The signal() function wakes up a thread waiting for the Condition object
There may be multiple threads waiting for the same condition object
You need to use broadcast() instead of signal() to wake up these threads
Robot assembly line for automobile manufacturing
Each Car will be assembled in several stages
//: C11:CarBuilder.cpp {RunByHand}
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// How broadcast() works.
//{L} ZThread
#include <iostream>
#include <string>
#include "zthread/Thread.h"
#include "zthread/Mutex.h"
#include "zthread/Guard.h"
#include "zthread/Condition.h"
#include "zthread/ThreadedExecutor.h"
#include "TQueue.h"
using namespace ZThread;
using namespace std;
class Car {
int id;
bool engine, driveTrain, wheels;
public:
Car(int idn) : id(idn), engine(false),
driveTrain(false), wheels(false) {}
// Empty Car object:
Car() : id(-1), engine(false),
driveTrain(false), wheels(false) {}
// Unsynchronized -- assumes atomic bool operations:
int getId() { return id; }
void addEngine() { engine = true; }
bool engineInstalled() { return engine; }
void addDriveTrain() { driveTrain = true; }
bool driveTrainInstalled() { return driveTrain; }
void addWheels() { wheels = true; }
bool wheelsInstalled() { return wheels; }
friend ostream& operator<<(ostream& os, const Car& c) {
return os << "Car " << c.id << " ["
<< " engine: " << c.engine
<< " driveTrain: " << c.driveTrain
<< " wheels: " << c.wheels << " ]";
}
};
typedef CountedPtr< TQueue<Car> > CarQueue;
class ChassisBuilder : public Runnable {
CarQueue carQueue;
int counter;
public:
ChassisBuilder(CarQueue& cq) : carQueue(cq),counter(0) {}
void run() {
try {
while(!Thread::interrupted()) {
Thread::sleep(1000);
// Make chassis:
Car c(counter++);
cout << c << endl;
// Insert into queue
carQueue->put(c);
}
} catch(Interrupted_Exception&) { /* Exit */ }
cout << "ChassisBuilder off" << endl;
}
};
class Cradle {
Car c; // Holds current car being worked on
bool occupied;
Mutex workLock, readyLock;
Condition workCondition, readyCondition;
bool engineBotHired, wheelBotHired, driveTrainBotHired;
public:
Cradle()
: workCondition(workLock), readyCondition(readyLock) {
occupied = false;
engineBotHired = true;
wheelBotHired = true;
driveTrainBotHired = true;
}
void insertCar(Car chassis) {
c = chassis;
occupied = true;
}
Car getCar() { // Can only extract car once
if(!occupied) {
cerr << "No Car in Cradle for getCar()" << endl;
return Car(); // "Null" Car object
}
occupied = false;
return c;
}
// Access car while in cradle:
Car* operator->() { return &c; }
// Allow robots to offer services to this cradle:
void offerEngineBotServices() {
Guard<Mutex> g(workLock);
while(engineBotHired)
workCondition.wait();
engineBotHired = true; // Accept the job
}
void offerWheelBotServices() {
Guard<Mutex> g(workLock);
while(wheelBotHired)
workCondition.wait();
wheelBotHired = true; // Accept the job
}
void offerDriveTrainBotServices() {
Guard<Mutex> g(workLock);
while(driveTrainBotHired)
workCondition.wait();
driveTrainBotHired = true; // Accept the job
}
// Tell waiting robots that work is ready:
void startWork() {
Guard<Mutex> g(workLock);
engineBotHired = false;
wheelBotHired = false;
driveTrainBotHired = false;
workCondition.broadcast();
}
// Each robot reports when their job is done:
void taskFinished() {
Guard<Mutex> g(readyLock);
readyCondition.signal();
}
// Director waits until all jobs are done:
void waitUntilWorkFinished() {
Guard<Mutex> g(readyLock);
while(!(c.engineInstalled() && c.driveTrainInstalled()
&& c.wheelsInstalled()))
readyCondition.wait();
}
};
typedef CountedPtr<Cradle> CradlePtr;
class Director : public Runnable {
CarQueue chassisQueue, finishingQueue;
CradlePtr cradle;
public:
Director(CarQueue& cq, CarQueue& fq, CradlePtr cr)
: chassisQueue(cq), finishingQueue(fq), cradle(cr) {}
void run() {
try {
while(!Thread::interrupted()) {
// Blocks until chassis is available:
cradle->insertCar(chassisQueue->get());
// Notify robots car is ready for work
cradle->startWork();
// Wait until work completes
cradle->waitUntilWorkFinished();
// Put car into queue for further work
finishingQueue->put(cradle->getCar());
}
} catch(Interrupted_Exception&) { /* Exit */ }
cout << "Director off" << endl;
}
};
class EngineRobot : public Runnable {
CradlePtr cradle;
public:
EngineRobot(CradlePtr cr) : cradle(cr) {}
void run() {
try {
while(!Thread::interrupted()) {
// Blocks until job is offered/accepted:
cradle->offerEngineBotServices();
cout << "Installing engine" << endl;
(*cradle)->addEngine();
cradle->taskFinished();
