I need to write a simple program: There will be a Parent and a few programs [children] (started via execl in Parent). Children communicate to one another in this way: Child I sens to Parent number J, Parent sends a message (something like -- "there is a message to you") to J, J send to Parent number K etc. etc.
And there is a problem -- my program (tested by strace command) tries to send a message to child and there comes the broken pipe error.
I will be grateful if somebody looks through the code and tells me what's wrong:
Here is the code:
/**
* Arbiter zabawy w Losia
*
wersja: Alfa 3b
początek edycji 25.01.2009
*/
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include "err.h"
pid_t pid;
FILE *a;
int main ()
{
// my N players
int N;
N = 10;
//write -- writing from parent to child
//read -- reading from child
int rurka_write[N+1][2];
int rurka_read[N+1][2];
//initiation of N players
int i;
for(i = 1; i <= N; i++)
{
//tworze lacza
if (pipe(rurka_write[i]) == -1)
printf("wystapil blad przy rurce %d\n", i);
if (pipe(rurka_read[i]) == -1)
printf("wystapil blad przy rurce %d\n", i);
}
for(i = 1; i <= N; i++)
{
switch(pid = fork())
{
case -1:
printf("wystapil blad przy forkowaniu");
case 0:
printf("potomek numer %d\n", i);
if (close(rurka_write[i][1]) == -1)
printf("zle zamykanie");
if (close(rurka_read[i][0]) == -1)
printf("zle zamykanie");
//closing useless descriptors
int j;
for(j = 1; j <= N; j++)
{
if (j != i)
{
close(rurka_read[j][0]);
close(rurka_read[j][1]);
close(rurka_write[j][0]);
close(rurka_write[j][1]);
}
}
char str_N[20];
char str_i[20];
char str_0[20];
char str_1[20];
sprintf(str_N, "%d", N);
sprintf(str_i, "%d", i);
sprintf(str_0, "%d", rurka_write[i][0]);
sprintf(str_1, "%d", rurka_read[i][1]);
printf("%d Executing execl\n", i);
execl("./ucz", str_N, str_i, str_0, str_1, NULL);
printf("execl executed\n");
// execv("./ucz", str_N, str_i, str_0, str_1, NULL);
//exit(0);
default:
//closing useless pipes
if (close(rurka_read[i][1]) == -1)
printf("zle zamykanie rurki do czytania z potomkna\n");
if (close(rurka_write[i][0]) == -1)
printf("zle zamykanie rurki do pisania do potomka\n");
} //end of switch
} //end of for
//if I am in parent, I'm starting the game
if (pid != 0)
// delay(100);
{
printf("PLAY\n");
int l = 1;
while(l > 0)
{
printf("sending to player %d\n", l);
a = fdopen(rurka_write[l][1], "w");
printf("sending: Wake up");
fprintf(a, "Wake up\n");
printf("flushing");
fflush(a);
char k[20];
printf("reading");
read(rurka_read[l][0], k, 20);
l = k;
}
}
}
Besides the fact that you do not end your cases with a break (as noted by strager), the main problem is the statement l = k;. Note that k is a char[20] and, when assigned to a int, you don't assign any of the contents of k to l. Instead l will contain (the value of) the pointer to the array. You will have to do something different here to get the value that is in the array; what exactly depends on that ucz sends back.
After fixing this and making my own ucz, the program seems to work without any problem. Of course, it might also be that there is another problem in your version of ucz.
About ./ucz -- it takes 4 parameters -- 1st -- number of players, 2nd -- player number, 3rd -- number of descriptor to read from parent, 4th -- number of descriptor to write to parent.
Adding exit(0), return(0), break after exec (or in the end of "case: 0") doesn't help.
Related
Please Help!
I am using MPI (= Message Passing Interface) in python for a ring communication, which means that every rank are sending and receiving from each other. I know one way to realize this is by using for instance MPI.COMM_WORLD.issend()and MPI.COMM_WORLD.recv(), this is working and done.
Now I want to realize the same Output on a different way by using MPI.Topocomm.Neighbor_alltoallw but this is not working. I wrote a C Code and is working there, so the same output can be reached with this function, but when I implement this in python it is not working. Please find below the C Code and the Python Code
The definition of the Function says (mpi4py Package for Python):
Neighbor_alltoallw(...)
Topocomm.Neighbor_alltoallw(self, sendbuf, recvbuf)
Neighbor All-to-All Generalized
I do not understand following things:
why is recbuf not a return value? it seems to be an argument here
how can this be implmented for a ring communication in Python?
