[英]Segmentation Fault when trying to lock a shared memory mutex
共享內存互斥鎖上的分段錯誤。 我分別有一個生產者進程和一個使用者進程,生產者初始化共享內存,共享內存互斥量並寫入數據。
使用者打開共享內存,嘗試鎖定並讀取數據。
沒有互斥量,使用者就可以讀取數據(數據將不一致,但是沒有段錯誤)
僅當使用者嘗試鎖定互斥鎖時才存在段錯誤。
更改標志,結果相同,檢查attr和互斥鎖init的返回值,它們都很好。
我有點迷茫,對共享內存的研究還很新。
指出的任何缺陷將非常有幫助。 謝謝!
堆:
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff79c0c8d in pthread_mutex_lock () from /lib64/libpthread.so.0
(gdb) bt
#0 0x00007ffff79c0c8d in pthread_mutex_lock () from /lib64/libpthread.so.0
#1 0x00000000004008ec in main (argc=1, argv=0x7fffffffde18 "\210\341\377\377\377\177") at cons.c:41
(gdb) p cons_ptr
$1 = (test_str_t *) 0x7ffff7ff7000
(gdb) p cons_ptr->data[0]
$2 = 873422052
(gdb) p cons_ptr->magic
$3 = 43981
(gdb) p cons_ptr->shm_lock
$4 = {__data = {__lock = 0, __count = 0, __owner = 0, __nusers = 0, __kind = 128, __spins = 0, __elision = 0, __list = {__prev = 0x0, __next = 0x0}},
__size = '\000' <repeats 16 times>, "\200", '\000' <repeats 22 times>, __align = 0}
(gdb)
// Header:
const char *pathname = "test_shm";
typedef struct test_str_{
uint64_t magic;
int data[1024];
pthread_mutex_t shm_lock;
uint64_t magic2;
}test_str_t;
// Producer:
#include "test_header.h"
#include <time.h>
test_str_t *ptr;
void init_mutex(pthread_mutex_t *mutex){
pthread_mutexattr_t attr;
pthread_mutexattr_init(&attr);
pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);
pthread_mutex_init(mutex, &attr);
pthread_mutexattr_destroy(&attr);
}
int main(int argc, char *argv[]) {
int fd, i = 0, num_int = 1024, rc = 0;
int size = num_int * sizeof(int);
fd = shm_open(pathname, O_CREAT|O_RDWR, 0666);
if(fd == -1) {
printf("\n shm_open failed \n");
exit(0);
}
rc = ftruncate(fd, sizeof(test_str_t));
ptr = (test_str_t *)mmap(NULL, sizeof(test_str_t),
PROT_WRITE | PROT_READ, MAP_SHARED, fd, 0);
if(ptr == MAP_FAILED) {
printf("\n mmap failed \n");
exit(0);
}
rc = init_mutex(&(ptr->shm_lock));
if(rc != 0) {
printf("Mutex Init failed: rc:[%d]\n", rc);
exit(0);
}
ptr->magic = 0xABCD;
ptr->magic2 = 0xEF12;
srand(time(0));
for(i = 0; i < 5; i++) {
pthread_mutex_lock(&(ptr->shm_lock));
ptr->data[i] = i;
pthread_mutex_unlock(&(ptr->shm_lock));
}
return 0;
}
// Consumer:
#include "test_header.h"
#include <time.h>
test_str_t *cons_ptr;
int main(int argc, char *argv[]) {
int fd, i = 0, num_int = 1024, rc = 0;
int try_lock = 0;
int size = num_int * sizeof(int);
fd = shm_open(pathname, O_RDONLY, 0666);
if(fd == -1) {
printf("\n shm_open failed \n");
exit(0);
}
cons_ptr = (test_str_t *)mmap(NULL, sizeof(test_str_t),
PROT_READ, MAP_SHARED, fd, 0);
if(cons_ptr == MAP_FAILED) {
printf("\n mmap failed \n");
exit(0);
}
if(cons_ptr == NULL) {
printf("\n NULL Ptr\n");
return 0;
}
printf("Magic: [0x%x] [0x%x]\n", cons_ptr->magic, cons_ptr->magic2);
//int try_lock = pthread_mutex_lock(&(cons_ptr->shm_lock)); // SEG FAULT
for(i = 0; i < 5; i++) {
printf("\nNumber:[%d]\n", cons_ptr->data[i]);
sleep(1);
}
//pthread_mutex_unlock(&(cons_ptr->shm_lock)); // SEG FAULT
return 0;
}
(1)一個問題在這里:ptr-> data = rand(); data是一個int *,並且您已將該指針替換為隨機地址。 您在幾個地方執行了此操作,但我看不到發生了什么,但這是我現在看到的最明顯的錯誤。
(2)我看到的第二件事是,在使用者中,您以只讀方式打開文件並將內存映射為只讀,但是pthread_mutex_lock和pthread_mutex_unlock必須能夠修改互斥鎖,這樣可能會引起一些麻煩。
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