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xlock.c
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xlock.c
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#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <linux/futex.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <string.h>
#define _GNU_SOURCE
#include <sys/syscall.h>
#define futex(uaddr, op, val, timeout, uaddr2, val3) \
syscall(SYS_futex , uaddr, op, val, NULL, NULL, NULL)
#include "xlock.h"
#include "debug.h"
static void inline
print_error(char *name) {
printf("ERR:%s:%d %s errno %d\n",
__FUNCTION__,
__LINE__,
name,
errno);
}
#define MAP_SZ (4096)
xlock_t *
xlock_create_open(char *name, int create_flag) {
int fd;
xlock_t *x;
int *lock_ptr;
int do_init = 0;
x = malloc(sizeof(xlock_t));
if (!x) {
print_error("malloc:");
free(x);
return NULL;
}
strncpy(x->name, name, sizeof(x->name));
if (create_flag) {
if ((fd = open(name, O_RDWR, 0666)) > 0){
free(x);
return NULL;
}
if ((fd = open(name, O_CREAT|O_RDWR, 0666)) < 0){
free(x);
print_error("open:");
return NULL;
}
ftruncate(fd, MAP_SZ);
close(fd);
}
if ((fd = open(name, O_RDWR, 0666)) < 0){
free(x);
print_error("open:");
return NULL;
}
lock_ptr = mmap(NULL, MAP_SZ, PROT_READ|PROT_WRITE,
MAP_SHARED, fd, 0);
if (lock_ptr == MAP_FAILED) {
free(x);
print_error("mmap:");
return NULL;
}
x->fd = fd;
x->lock_ptr = lock_ptr;
if (create_flag)
*(x->lock_ptr) = 0;
return x;
}
xlock_t*
xlock_create(char *name) {
return xlock_create_open(name, 1);
}
xlock_t*
xlock_open(char *name) {
return xlock_create_open(name, 0);
}
int
xlock_close(xlock_t *x){
if (*x->lock_ptr) {
print_error("closing a locked-lock: ");
return -1;
}
close(x->fd);
free(x);
}
#define IS_LOCKED(x) (*((x)->lock_ptr))
#define LOCK(x) (*((x)->lock_ptr) = 1)
#define UNLOCK(x) (*((x)->lock_ptr) = 0)
#ifdef LOCK_DEBUG
static void inline
print_xlock_debug(xlock_t *x) {
printf("curr pid %d val %d lock_pid %d unlock_pid %d\n",
getpid(), *(x->lock_ptr), x->lock_pid, x->unlock_pid);
}
static void inline
pre_lock_debug (xlock_t *x) {
printf("%s:pid %d before lock %d\n", __FUNCTION__, getpid(), *(x->lock_ptr));
if (IS_LOCKED(x)|| (x->lock_pid != x->unlock_pid))
print_xlock_debug(x);
}
static void inline
post_lock_debug(xlock_t *x) {
printf("%s: pid %d lock = %d futex\n",
__FUNCTION__, getpid(), *(x->lock_ptr));
x->lock_pid = getpid();
}
static void inline
pre_unlock_debug(xlock_t *x) {
printf("%s: pid %d lock %d\n", __FUNCTION__, getpid(), *(x->lock_ptr));
if (!IS_LOCKED(x) ||(x->lock_pid != getpid())) {
print_error("futex already unlocked:");
print_xlock_debug(x);
}
}
static void inline
post_unlock_debug(xlock_t *x) {
printf("%s: pid %d lock %d\n", __FUNCTION__, getpid(), *(x->lock_ptr));
x->unlock_pid = getpid();
}
#else
static void inline
pre_lock_debug (xlock_t *x) {
}
static void inline
post_lock_debug(xlock_t *x) {
}
static void inline
pre_unlock_debug(xlock_t *x) {
}
static void inline
post_unlock_debug(xlock_t *x) {
}
static void inline
print_xlock_debug(xlock_t *x) {
}
#endif
int
raw_lock_it(xlock_t *x) {
int ret;
ret = __sync_bool_compare_and_swap(x->lock_ptr, 0, 1);
return ret;
}
int
raw_unlock_it(xlock_t *x) {
int ret;
ret = __sync_bool_compare_and_swap(x->lock_ptr, 1, 0);
return ret;
}
int
xlock_lock(xlock_t *x) {
int ret;
pre_lock_debug(x);
do {
if (raw_lock_it(x))
break;
ret = futex(x->lock_ptr, FUTEX_WAIT, 1, NULL, NULL, 0);
}while (1);
post_lock_debug(x);
return ret;
}
int
xlock_unlock(xlock_t *x) {
pre_unlock_debug(x);
do {
if (raw_unlock_it(x)) {
futex(x->lock_ptr, FUTEX_WAKE, -1, NULL, NULL, 0);
break;
}
else {
print_xlock_debug(x);
}
}while(1);
post_unlock_debug(x);
return 0;
}
void xlock_destroy(xlock_t *x) {
close(x->fd);
unlink(x->name);
free(x);
}