问题
I'm working on the sleeping barber problem (using FIFO queue and shared memory), and I have a problem. I try to run this program just to see what is shown, however, I get segmentation fault every time. In the code I check, if semaphores are created successfully, if shared memory is created properly, but the program crashing must come from different place, which I cannot seem to find. I also tried to use Valgrind but what I got is:
Valgrind for the newer version of code: However, when I try to run the code I still get segfault
==187== Memcheck, a memory error detector
==187== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==187== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==187== Command: ./barber
==187==
Error while executing program, invalid amount of arguments==187==
==187== HEAP SUMMARY:
==187== in use at exit: 0 bytes in 0 blocks
==187== total heap usage: 1 allocs, 1 frees, 1,024 bytes allocated
==187==
==187== All heap blocks were freed -- no leaks are possible
==187==
==187== For lists of detected and suppressed errors, rerun with: -s
==187== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
==124== Memcheck, a memory error detector
==124== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==124== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==124== Command: ./barber
==124==
==124== Invalid read of size 1
==124== at 0x1094DD: main (in /mnt/c/users/Czaro/ubuntu/lab6posix/barber)
==124== Address 0x2 is not stack'd, malloc'd or (recently) free'd
==124==
==124==
==124== Process terminating with default action of signal 11 (SIGSEGV)
==124== Access not within mapped region at address 0x2
==124== at 0x1094DD: main (in /mnt/c/users/Czaro/ubuntu/lab6posix/barber)
==124== If you believe this happened as a result of a stack
==124== overflow in your program's main thread (unlikely but
==124== possible), you can try to increase the size of the
==124== main thread stack using the --main-stacksize= flag.
==124== The main thread stack size used in this run was 8388608.
glut==124==
==124== HEAP SUMMARY:
==124== in use at exit: 125 bytes in 4 blocks
==124== total heap usage: 5 allocs, 1 frees, 1,149 bytes allocated
==124==
==124== LEAK SUMMARY:
==124== definitely lost: 0 bytes in 0 blocks
==124== indirectly lost: 0 bytes in 0 blocks
==124== possibly lost: 0 bytes in 0 blocks
==124== still reachable: 125 bytes in 4 blocks
==124== suppressed: 0 bytes in 0 blocks
==124== Reachable blocks (those to which a pointer was found) are not shown.
==124== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==124==
==124== For lists of detected and suppressed errors, rerun with: -s
==124== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
Segmentation fault
I'd greatly appreciate every kind of help! The code for barber (newer version, with changes given by @AndrewHenle looks like this:
#include <stdio.h>
#include <stdlib.h>
#include <semaphore.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "functions.h"
#include <sys/mman.h>
#include <unistd.h>
int main(char* argv[], int argc)
{
if(argc < 2){
printf("Error while executing program, invalid amount of arguments");
return 0;
}
sem_t *barber;
sem_t *queue;
int seats;
int sharedmem, waitRoomSize;
struct Queue waitroom;
barber = sem_open("Barber", O_CREAT | O_RDWR, 0666, 1);
if((barber == SEM_FAILED)){
printf("Error while creating semaphore for barber");
exit(1);
}
queue = sem_open("Queue", O_CREAT | O_RDWR, 0666, 1);
if((queue == SEM_FAILED)) {
printf("Error while creating semaphore for queue");
exit(1);
}
seats = atoi(argv[1]);
