| PSERIALIZE(9) | Kernel Developer's Manual | PSERIALIZE(9) |
pserialize —
#include <sys/pserialize.h>
pserialize_t
pserialize_create(void);
void
pserialize_destroy(pserialize_t
psz);
int
pserialize_read_enter(void);
void
pserialize_read_exit(int
s);
void
pserialize_perform(pserialize_t
psz);
IPL_SOFTCLOCK.
pserialize_create()pserialize_destroy()pserialize_read_enter()pserialize_read_exit()pserialize_perform()
struct frotz {
...
struct frotz *f_next;
};
static struct {
kmutex_t lock;
pserialize_t psz;
struct frotz *first;
} frobbotzim __cacheline_aligned;
Create a frotz and publish it, as a writer:
struct frotz *f = pool_get(&frotz_pool, PR_WAITOK); /* Initialize f. */ ... mutex_enter(&frobbotzim.lock); f->f_next = frobbotzim.first; /* * Publish the contents of f->f_next before we publish the * pointer to f in frobbotzim.first. */ membar_producer(); frobbotzim.first = f; mutex_exit(&frobbotzim.lock);
Find a frotz, as a reader:
struct frotz *f;
int error = ENOENT;
int s;
s = pserialize_read_enter();
for (f = frobbotzim.first; f != NULL; f = f->f_next) {
/* Fetch f before we fetch anything f points to. */
membar_datadep_consumer();
if (f->f_... == key) {
/*
* Grab whatever part of the frotz we need.
* Note that we can't use the frotz after
* pserialize_read_exit, without a stronger
* kind of reference, say a reference count
* managed by atomic_ops(3).
*/
*resultp = f->f_...;
error = 0;
break;
}
}
pserialize_read_exit(s);
return error;
Remove a frotz, as a writer, and free it once there are no more readers:
struct frotz **fp, *f;
mutex_enter(&frobbotzim.lock);
for (fp = &frobbotzim.first; (f = *fp) != NULL; fp = &f->f_next) {
if (f->f_... == key) {
/*
* Unhook it from the list. Readers may still
* be traversing the list at this point, so
* the next pointer must remain valid and
* memory must remain allocated.
*/
*fp = f->f_next;
break;
}
}
/*
* Wait for all existing readers to complete. New readers will
* not see f because the list no longer points to it.
*/
pserialize_perform(frobbotzim.psz);
/* Now nobody else can be touching f, so it is safe to free. */
mutex_exit(&frobbotzim.lock);
if (f != NULL)
pool_put(&frotz_pool, f);
pserialize is implemented within the file
sys/kern/subr_pserialize.c.
Hennessy, et al., Passive serialization in a multitasking environment, US Patent and Trademark Office, US Patent 4809168, February 28, 1989.
| January 26, 2016 | NetBSD 9.1 |