        }
		    }
		    public synchronized void readUnlock() {
		        readCnt--;
		        if(readCnt == 0) {
		            state = EMPTY;
		            notify();
		        }
		    }
		    public synchronized void writeUnlock() {
		        state = EMPTY;
		        notify();
		    }
		}
		class process extends Thread {
		    String op;
		    Semaphore sem;
		    process(String name,String op,Semaphore sem) {
		        super(name);
		        this.op = op;
		        this.sem = sem;
		        start();
		    }
		    public void run() {
		        if(op.compareTo("read") == 0) {
		            System.out.println("Try to get readLock"+getName());
		            sem.readLock();
		            System.out.println("Read op:"+getName());
		            try{
		                sleep((int)Math.random()*50);
		            }catch(Exception e){}
		            System.out.println("Unlocking readLock:"+getName());
		            sem.readUnlock();
		        }
		        else if(op.compareTo("write") == 0) {
		            System.out.println("Try to get writeLock"+getName());
		            sem.writeLock();
		            System.out.println("Write op:"+getName());
		            try{
		                sleep((int)Math.random()*50);
		            }catch(Exception e){}
		            System.out.println("Unlocking writeLock:"+getName());
		            sem.writeUnlock();
		        }
		    }
		}
		public class testSem {
		    public static void main(String argv[]) {
		        Semaphore lock = new Semaphore();
		        new process("1","read",lock);
		        new process("2","read",lock);
		        new process("3","write",lock);
		        new process("4","read",lock);
		    }
		}