Busy Flag
/*
*
* 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();
}
}
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