Qfyilyi

We have 10 drivers, 10 cars and 100 students. Each driver has a car and these cars can take up to four students. The cars will leave the taxi stop only if its full. In an empty car, the driver will always sleep. If a student enters the car, student will wake the driver and driver will make a call for empty seats.

In my code, i can't seem to make driver wait for the car to be full. When a student wakes driver, driver leaves immediately without waiting other students.

We want drivers to wait for cars to be full to leave the taxi stop. How can it be done?

#include <stdio.h>

#include <unistd.h>

#include <stdlib.h>

#include <stdio.h>

#include <unistd.h>

#include <stdlib.h>

#include <pthread.h>

#include <semaphore.h> 



// The maximum number of customer threads.

#define MAX_STUDENTS 100





void *student(void *num);

void *driver(void *);

void randwait(int secs);









//Define the semaphores.

// waitingDriver Limits the # of drivers allowed  to drive a taxi.

sem_t waitingDriver;

// taxiChair ensures mutually exclusive access to the taxi chair.

sem_t taxiChair;

// driverPillow is used to allow the driver to sleep until a student arrives.

sem_t driverPillow;

// seatBelt is used to make the students to wait until the driver is done driving.

sem_t seatBelt;

// Flag to stop the driver thread when all students have been serviced.

int allDone = 0;





int main(int argc, char *argv)

{

    pthread_t dtid[10];

    pthread_t stid[MAX_STUDENTS];

    int i, x, numStudents, numDrivers = 1, numChairs = 4; int Number[MAX_STUDENTS];

    printf("Maximum number of customers can only be 100. Enter number of students.n");

    scanf("%d",&x);

    numStudents = x;

    if (numStudents > MAX_STUDENTS) {

        printf("The maximum number of Students is %d.n", MAX_STUDENTS);

        system("PAUSE");   

        return 0;

    }

    printf("A solution to the taxi problem using semaphores.n");

    for (i = 0; i < MAX_STUDENTS; i++) {

        Number[i] = i;

    }

    // Initialize the semaphores with initial values...

    sem_init(&waitingDriver, 0, 10);

    sem_init(&taxiChair, 0, 4);

    sem_init(&driverPillow, 0, 0);

    sem_init(&seatBelt, 0, 4);



    // Create the taxis.

    for (i = 0; i < numDrivers; i++) {

        pthread_create(&dtid[i], NULL, driver, (void *)&Number[i+1]);

    }



        // Create the customers.

    for (i = 0; i < numStudents; i++) {

        pthread_create(&stid[i], NULL, student, (void *)&Number[i+1]);

    }

        // Join each of the threads to wait for them to finish.

    for (i = 0; i < numStudents; i++) {

        pthread_join(stid[i],NULL);

    }

        // When all of the customers are finished, kill the barber thread.

    allDone = 1;

    sem_post(&driverPillow); // Wake the barber so he will exit.

    for (i = 0; i < numDrivers; i++) {

        pthread_join(dtid[i],NULL);

    }

    system("PAUSE");   

    return 0;

}





void *student(void *number) {

     int num = *(int *)number; // Leave for the taxispot and take some random amount of  time to arrive.

     printf("Student %d leaving for taxi.n", num);

     randwait(5);

    printf("Student %d arrived at taxi.n", num); // Wait for space to open up in the waiting room...

     sem_wait(&waitingDriver);

     printf("Student %d entering taxi.n", num); // Wait for the taxi driver to become free.

     sem_wait(&taxiChair); // The chair is free so give up your spot in the  taxispot.

     sem_post(&waitingDriver); // Wake up the driver...

     printf("Student %d waking the driver.n", num);

     sem_post(&driverPillow); // Wait for the driver to finish circuit.

     sem_wait(&seatBelt); // Give up the chair.

     sem_post(&taxiChair);

     printf("Student %d leaving taxi.n", num);

}



void *driver(void *number)

{

    int num = *(int *)number; // Leave for the taxi and take some random amount of  time to arrive.

    while (!allDone) { // Sleep until someone arrives and wakes you..

        printf("The driver %d is sleepingn", num);

            sem_wait(&driverPillow); // Skip this stuff at the end...

            if (!allDone)

            { // Take a random amount of time to drive the students.

                printf("The driver %d is drivingn", num);

                randwait(3);

                printf("The driver %d has finished circuit.n", num); // Release the students when done driving...

                sem_post(&seatBelt);

            }

            else {

                printf("The driver %d is going home for the day.n", num);

            }

    }

}





void randwait(int secs) {

     int len = 1; // Generate an arbit number...

     sleep(len);

}