I was told to write a program to make two processes which will synchronize with each other to print '00110011...'
I have the following code:
#include"headers.h"
int main(int argc, char* argv[]){
sem_t smid;
if(sem_init(&smid, 1, 1)<0){
perror("sem_init");
exit(EXIT_FAILURE);
}
int pid = fork();
if(pid == 0){
//child process
while(1){
if(sem_wait(&smid)<0){
perror("sem_wait");
exit(EXIT_FAILURE);
}
printf("00");
sleep(1);
if(sem_post(&smid)<0){
perror("sem post");
exit(EXIT_FAILURE);
}
}
}else{
while(1){
if(sem_wait(&smid)<0){
perror("sem_wait");
exit(EXIT_FAILURE);
}
printf("11");
sleep(1);
if(sem_post(&smid)<0){
perror("sem post");
exit(EXIT_FAILURE);
}
}
}
return 0;
}
header.s:
#include<stdlib.h>
#include<stdio.h>
#include<semaphore.h>
#include<unistd.h>
The above code results in a deadlock and I can't understand why.
P.S. I have noticed that the deadlock is removed when I remove both the sleep() function calls.
I need to understand where I am going wrong. Any help is appreciated. Thanks in advance.
Related
I'm trying to read memory usage(PSS, specifically) of a child process by reading its proc filesystem when the child process is about to be terminated.
Following this and this answers, I managed to hook SIGCHLD signal of child process and read some data from proc filesystem. I found it works well for most of the proc filesystem, but doesn't work for /proc/PID/maps and /proc/PID/smaps. It looks like both maps and smaps are already empty when SIGCHLD signal is emitted. If it is too late to read maps and smaps when SIGCHLD is emitted, what alternative approach could I have? Any hint would be appreciated. thanks.
The following is example code copied from the second answer I linked above.
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <pthread.h>
pthread_mutex_t mutex;
void sigchldhandler(int s) {
// signals to the main thread that child has exited
pthread_mutex_unlock(&mutex);
}
int main() {
// init and lock the mutex
pthread_mutex_init(&mutex, NULL);
pthread_mutex_lock(&mutex);
// install signal handler
signal(SIGCHLD, sigchldhandler);
pid_t child_pid = fork();
if (child_pid > 0) {
// parent
// wait for the signal
pthread_mutex_lock(&mutex);
char buffer[0x1000];
sprintf(buffer, "/proc/%d/io", child_pid);
FILE * fp = fopen(buffer, "r");
if (!fp) {
perror("fopen");
abort();
}
while (fgets(buffer, sizeof(buffer), fp)) {
printf("%s", buffer);
}
// clean up child
wait(0);
return 0;
} else if (child_pid < 0) {
perror("fork");
abort();
} else {
// child
char* args[] = { "cat", "test.txt" };
execv(args[0], args);
}
}
I want to use the pin to track the address of the first 256*256 instructions, but I don't know how to stop the pin after the number is reached. I know there is a method PIN_ExitProcess(), but make will cause an error after adding it. Is there any other way?
#include <stdio.h>
#include "pin.H"
FILE * trace;
VOID printip(VOID *ip) {
fprintf(trace, "%p\n", ip);
}
VOID Instruction(INS ins, VOID *v)
{
if(0x70000000>INS_Address(ins))
INS_InsertCall(ins, IPOINT_BEFORE, (AFUNPTR)printip, IARG_INST_PTR, IARG_END);
}
VOID Fini(INT32 code, VOID *v)
{
fprintf(trace, "#eof\n");
fclose(trace);
}
INT32 Usage()
{
PIN_ERROR("This Pintool prints the IPs of every instruction executed\n"
+ KNOB_BASE::StringKnobSummary() + "\n");
return -1;
}
int main(int argc, char * argv[])
{
trace = fopen("itrace.out", "w");
if (PIN_Init(argc, argv)) return Usage();
INS_AddInstrumentFunction(Instruction, 0);
PIN_AddFiniFunction(Fini, 0);
PIN_StartProgram();
return 0;
}
You have two options:
Simply count the number of traced instructions and stop fprintfing when you reach the threshold using an if statement.