Thank you for your time and support!
my working C Code:
#include <stdio.h>
#include <mpi.h>
#define to_right 201
#define max_dims 1
int main (int argc, char *argv[])
{
int my_rank, size;
int snd_buf, rcv_buf;
int right, left;
int sum, i;
MPI_Comm new_comm;
int dims[max_dims],
periods[max_dims],
reorder;
MPI_Aint snd_displs[2], rcv_displs[2];
int snd_counts[2], rcv_counts[2];
MPI_Datatype snd_types[2], rcv_types[2];
MPI_Status status;
MPI_Request request;
MPI_Init(&argc, &argv);
/* Get process info. */
MPI_Comm_size(MPI_COMM_WORLD, &size);
/* Set cartesian topology. */
dims[0] = size;
periods[0] = 1;
reorder = 1;
MPI_Cart_create(MPI_COMM_WORLD, max_dims, dims, periods,
reorder,&new_comm);
/* Get coords */
MPI_Comm_rank(new_comm, &my_rank);
/* MPI_Cart_coords(new_comm, my_rank, max_dims, my_coords); */
/* Get nearest neighbour rank. */
MPI_Cart_shift(new_comm, 0, 1, &left, &right);
/* Compute global sum. */
sum = 0;
snd_buf = my_rank;
rcv_buf = -1000; /* unused value, should be overwritten by first MPI_Recv; only for test purpose */
rcv_counts[0] = 1; MPI_Get_address(&rcv_buf, &rcv_displs[0]); snd_types[0] = MPI_INT;
rcv_counts[1] = 0; rcv_displs[1] = 0 /*unused*/; snd_types[1] = MPI_INT;
snd_counts[0] = 0; snd_displs[0] = 0 /*unused*/; rcv_types[0] = MPI_INT;
snd_counts[1] = 1; MPI_Get_address(&snd_buf, &snd_displs[1]); rcv_types[1] = MPI_INT;
for( i = 0; i < size; i++)
{
/* Substituted by MPI_Neighbor_alltoallw() :
MPI_Issend(&snd_buf, 1, MPI_INT, right, to_right,
new_comm, &request);
MPI_Recv(&rcv_buf, 1, MPI_INT, left, to_right,
new_comm, &status);
MPI_Wait(&request, &status);
*/
MPI_Neighbor_alltoallw(MPI_BOTTOM, snd_counts, snd_displs, snd_types,
MPI_BOTTOM, rcv_counts, rcv_displs, rcv_types, new_comm);
snd_buf = rcv_buf;
sum += rcv_buf;
}
printf ("PE%i:\tSum = %i\n", my_rank, sum);
MPI_Finalize();
}
My not working Python Code:
from mpi4py import MPI
size = MPI.COMM_WORLD.Get_size()
my_rank = MPI.COMM_WORLD.Get_rank()
to_right =201
max_dims=1
dims = [max_dims]
periods=[max_dims]
dims[0]=size
periods[0]=1
reorder = True
new_comm=MPI.Intracomm.Create_cart(MPI.COMM_WORLD,dims,periods,True)
my_rank= new_comm.Get_rank()
left_right= MPI.Cartcomm.Shift(new_comm,0,1)
left=left_right[0]
right=left_right[1]
sum=0
snd_buf=my_rank
rcv_buf=-1000 #unused value, should be overwritten, only for test purpose
for counter in range(0,size):
MPI.Topocomm.Neighbor_alltoallw(new_comm,snd_buf,rcv_buf)
snd_buf=rcv_buf
sum=sum+rcv_buf
print('PE ', my_rank,'sum=',sum)
Threaded quick sort method:
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include "MD5.h"
#include <thread>
using namespace std;
template<typename T>
void quickSort(vector<T> &arr, int left, int right) {
int i = left, j = right; //Make local copys to modify
T tmp; //Termorary variable to use for swaping.
T pivot = arr[(left + right) / 2]; //Find the centerpoint. if 0.5 truncate.
while (i <= j) {
while (arr[i] < pivot) //is i < pivot?
i++;
while (arr[j] > pivot) //Is j > pivot?
j--;
if (i <= j) { //Swap
tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
i++;
j--;
}
};
thread left_t; //Left thread
thread right_t; //Right thread
if (left < j)
left_t = thread(quickSort<T>, ref(arr), left, j);
if (i < right)
right_t = thread(quickSort<T>, ref(arr), i, right);
if (left < j)
left_t.join();
if (left < j)
right_t.join();
}
int main()
{
vector<int> table;
for (int i = 0; i < 100; i++)
{
table.push_back(rand() % 100);
}
cout << "Before" << endl;
for each(int val in table)
{
cout << val << endl;
}
quickSort(table, 0, 99);
cout << "After" << endl;
for each(int val in table)
{
cout << val << endl;
}
char temp = cin.get();
return 0;
}
Above program lags like mad hell and Spams "abort()" has been called.
