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PPSi
Commit d39a15b9 authored by Adam Wujek's avatar Adam Wujek 💬
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arch-wrs: update shmem.c to version with WRS_SHM_LOCKED 

needed to implement shmem locking for ppsi
Signed-off-by: Adam Wujek's avatarAdam Wujek <adam.wujek@cern.ch>
parent e9f4a1f5
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Showing with 35 additions and 9 deletions
arch-wrs/shmem.c
View file @ d39a15b9
......@@ -11,13 +11,14 @@
#include <sys/mman.h>
#include <libwr/shmem.h>
#define SHM_LOCK_TIMEOUT 2
/* Get wrs shared memory */
/* return NULL and set errno on error */
void *wrs_shm_get(enum wrs_shm_name name_id, char *name, unsigned long flags)
{
struct wrs_shm_head *head;
struct stat stbuf;
struct timespec tv1, tv2;
void *map;
char fname[64];
int write_access = flags & WRS_SHM_WRITE;
......@@ -46,11 +47,32 @@ void *wrs_shm_get(enum wrs_shm_name name_id, char *name, unsigned long flags)
MAP_SHARED, fd, 0);
if (map == MAP_FAILED)
return NULL; /* keep errno */
if (!write_access)
return map;
/* Init the fields */
head = map;
if (!write_access) {
/* This is a reader: if locked, wait for a writer */
if (!(flags & WRS_SHM_LOCKED))
return map;
clock_gettime(CLOCK_MONOTONIC, &tv1);
while (1) {
/* Releasing does not mean initial data is in place! */
/* Read data with wrs_shm_seqbegin and
wrs_shm_seqend! */
if (head->pid && kill(head->pid, 0) == 0)
return map;
usleep(10 * 1000);
clock_gettime(CLOCK_MONOTONIC, &tv2);
if (tv2.tv_sec - tv1.tv_sec < SHM_LOCK_TIMEOUT)
continue;
errno = ETIMEDOUT;
return NULL;
}
}
/* Writer: init the fields */
if (head->pid && kill(head->pid, 0) == 0) {
munmap(map, WRS_SHM_MAX_SIZE);
errno = EBUSY;
......@@ -64,10 +86,14 @@ void *wrs_shm_get(enum wrs_shm_name name_id, char *name, unsigned long flags)
head->stamp = 0;
head->data_off = sizeof(*head);
head->data_size = 0;
head->pid = getpid();
if (flags & WRS_SHM_LOCKED)
head->sequence = 1; /* a sort of lock */
else
head->sequence = 0;
head->pid = getpid(); /* getpid() is a memory barrier, too */
head->pidsequence++;
/* version and size are up to the user (or to allocation) */
head->sequence = 0; /* a sort of unlock */
return map;
}
......@@ -119,12 +145,12 @@ void *wrs_shm_follow(void *headptr, void *ptr)
}
/* Before and after writing a chunk of data, act on sequence and stamp */
void wrs_shm_write(void *headptr, int begin)
void wrs_shm_write(void *headptr, int flags)
{
struct wrs_shm_head *head = headptr;
struct timespec tv;
if (!begin) {
if (flags == WRS_SHM_WRITE_END) {
/* At end-of-writing update the timestamp too */
clock_gettime(CLOCK_MONOTONIC, &tv);
head->stamp = tv.tv_sec;
......
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