I want to use Eigen
library as my shared memory data structure (by mmap
).
here is my code:
producer.cpp:
#include<sys/mman.h>
#include<sys/types.h>
#include<fcntl.h>
#include<string.h>
#include<stdio.h>
#include<unistd.h>
#include <vector>
#include <iostream>
#include <string>
#include "eigen3/Eigen/Dense"
typedef Eigen::Matrix<double, Eigen::Dynamic, Eigen::Dynamic, Eigen::ColMajor> eigen_matrix;
using namespace std;
int main(int argc,char **argv) {
int fd = open(argv[1], O_CREAT | O_RDWR | O_TRUNC, 0777);
size_t size = 100 * 100 * sizeof(typename eigen_matrix::Scalar);
lseek(fd, size, SEEK_SET);
write(fd,"",1);
eigen_matrix* p =(eigen_matrix*)mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
p->resize(100, 100);
(*p)(0, 0) = 1;
double s;
size_t count = 0;
while (std::cin >> s && s != 0) {
(*p)(count , 0) = s;
}
printf("initialize over\n");
munmap(p, size);
close(fd);
}
consumer.cpp:
#include<sys/mman.h>
#include<sys/types.h>
#include<fcntl.h>
#include<string.h>
#include<stdio.h>
#include<unistd.h>
#include <vector>
#include <iostream>
#include <string>
#include "eigen3/Eigen/Dense"
using namespace std;
typedef Eigen::Matrix<double, Eigen::Dynamic, Eigen::Dynamic, Eigen::ColMajor> eigen_matrix;
int main(int argc,char **argv) {
int fd = open(argv[1], O_RDWR, 0777);
size_t size = 100 * 100 * sizeof(typename eigen_matrix::Scalar);
lseek(fd, size, SEEK_SET);
eigen_matrix* p = (eigen_matrix*)mmap(NULL, size, PROT_READ, MAP_SHARED, fd, 0);
close(fd);
printf("%zu %zu\n", p->cols(), p->rows());
cout << *p <<endl; // here crashed !!
std::string s;
while (std::cin >> s && s != "quit") {
cout << *p << endl;
}
munmap(p, size);
}
As you can see in the code, consumer crashed on
cout << *p << endl;
could you help on this? Is there anything i ignored?
CodePudding user response:
Dynamic Eigen matrices are like std::vector. They don't hold the actual data, they contain pointers to the data plus the size information. You mmapped the object, not the actual data.
Something like this should work:
Eigen::Index rows = 100, cols = 100;
const void* space = mmap(NULL, rows * cols * sizeof(double),
PROT_READ, MAP_SHARED, fd, 0);
Eigen::MatrixXd::ConstMapType mapped = Eigen::MatrixXd::Map(
static_cast<const double*>(space), rows, cols);