Im thinking it has something to do with vectors and it Having threading issues
Iv seen the Question asked by Daniel Makardich, His Utilizes a Vector int While mine uses Vector T
You don't have any problem with quick sort, but with passing a templated function to a thread. There is no function quickSort. You need to explicitly give type, to instantiate the function template:
#include <thread>
#include <iostream>
template<typename T>
void f(T a) { std::cout << a << '\n'; }
int main () {
std::thread t;
int a;
std::string b("b");
t = std::thread(f, a); // Won't work
t = std::thread(f<int>, a);
t.join();
t = std::thread(f<decltype(b)>, b); // a bit fancier, more dynamic way
t.join();
return 0;
}
I suspect in your case this should do:
left_t = thread(quickSort<T>, ref(arr), left, j);
And similar for right_t. Also, you have mistake there trying to use operator()() instead of constructing an object. That is why the error is different.
Can't verify though, cause there's no minimal verifiable example =/
I don't know if it's possible to make compiler to use automatic type deduction for f passed as a param, if anyone knows that would probably make it a better answer.
Problem was with thread joins and what #luk32 said
Needed to convert the threads to pointers to threads.
thread* left_t = nullptr; //Left thread
thread* right_t = nullptr; //Right thread
if (left < j)
left_t = new thread(quickSort<T>, ref(arr), left, j);
if (i < right)
right_t = new thread(quickSort<T>, ref(arr), i, right);
if (left_t)
{
left_t->join();
delete left_t;
}
if (right_t)
{
right_t->join();
delete right_t;
}
Seems like if you create a default constructed thread object. But don't use it, it still wants to be joined. and if you do join it, it will complain.
I want read a paragraph by extracting one word at a time using Multithreading . Each thread should read exactly one word and when paragraph ends they should exit peacefully . I know threads shouldn't be used in this way as there is no advantage in that . But I want to do that so that I can check how threads can work sequentially if required . I tried but it looks like the program is reaching deadlock state and not giving any output at all . There are 11 words in the string and I am using 4 threads .
#include <iostream>
#include <mutex>
#include <sstream>
#include <thread>
#include <chrono>
#include <condition_variable>
using namespace std;
stringstream s("Japan US Canada UK France Germany China Russia Korea India Nepal");
int count = 0;
string word;
condition_variable cv;
mutex m;
int i = 0;
bool check_func(int i,int k)
{
return i == k;
}
void print(int k)
{
while(count < 11) // As there are 11 words
{
unique_lock<mutex> lk(m);
int z = k;
cv.wait(lk,[&]{return check_func(i,z);}); // Line 33
s >> word;
cout<<word<<" ";
i++;
cv.notify_all();
count++;
}
return;
}
int main()
{
thread threads[4];
for(int i = 0; i < 4; i++)
threads[i] = thread(print,i);
for(auto &t : threads)
t.join();
return 0;
}
You need to change this code:
while(count < 11) // As there are 11 words
{
unique_lock<mutex> lk(m);
int z = k;
cv.wait(lk,[&]{return check_func(i,z);}); // Line 33
s >> word;
cout<<word<<" ";
i++;
cv.notify_all();
count++;
}
To this:
int z = k;
while(z < 11) // As there are 11 words
{
unique_lock<mutex> lk(m);
int z = k;
cv.wait(lk,[&]{return check_func(i,z);}); // Line 33
s >> word;
cout<<word<<" ";
i++;
z+=4;
cv.notify_all();
count++;
}
Three things changed in the above: the declaration of z is moved outside of the loop, the condition in the while changed to check z instead of count, and the line z+=4 added. You need to increment z by 4 each time if you want each of your threads to move onto the next word. Also, you need to check z not count because otherwise some of the threads will overshoot and the last word will be printed multiple times (consider the thread that reads the ninth word: if checking on count instead of z it continues on to the next iteration of the loop even though there will be nothing further for it to read).
I am working on the Vigenere exercise from Harvard's CS50 (in case you noticed I'm using string and not str).
My program gives me a Floating Point Exception error when I use "a" in the keyword.