}
} catch(Interrupted_Exception&) { /* Exit */ }
cout << "EngineRobot off" << endl;
}
};
class DriveTrainRobot : public Runnable {
CradlePtr cradle;
public:
DriveTrainRobot(CradlePtr cr) : cradle(cr) {}
void run() {
try {
while(!Thread::interrupted()) {
// Blocks until job is offered/accepted:
cradle->offerDriveTrainBotServices();
cout << "Installing DriveTrain" << endl;
(*cradle)->addDriveTrain();
cradle->taskFinished();
}
} catch(Interrupted_Exception&) { /* Exit */ }
cout << "DriveTrainRobot off" << endl;
}
};
class WheelRobot : public Runnable {
CradlePtr cradle;
public:
WheelRobot(CradlePtr cr) : cradle(cr) {}
void run() {
try {
while(!Thread::interrupted()) {
// Blocks until job is offered/accepted:
cradle->offerWheelBotServices();
cout << "Installing Wheels" << endl;
(*cradle)->addWheels();
cradle->taskFinished();
}
} catch(Interrupted_Exception&) { /* Exit */ }
cout << "WheelRobot off" << endl;
}
};
class Reporter : public Runnable {
CarQueue carQueue;
public:
Reporter(CarQueue& cq) : carQueue(cq) {}
void run() {
try {
while(!Thread::interrupted()) {
cout << carQueue->get() << endl;
}
} catch(Interrupted_Exception&) { /* Exit */ }
cout << "Reporter off" << endl;
}
};
int main() {
cout << "Press <Enter> to quit" << endl;
try {
CarQueue chassisQueue(new TQueue<Car>),
finishingQueue(new TQueue<Car>);
CradlePtr cradle(new Cradle);
ThreadedExecutor assemblyLine;
assemblyLine.execute(new EngineRobot(cradle));
assemblyLine.execute(new DriveTrainRobot(cradle));
assemblyLine.execute(new WheelRobot(cradle));
assemblyLine.execute(
new Director(chassisQueue, finishingQueue, cradle));
assemblyLine.execute(new Reporter(finishingQueue));
// Start everything running by producing chassis:
assemblyLine.execute(new ChassisBuilder(chassisQueue));
cin.get();
assemblyLine.interrupt();
} catch(Synchronization_Exception& e) {
cerr << e.what() << endl;
}
getchar();
} ///:~output
ThreadQueue created
Press <Enter> to quit
User thread created.
Reference thread created.
1 reference-thread added.
pollPendingThreads()
1 user-thread added.
Thread starting...
User thread created.
pollPendingThreads()
1 user-thread added.
Thread starting...
User thread created.
pollPendingThreads()
1 user-thread added.
Thread starting...
User thread created.
pollPendingThreads()
1 user-thread added.
Thread starting...
User thread created.
pollPendingThreads()
1 user-thread added.
Thread starting...
User thread created.
pollPendingThreads()
1 user-thread added.
Thread starting...
Car 0 [ engine: 0 driveTrain: 0 wheels: 0 ]
Installing engine
Installing DriveTrain
Installing Wheels
Car 0 [ engine: 1 driveTrain: 1 wheels: 1 ]
Car 1 [ engine: 0 driveTrain: 0 wheels: 0 ]
Installing Wheels
Installing engine
Installing DriveTrain
Car 1 [ engine: 1 driveTrain: 1 wheels: 1 ]
Car 2 [ engine: 0 driveTrain: 0 wheels: 0 ]
Installing engine
Installing Wheels
Installing DriveTrain
Car 2 [ engine: 1 driveTrain: 1 wheels: 1 ]
Car 3 [ engine: 0 driveTrain: 0 wheels: 0 ]
Installing Wheels
Installing engine
Installing DriveTrain
Car 3 [ engine: 1 driveTrain: 1 wheels: 1 ]
Car 4 [ engine: 0 driveTrain: 0 wheels: 0 ]
Installing DriveTrain
Installing Wheels
Installing engine
Car 4 [ engine: 1 driveTrain: 1 wheels: 1 ]
Car 5 [ engine: 0 driveTrain: 0 wheels: 0 ]
Installing DriveTrain
Installing engine
Installing Wheels
Car 5 [ engine: 1 driveTrain: 1 wheels: 1 ]
Car 6 [ engine: 0 driveTrain: 0 wheels: 0 ]
Installing engine
Installing DriveTrain
Installing Wheels
Car 6 [ engine: 1 driveTrain: 1 wheels: 1 ]
Car 7 [ engine: 0 driveTrain: 0 wheels: 0 ]
Installing Wheels
Installing engine
Installing DriveTrain
Car 7 [ engine: 1 driveTrain: 1 wheels: 1 ]
Car 8 [ engine: 0 driveTrain: 0 wheels: 0 ]
Installing Wheels
Installing engine
Installing DriveTrain
Car 8 [ engine: 1 driveTrain: 1 wheels: 1 ]
Car 9 [ engine: 0 driveTrain: 0 wheels: 0 ]
Installing engine
Installing Wheels
Installing DriveTrain
Car 9 [ engine: 1 driveTrain: 1 wheels: 1 ]
Car 10 [ engine: 0 driveTrain: 0 wheels: 0 ]
Installing DriveTrain
Installing engine
Installing Wheels
Car 10 [ engine: 1 driveTrain: 1 wheels: 1 ]
Car 11 [ engine: 0 driveTrain: 0 wheels: 0 ]
Installing Wheels
Installing DriveTrain
Installing engine
Car 11 [ engine: 1 driveTrain: 1 wheels: 1 ]
Car 12 [ engine: 0 driveTrain: 0 wheels: 0 ]
Installing DriveTrain
Installing engine
Installing Wheels
Car 12 [ engine: 1 driveTrain: 1 wheels: 1 ]
Car took a short cut:
Suppose the Boolean operation is an atom
Each Car starts with a raw chassis
Different robots assemble different parts of it