Call PIN_Detach() when the instruction threshold is reached. See more here: https://software.intel.com/sites/landingpage/pintool/docs/97503/Pin/html/group__PIN__CONTROL.html#ga6277d16bf33ede39685a26a92fc3cbef
I want to create MPI communicators linking the process with rank 0 to every other process. Suppose n is the total number of processes. Then the process with rank 0 is supposed to have n-1 communicators while each of the other processes has one communicator. Is this possible, and, if it is, why can I not use the program below to achieve this?
Compiling the code below using the mpic++ compiler terminates without warnings and errors on my computer. But when I run the resulting program using 3 or more processes (mpiexec -n 3), it never terminates.
Likely I'm misunderstanding the concept of communicators in MPI. Maybe someone can help me understand why the program below gets stuck, and what is a better way to create those communicators? Thanks.
#include <iostream>
#include <vector>
#include <thread>
#include <chrono>
#include "mpi.h"
void FinalizeMPI();
void InitMPI(int argc, char** argv);
int main(int argc, char** argv) {
InitMPI(argc, argv);
int rank,comm_size;
MPI_Comm_rank(MPI_COMM_WORLD,&rank);
MPI_Comm_size(MPI_COMM_WORLD,&comm_size);
if(comm_size<2) {
FinalizeMPI();
return 0;
}
MPI_Group GroupAll;
MPI_Comm_group(MPI_COMM_WORLD, &GroupAll);
if(rank==0) {
std::vector<MPI_Group> myGroups(comm_size-1);
std::vector<MPI_Comm> myComms(comm_size-1);
for(int k=1;k<comm_size;++k) {
int ranks[2]{0, k};
MPI_Group_incl(GroupAll, 2, ranks, &myGroups[k-1]);
int err = MPI_Comm_create(MPI_COMM_WORLD, myGroups[k-1], &myComms[k-1]);
std::cout << "Error: " << err << std::endl;
}
} else {
MPI_Group myGroup;
MPI_Comm myComm;
int ranks[2]{0,rank};
MPI_Group_incl(GroupAll, 2, ranks, &myGroup);
int err = MPI_Comm_create(MPI_COMM_WORLD, myGroup, &myComm);
std::cout << "Error: " << err << std::endl;
}
std::cout << "Communicators created: " << rank << std::endl;
std::this_thread::sleep_for(std::chrono::milliseconds(1000));
FinalizeMPI();
return 0;
}
void FinalizeMPI() {
int flag;
MPI_Finalized(&flag);
if(!flag)
MPI_Finalize();
}
void InitMPI(int argc, char** argv) {
int flag;
MPI_Initialized(&flag);
if(!flag) {
int provided_Support;
MPI_Init_thread(&argc, &argv, MPI_THREAD_MULTIPLE, &provided_Support);
if(provided_Support!=MPI_THREAD_MULTIPLE) {
exit(0);
}
}
}
MPI_Comm_create is a collective operation on the initial communicator (MPI_COMM_WORLD) - you must call it on all processes.
The simplest way to fix the issue is to use MPI_Comm_create_group just the way you do it. It is similar to MPI_Comm_create except that it is collective over the group.
#include<stdio.h>
main()
{char *names[4];
int i,a;
printf("ënter the guests names\n");
for(i=0;i<=3;i++)
{
scanf("%s",names[i]);
}
char *yourname;
printf("\nenter your name ");
scanf("%c",yourname);
for(i=0;i<=3;i++)
{a=strcmp(names[i],yourname);
if(a==0)
printf("\nwelcome");
break;
}
if(a!=0)
printf("\naccess denied");
return 0;
}
this is a program to check your entry in a show. first we give permitted names & then it asks your name ,it compares your name with the names in the guest list.
i m getting runtime error, plz tell me the correction.i want to use pointers to string so plz suggest correction in the existing program
when i run this program in devc++ after entering first name it gives program.exe stopped working.
The code will be like this:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main()
{
char *names[4];
int i,a;
printf("ënter the guests names\n");
for(i=0;i<=3;i++) {
names[i] = (char*) malloc(100 * sizeof(char));
scanf("%s", names[i]);
}
char yourname[100];
printf("\nenter your name ");
scanf("%s",yourname);
for(i=0;i<=3;i++) {
a = strcmp(names[i], yourname);
if (a == 0) break;
}
if (a==0)
printf("\nwelcome");
else printf("\naccess denied");
for(i=0;i<=3;i++)
free(names[i]);
return 0;
}
Your code have to be formated so we can give you a better answer.