void *space;
queueinit(waitroom, seats);
sharedmem = shm_open("Queue", O_RDWR, 0666);
if(sharedmem==-1){
printf("Error while getting shared memory");
exit(1);
}
waitRoomSize = ftruncate(sharedmem, sizeof(waitroom));
if((waitRoomSize ==-1)){
printf("Error while getting size");
exit(1);
}
space = mmap(NULL, sizeof(struct Queue), PROT_READ | PROT_WRITE, MAP_SHARED, sharedmem, 0);
if((space == MAP_FAILED)){
printf("B³¹d podczas mapowania pamiêci");
exit(1);
}
while(1)
{
printf("Starting work...");
sem_wait(queue);
sem_post(queue);
if(isEmpty(waitroom)) {
sem_wait(barber);
printf("Falling asleep \n");
sem_post(barber);
printf("Waking up \n");
}
sem_wait(queue);
sem_post(queue);
int id = get(waitroom);
printf("Customer: %d, please sit on the chair", id);
printf("I start making haircut: %d", id);
sleep(2);
printf("Finished making haircut for: %d", id);
}
sem_close(barber);
sem_unlink("Barber");
sem_close(queue);
sem_unlink("Queue");
}
Previous version:
#include <stdio.h>
#include <stdlib.h>
#include <semaphore.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "functions.h"
#include <sys/mman.h>
#include <unistd.h>
int main(char* argv, int argc)
{
sem_t *barber;
sem_t *queue;
int seats;
int sharedmem, waitRoomSize;
struct Queue waitroom;
barber = sem_open("Barber", O_CREAT | O_RDWR, 0666, 1);
if((barber == SEM_FAILED)){
printf("Error while creating semaphore for barber");
exit(1);
}
queue = sem_open("Queue", O_CREAT | O_RDWR, 0666, 1);
if((queue == SEM_FAILED)) {
printf("Error while creating semaphore for queue");
exit(1);
}
seats = atoi(argv[1]);
void *space;
queueinit(waitroom, seats);
if((sharedmem = shm_open("Queue", O_RDWR, 0666)==-1)){
printf("Error while getting shared memory");
exit(1);
}
if((waitRoomSize = ftruncate(sharedmem, sizeof(waitroom))==-1)){
printf("Error while getting size");
exit(1);
}
if((space = mmap(NULL, sizeof(struct Queue), PROT_READ | PROT_WRITE, MAP_SHARED, sharedmem, 0) == MAP_FAILED)){
printf("Błąd podczas mapowania pamięci");
exit(1);
}
while(1)
{
printf("Starting work...");
sem_wait(queue);
sem_post(queue);
if(isEmpty(waitroom)) {
sem_wait(barber);
printf("Falling asleep \n");
sem_post(barber);
printf("Waking up \n");
}
sem_wait(queue);
sem_post(queue);
int id = get(waitroom);
printf("Customer: %d, please sit on the chair", id);
printf("I start making haircut: %d", id);
sleep(2);
printf("Finished making haircut for: %d", id);
}
sem_close(barber);
sem_unlink("Barber");
sem_close(queue);
sem_unlink("Queue");
}
The FIFO queue is implemented like this:
#ifndef FUNCTIONS_H_INCLUDED
#define FUNCTIONS_H_INCLUDED
#include <stdlib.h>
#include <unistd.h>
struct Queue{
int* elems;
int qsize;
int head;
int tail;
int capacity;
};
void queueinit(struct Queue q, int capacity)
{
q.elems = malloc(capacity*(sizeof(int)));
q.capacity = capacity;
q.head = 0;
q.qsize = 0;
q.tail = capacity-1;
}
int isFull(struct Queue q)
{
return (q.qsize == q.capacity);
}
int isEmpty(struct Queue q)
{
return (q.qsize == 0);
}
void push(struct Queue q, int val)
{
if(isFull(q)){
printf("Kolejka pe³na");
return;
}
q.tail = (q.tail +1) % q.capacity;
q.elems[q.tail] = val;
q.qsize = q.qsize +1;
printf("%d zajmuje miejsce w kolejce", val);
}
int get(struct Queue q)
{
if(isEmpty(q))
{
printf("kolejka pusta");
return -1;
}
int val = q.elems[q.head];
q.head = (q.head +1) % q.capacity;
q.qsize = q.qsize -1;
printf("%d opuszcza zak³ad", val);
}
#endif // FUNCTIONS_H_INCLUDED
来源：https://stackoverflow.com/questions/65601643/posix-semaphores-cannot-determine-what-causes-segmentation-fault