It actually gives me that error
when I use "a" by itself, and
when I use "a" within a bigger word it just gives me wrong output.
For any other kind of keyword, the program works perfectly fine.
I've run a million tests. Why is it doing this? I can't see where I'm dividing or % by 0. The length of the keyword is always at least 1. It is probably going to be some super simple mistake, but I've been at this for about 10 hours and I can barely remember my name.
#include <stdio.h>
#include <cs50.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
int main (int argc, string argv[])
{
//Error message if argc is not 2 and argv[1] is not alphabetical
if (argc != 2)
{
printf("Insert './vigenere' followed by an all alphabetical key\n");
return 1;
}
else if (argv[1])
{
for (int i = 0, n = strlen(argv[1]); i < n; i++)
{
if (isalpha((argv[1])[i]) == false)
{
printf("Insert './vigenere' followed by an all alphabetical key\n");
return 1;
}
}
//Store keyword in variable
string keyword = argv[1];
//Convert all capital chars in keyword to lowercase values, then converts them to alphabetical corresponding number
for (int i = 0, n = strlen(keyword); i < n; i++)
{
if (isupper(keyword[i])) {
keyword[i] += 32;
}
keyword[i] -= 97;
}
//Ask for users message
string message = GetString();
int counter = 0;
int keywordLength = strlen(keyword);
//Iterate through each of the message's chars
for (int i = 0, n = strlen(message); i < n; i++)
{
//Check if ith char is a letter
if (isalpha(message[i])) {
int index = counter % keywordLength;
if (isupper(message[i])) {
char letter = (((message[i] - 65) + (keyword[index])) % 26) + 65;
printf("%c", letter);
counter++;
} else if (islower(message[i])) {
char letter = (((message[i] - 97) + (keyword[index])) % 26) + 97;
printf("%c", letter);
counter++;
}
} else {
//Prints non alphabetic characters
printf("%c", message[i]);
}
}
printf("\n");
return 0;
}
}
This behavior is caused by the line keyword[i] -= 97;, there you make every 'a' in the key stream a zero. Later you use strlen() on the transformed key. So when the key starts with an 'a', keywordLength therefor is set to zero, and the modulo keywordLength operation get into a division by zero. You can fix this by calculating the keyword length before the key transformation.
Here is my problem with a pthread code. When I run the following commands:
./run 1
./run 2
./run 4
the first two commands (one thread and two threads) generate the same output. However with 4 threads (third command), I see different outputs.
Now when I run the following commands
valgrind --tool=helgrind ./run 1
valgrind --tool=helgrind ./run 2
valgrind --tool=helgrind ./run 4
They generate the same outputs. The output values are correct though.
How can I investigate further?
The code looks like
int main(int argc,char *argv[])
{
// Barrier initialization
if(pthread_barrier_init(&barr, NULL, threads)) {
printf("Could not create a barrier\n");
return -1;
}
int t;
for(t = 0; t < threads; ++t) {
printf("In main: creating thread %ld\n", t);
if(pthread_create(&td[t], NULL, &foo, (void*)t)) {
printf("Could not create thread %d\n", t);
return -1;
}
}
...
}
void * foo(void *threadid)
{
long tid = (long)threadid;
for ( i = (tid*n/threads)+1; i <= (tid+1)*n/threads; i++ ) {
printf( "Thread %d, i=%d\n", tid, i );
for(largest = i, j = i+1; j <= n; j++) {
if(abs( a[j][i] ) > abs( a[largest][i] ))
largest = j;
}
for(k = i; k <= n+1; k++)
SWAP_DOUBLE( a[largest][k], a[i][k]);
for( j = i+1; j <= n; j++) {
for( k = n+1; k >= i; k--)
a[j][k] = a[j][k]-a[i][k]*a[j][i]/a[i][i];
}
}
int rc = pthread_barrier_wait(&barr);
if(rc != 0 && rc != PTHREAD_BARRIER_SERIAL_THREAD) {
printf("Could not wait on barrier\n");
exit(-1);
}
printf("after barrier\n");
...
}
The main loop (which iterate over i in foo()) is divided by the number of threads. assume all variables are defined properly since as I said there is no problem with 1 and 2 threads.
I'm not entirely sure what's going on, since you haven't given a complete compilable program to experiment with, but it's clear that each of the threads is reading/writing from sections of a that it aren't assigned to it, so you have race conditions all over the place. You are swapping sections of a so I'm not sure you can parallelize this algorithm as it stands.