BusyFlag.java Source code

Introduction

Here is the source code for BusyFlag.java

Source

/*
 *
 * Copyright (c) 1997-1999 Scott Oaks and Henry Wong. All Rights Reserved.
 *
 * Permission to use, copy, modify, and distribute this software
 * and its documentation for NON-COMMERCIAL purposes and
 * without fee is hereby granted.
 *
 * This sample source code is provided for example only,
 * on an unsupported, as-is basis. 
 *
 * AUTHOR MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
 * THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
 * TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE, OR NON-INFRINGEMENT. AUTHOR SHALL NOT BE LIABLE FOR
 * ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
 * DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
 *
 * THIS SOFTWARE IS NOT DESIGNED OR INTENDED FOR USE OR RESALE AS ON-LINE
 * CONTROL EQUIPMENT IN HAZARDOUS ENVIRONMENTS REQUIRING FAIL-SAFE
 * PERFORMANCE, SUCH AS IN THE OPERATION OF NUCLEAR FACILITIES, AIRCRAFT
 * NAVIGATION OR COMMUNICATION SYSTEMS, AIR TRAFFIC CONTROL, DIRECT LIFE
 * SUPPORT MACHINES, OR WEAPONS SYSTEMS, IN WHICH THE FAILURE OF THE
 * SOFTWARE COULD LEAD DIRECTLY TO DEATH, PERSONAL INJURY, OR SEVERE
 * PHYSICAL OR ENVIRONMENTAL DAMAGE ("HIGH RISK ACTIVITIES").  AUTHOR
 * SPECIFICALLY DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY OF FITNESS FOR
 * HIGH RISK ACTIVITIES.
 */

public class BusyFlag {
    protected Thread busyflag = null;
    protected int busycount = 0;

    public synchronized void getBusyFlag() {
        while (tryGetBusyFlag() == false) {
            try {
                wait();
            } catch (Exception e) {
            }
        }
    }

    public synchronized boolean tryGetBusyFlag() {
        if (busyflag == null) {
            busyflag = Thread.currentThread();
            busycount = 1;
            return true;
        }
        if (busyflag == Thread.currentThread()) {
            busycount++;
            return true;
        }
        return false;
    }

    public synchronized void freeBusyFlag() {
        if (getBusyFlagOwner() == Thread.currentThread()) {
            busycount--;
            if (busycount == 0) {
                busyflag = null;
                notify();
            }
        }
    }

    public synchronized Thread getBusyFlagOwner() {
        return busyflag;
    }
}

/*
 *
 * Copyright (c) 1997-1999 Scott Oaks and Henry Wong. All Rights Reserved.
 *
 * Permission to use, copy, modify, and distribute this software
 * and its documentation for NON-COMMERCIAL purposes and
 * without fee is hereby granted.
 *
 * This sample source code is provided for example only,
 * on an unsupported, as-is basis. 
 *
 * AUTHOR MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
 * THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
 * TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE, OR NON-INFRINGEMENT. AUTHOR SHALL NOT BE LIABLE FOR
 * ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
 * DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
 *
 * THIS SOFTWARE IS NOT DESIGNED OR INTENDED FOR USE OR RESALE AS ON-LINE
 * CONTROL EQUIPMENT IN HAZARDOUS ENVIRONMENTS REQUIRING FAIL-SAFE
 * PERFORMANCE, SUCH AS IN THE OPERATION OF NUCLEAR FACILITIES, AIRCRAFT
 * NAVIGATION OR COMMUNICATION SYSTEMS, AIR TRAFFIC CONTROL, DIRECT LIFE
 * SUPPORT MACHINES, OR WEAPONS SYSTEMS, IN WHICH THE FAILURE OF THE
 * SOFTWARE COULD LEAD DIRECTLY TO DEATH, PERSONAL INJURY, OR SEVERE
 * PHYSICAL OR ENVIRONMENTAL DAMAGE ("HIGH RISK ACTIVITIES").  AUTHOR
 * SPECIFICALLY DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY OF FITNESS FOR
 * HIGH RISK ACTIVITIES.
 */
public class CondVar {
    private BusyFlag SyncVar;

    public CondVar() {
        this(new BusyFlag());
    }

    public CondVar(BusyFlag sv) {
        SyncVar = sv;
    }

    public void cvWait() throws InterruptedException {
        cvTimedWait(SyncVar, 0);
    }

    public void cvWait(BusyFlag sv) throws InterruptedException {
        cvTimedWait(sv, 0);
    }

    public void cvTimedWait(int millis) throws InterruptedException {
        cvTimedWait(SyncVar, millis);
    }

    public void cvTimedWait(BusyFlag sv, int millis) throws InterruptedException {
        int i = 0;
        InterruptedException errex = null;

        synchronized (this) {
            // You must own the lock in order to use this method
            if (sv.getBusyFlagOwner() != Thread.currentThread()) {
                throw new IllegalMonitorStateException("current thread not owner");
            }

            // Release the lock (Completely)
            while (sv.getBusyFlagOwner() == Thread.currentThread()) {
                i++;
                sv.freeBusyFlag();
            }

            // Use wait() method        
            try {
                if (millis == 0) {
                    wait();
                } else {
                    wait(millis);
                }
            } catch (InterruptedException iex) {
                errex = iex;
            }
        }

        // Obtain the lock (Return to original state)
        for (; i > 0; i--) {
            sv.getBusyFlag();
        }

        if (errex != null)
            throw errex;
        return;
    }

    public void cvSignal() {
        cvSignal(SyncVar);
    }

    public synchronized void cvSignal(BusyFlag sv) {
        // You must own the lock in order to use this method
        if (sv.getBusyFlagOwner() != Thread.currentThread()) {
            throw new IllegalMonitorStateException("current thread not owner");
        }
        notify();
    }

    public void cvBroadcast() {
        cvBroadcast(SyncVar);
    }

    public synchronized void cvBroadcast(BusyFlag sv) {
        // You must own the lock in order to use this method
        if (sv.getBusyFlagOwner() != Thread.currentThread()) {
            throw new IllegalMonitorStateException("current thread not owner");
        }
        notifyAll();
    }
}