multithread synchronization using semaphore

 

#include <iostream>

#include<pthread.h>

#include<semaphore.h>

using namespace std;

pthread_t t[5];

sem_t sem[5];

int c = 0;

#define NUM 30

void* inc(void* p)

{

    while(c < NUM)

    {

        if(sem_wait(&sem[0]) == 0)

        {

            cout<<"T0 inc:"<<++c<<endl;

            sem_post(&sem[1]);

        }

    }

    

    pthread_exit(NULL);

}

void* odd(void* p)

{

    while(c < NUM)

    {

        if (sem_wait(&sem[1]) == 0)

        {

            if (0 != c % 2)

            {

                cout<<c<<":T1 odd"<<endl;

            }

            sem_post(&sem[2]);

        }

    }

    

    pthread_exit(NULL);

}

void* even(void* p)

{

    while(c < NUM)

    {

        if (sem_wait(&sem[2]) == 0)

        {

            if (0 == c % 2)

            {

                cout<<c<<":T2 even"<<endl;

            }

            sem_post(&sem[3]);

        }

    }

    

    pthread_exit(NULL);

}

void* mul2(void* p)

{

    while(c < NUM)

    {

        if (sem_wait(&sem[3]) == 0)

        {

            if (0 == c % 2)

            {

                cout<<c<<": T3 mul by 2"<<endl;

            }

            sem_post(&sem[4]);

        }

    }

    

    pthread_exit(NULL);

}

void* mul5(void* p)

{

    while(c < NUM)

    {

        if (sem_wait(&sem[4]) == 0)

        {

            if (0 == c % 5)

            {

                cout<<c<<": T4 mul by 5"<<endl;

            }

            sem_post(&sem[0]);

        }

    }

    

    pthread_exit(NULL);

}

int main()

{

    sem_init(&sem[0], 0, 1);

    sem_init(&sem[1], 0, 0);

    sem_init(&sem[2], 0, 0);

    sem_init(&sem[3], 0, 0);

    sem_init(&sem[4], 0, 0);

    pthread_create(&t[0], NULL, &inc, NULL);

    pthread_create(&t[1], NULL, &odd, NULL);

    pthread_create(&t[2], NULL, &even, NULL);

    pthread_create(&t[3], NULL, &mul2, NULL);

    pthread_create(&t[4], NULL, &mul5, NULL);

    pthread_join(t[0], NULL);

    pthread_join(t[1], NULL);

    pthread_join(t[2], NULL);

    pthread_join(t[3], NULL);

    pthread_join(t[4], NULL);

    

    pthread_exit(NULL);

    return 0;

}

OpenCV convolution

  Convolution is general purpose filter for image processing where center pixel and its neighboring pixels gets multiplied with a matrix i.e kernel 

some example of kernel:

 

OpenCV does convolution using filter2D function. 

The basic usage is given below.

void cv::filter2D   (   InputArray  src,
OutputArray     dst,
int     ddepth,
InputArray  kernel,
Point   anchor = Point(-1,-1),
double  delta = 0,
int     borderType = BORDER_DEFAULT 
)

where, 

• src is input image.
• dst is output image of the same size and the same number of channels as src.
• ddepth is desired depth of the destination image.
• kernel is convolution kernel, a single-channel floating point matrix; i
• anchor anchor of the kernel that indicates the relative position of a filtered point within the kernel; the anchor should lie within the kernel; default value (-1,-1) means that the anchor is at the kernel center.
• delta optional value added to the filtered pixels before storing them in dst.
• borderType pixel extrapolation method.

// Result image 
Mat result; 

// Apply convolution
filter2D(image, result, -1 , kernel, Point(-1, -1), 0, BORDER_DEFAULT);