_DCE Pthreads versus NT Threads_
by Michael Yam


Listing One
/*---- testptf.cpp exercise some of PTFs classes -----*/

#include "pt\ptf.h"
#include "pt\pttf.h"

#include <stdio.h>
#include <assert.h>

// Global condition variable and counter. Program ends when gCounter <= 0.
PTTSafeType <int> gCounter;
PTCondVar gWatchEvent;

// Simple classes: increment thread, decrement thread
// and watch thread.  Uses PTObjects ctor and dtor.
class IncThread : public PTObject
{
public:
    int runPThread();
};
class DecThread : public PTObject
{
public:
    int runPThread();
};
class WatchThread : public PTObject
{
public:
    int runPThread();
};
// Implement virtual runPThread() member for all three thread classes.
int
IncThread::runPThread()
{
    while(gCounter > 0)
    {
        ++gCounter;     // thread-safe increment
        printf ("Inc Thread tid: %u  gCounter = %d\n", tid(), (int)gCounter);
#if defined (_HPUX_SOURCE) || defined (_POSIX_SOURCE)
        yield();    // HP-UX quantums can be large
#endif
    }
    return gCounter;
}
int
DecThread::runPThread()
{
    // wait for signal from watch thread before starting.
    gWatchEvent.timedWait();
    while((int)gCounter > 0)
    {
        --gCounter; // thread-safe decrement
        printf ("Dec Thread tid: %u  gCounter = %d\n", tid(), (int)gCounter);
#if defined (_HPUX_SOURCE) || defined (_POSIX_SOURCE)
        yield();    // HP-UX quantums can be large
#endif
    }
    return gCounter;
}
int
WatchThread::runPThread()
{
    PTCondVar sleepEvent;
    DecThread decThread1;
    DecThread decThread2;
    // threads are started but not yet signaled.
    decThread1.start();
    decThread2.start();

    while((int)gCounter > 0)
    {
        printf ("Watch Thread tid: %u  gCounter = %d\n", tid(), (int)gCounter);
        if (gCounter > 1000)
        {
            // wake one dec thread if counter is over arbitrary limit.
            gWatchEvent.signal();
        }
        sleepEvent.timedWait (3);   // nap for 3 secs
    }
    decThread1.join();
    decThread2.join();

    return gCounter;
}
int main()
{
    gCounter = 500;     // arbitrary start count;

    IncThread incThread;
    WatchThread watchThread;

    if (watchThread.isValid())
        watchThread.start();
    if (incThread.isValid())
        incThread.start();
    watchThread.join();
    incThread.join();

    printf ("gCounter = %d\n", (int)gCounter);

    return 0;
}