Now, use gets to take your input, verify the guest match with your name inside the for loop, stop the loop when a match is found.
#include<stdio.h>
#include<string.h>
int main()
{
char names[4][20];
int i = 0;
int a = 0;
printf("Enter guests names: \n");
for(i=0; i<3; i++)
{
gets(names[i]);
}
char yourname[20];
printf("\n Enter your name ");
gets(yourname);
printf("\n Verify access right:");
for(i=0; i<3; i++)
{
a=strcmp(names[i], yourname);
if(a==0)
{
printf("\n welcome");
break;
}
else
{
printf("\n access denied");
}
}
return 0;
}
Although this looks like a homework assignment.
I need to create three child processes, each of which reads a string from the command line arguments and writes the string to a single pipe. The parent would then read the strings from the pipe and display all three of them on the screen. I tried doing it for two processes to test and it is printing one of the strings twice as opposed to both of them.
#include <stdio.h>
#include <unistd.h>
int main (int argc, char *argv[]) {
char *character1 = argv[1];
char *character2 = argv[2];
char inbuf[100]; //creating an array with a max size of 100
int p[2]; // Pipe descriptor array
pid_t pid1; // defining pid1 of type pid_t
pid_t pid2; // defining pid2 of type pid_t
if (pipe(p) == -1) {
fprintf(stderr, "Pipe Failed"); // pipe fail
}
pid1 = fork(); // fork
if (pid1 < 0) {
fprintf(stderr, "Fork Failed"); // fork fail
}
else if (pid1 == 0){ // if child process 1
close(p[0]); // close the read end
write(p[1], character1, sizeof(&inbuf[0])); // write character 1 to the pipe
}
else { // if parent, create a second child process, child process 2
pid2 = fork();
if (pid2 < 0) {
fprintf(stderr, "Fork Failed"); // fork fail
}
if (pid2 = 0) { // if child process 2
close(p[0]); // close the read end
write(p[1], character2, sizeof(&inbuf[0])); // write character 2 to the pipe
}
else { // if parent process
close(p[1]); // close the write end
read(p[0], inbuf, sizeof(&inbuf[0])); // Read the pipe that both children write to
printf("%s\n", inbuf); // print
read(p[0], inbuf, sizeof(&inbuf[0])); // Read the pipe that both children write to
printf("%s\n", inbuf); // print
}
}
}
Your code doesn't keep looping until there's no more data to read. It does a single read. It also doesn't check the value returned by read(), but it should.
I've abstracted the fork() and write() (and error check) code into a function. This seems to work:
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
static void child(int fd, const char *string)
{
pid_t pid = fork();
int len = strlen(string);
if (pid < 0)
{
fprintf(stderr, "%.5d: failed to fork (%d: %s)\n",
(int)getpid(), errno, strerror(errno));
exit(1);
}
else if (pid > 0)
return;
else if (write(fd, string, len) != len)
{
fprintf(stderr, "%.5d: failed to write on pipe %d (%d: %s)\n",
(int)getpid(), fd, errno, strerror(errno));
exit(1);
}
else
exit(0);
}
int main (int argc, char *argv[])
{
char inbuf[100]; //creating an array with a max size of 100
int p[2]; // Pipe descriptor array
if (argc != 4)
{
fprintf(stderr, "Usage: %s str1 str2 str3\n", argv[0]);
return 1;
}
if (pipe(p) == -1)
{
fprintf(stderr, "Pipe Failed"); // pipe fail
return 1;
}
for (int i = 0; i < 3; i++)
child(p[1], argv[i+1]);
int nbytes;
close(p[1]); // close the write end
while ((nbytes = read(p[0], inbuf, sizeof(inbuf))) > 0)
printf("%.*s\n", nbytes, inbuf); // print
return 0;
}
I ran the command multiple times, each time using the command line:
./p3 'message 1' 'the second message' 'a third message for the third process'
On one run, the output was:
the second messagemessage 1
a third message for the third process
On another, I got:
the second messagemessage 1a third message for the third process
And on another, I got:
message 1
the second messagea third message for the third process
(This is on a MacBook Pro with Intel Core i7, running Mac OS X 10.8.3, and using GCC 4.7.1.)