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/*
wait for a tdb chain lock
Copyright (C) Andrew Tridgell 2006
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#include "includes.h"
#include "system/filesys.h"
#include "system/wait.h"
#include "db_wrap.h"
#include "lib/tdb/include/tdb.h"
#include "lib/util/dlinklist.h"
#include "../include/ctdb_private.h"
struct lockwait_handle {
struct lockwait_handle *next, *prev;
struct ctdb_context *ctdb;
struct ctdb_db_context *ctdb_db;
struct fd_event *fde;
int fd[2];
pid_t child;
void *private_data;
void (*callback)(void *);
TDB_DATA key;
struct timeval start_time;
};
/* If we managed to obtain a lock, find any overflow records which wanted the
* same one and do all the callbacks at once. */
static void do_overflow(struct ctdb_db_context *ctdb_db,
TDB_DATA key)
{
struct lockwait_handle *i, *next;
TALLOC_CTX *tmp_ctx = talloc_new(ctdb_db);
for (i = ctdb_db->lockwait_overflow; i; i = next) {
/* Careful: destructor removes it from list! */
next = i->next;
if (key.dsize == i->key.dsize
&& memcmp(key.dptr, i->key.dptr, key.dsize) == 0) {
/* Callback might free them, so reparent. */
talloc_steal(tmp_ctx, i);
i->callback(i->private_data);
}
}
/* This will free them if callback didn't. */
talloc_free(tmp_ctx);
/* Remove one from the overflow queue if there is one. */
if (ctdb_db->lockwait_overflow) {
i = ctdb_db->lockwait_overflow;
ctdb_lockwait(ctdb_db, i->key, i->callback, i->private_data);
talloc_free(i);
}
}
static int lockwait_destructor(struct lockwait_handle *h)
{
CTDB_DECREMENT_STAT(h->ctdb, pending_lockwait_calls);
kill(h->child, SIGKILL);
h->ctdb_db->pending_requests--;
DLIST_REMOVE(h->ctdb_db->lockwait_active, h);
return 0;
}
static void lockwait_handler(struct event_context *ev, struct fd_event *fde,
uint16_t flags, void *private_data)
{
struct lockwait_handle *h = talloc_get_type(private_data,
struct lockwait_handle);
void (*callback)(void *) = h->callback;
void *p = h->private_data;
TDB_DATA key = h->key;
struct tdb_context *tdb = h->ctdb_db->ltdb->tdb;
TALLOC_CTX *tmp_ctx = talloc_new(ev);
key.dptr = talloc_memdup(tmp_ctx, key.dptr, key.dsize);
h->ctdb_db->pending_requests--;
CTDB_UPDATE_LATENCY(h->ctdb, h->ctdb_db, "lockwait", lockwait_latency, h->start_time);
/* the handle needs to go away when the context is gone - when
the handle goes away this implicitly closes the pipe, which
kills the child holding the lock */
talloc_steal(tmp_ctx, h);
if (h->ctdb->flags & CTDB_FLAG_TORTURE) {
if (tdb_chainlock_nonblock(tdb, key) == 0) {
ctdb_fatal(h->ctdb, "got chain lock while lockwait child active");
}
}
tdb_chainlock_mark(tdb, key);
callback(p);
if (h->ctdb_db->lockwait_overflow) {
do_overflow(h->ctdb_db, key);
}
tdb_chainlock_unmark(tdb, key);
talloc_free(tmp_ctx);
}
static int overflow_lockwait_destructor(struct lockwait_handle *h)
{
CTDB_DECREMENT_STAT(h->ctdb, pending_lockwait_calls);
DLIST_REMOVE(h->ctdb_db->lockwait_overflow, h);
return 0;
}
/*
setup a non-blocking chainlock on a tdb record. If this function
returns NULL then it could not get the chainlock. Otherwise it
returns a opaque handle, and will call callback() once it has
managed to get the chainlock. You can cancel it by using talloc_free
on the returned handle.
It is the callers responsibility to unlock the chainlock once
acquired
*/
struct lockwait_handle *ctdb_lockwait(struct ctdb_db_context *ctdb_db,
TDB_DATA key,
void (*callback)(void *private_data),
void *private_data)
{
struct lockwait_handle *result, *i;
int ret;
pid_t parent = getpid();
CTDB_INCREMENT_STAT(ctdb_db->ctdb, lockwait_calls);
CTDB_INCREMENT_STAT(ctdb_db->ctdb, pending_lockwait_calls);
if (!(result = talloc_zero(private_data, struct lockwait_handle))) {
CTDB_DECREMENT_STAT(ctdb_db->ctdb, pending_lockwait_calls);
return NULL;
}
result->callback = callback;
result->private_data = private_data;
result->ctdb = ctdb_db->ctdb;
result->ctdb_db = ctdb_db;
result->key = key;
/* If we already have a lockwait child for this request, then put this
request on the overflow queue straight away
*/
for (i = ctdb_db->lockwait_active; i; i = i->next) {
if (key.dsize == i->key.dsize
&& memcmp(key.dptr, i->key.dptr, key.dsize) == 0) {
DLIST_ADD_END(ctdb_db->lockwait_overflow, result, NULL);
talloc_set_destructor(result, overflow_lockwait_destructor);
return result;
}
}
/* Don't fire off too many children at once! */
if (ctdb_db->pending_requests > 200) {
DLIST_ADD_END(ctdb_db->lockwait_overflow, result, NULL);
talloc_set_destructor(result, overflow_lockwait_destructor);
DEBUG(DEBUG_DEBUG, (__location__ " Created overflow for %s\n",
ctdb_db->db_name));
return result;
}
ret = pipe(result->fd);
if (ret != 0) {
talloc_free(result);
CTDB_DECREMENT_STAT(ctdb_db->ctdb, pending_lockwait_calls);
return NULL;
}
result->child = ctdb_fork(ctdb_db->ctdb);
if (result->child == (pid_t)-1) {
close(result->fd[0]);
close(result->fd[1]);
talloc_free(result);
CTDB_DECREMENT_STAT(ctdb_db->ctdb, pending_lockwait_calls);
return NULL;
}
if (result->child == 0) {
char c = 0;
close(result->fd[0]);
debug_extra = talloc_asprintf(NULL, "chainlock-%s:", ctdb_db->db_name);
tdb_chainlock(ctdb_db->ltdb->tdb, key);
write(result->fd[1], &c, 1);
/* make sure we die when our parent dies */
while (kill(parent, 0) == 0 || errno != ESRCH) {
sleep(5);
}
_exit(0);
}
close(result->fd[1]);
set_close_on_exec(result->fd[0]);
/* This is an active lockwait child process */
DLIST_ADD_END(ctdb_db->lockwait_active, result, NULL);
DEBUG(DEBUG_DEBUG, (__location__ " Created PIPE FD:%d to child lockwait process\n", result->fd[0]));
ctdb_db->pending_requests++;
talloc_set_destructor(result, lockwait_destructor);
result->fde = event_add_fd(ctdb_db->ctdb->ev, result, result->fd[0],
EVENT_FD_READ, lockwait_handler,
(void *)result);
if (result->fde == NULL) {
talloc_free(result);
CTDB_DECREMENT_STAT(ctdb_db->ctdb, pending_lockwait_calls);
return NULL;
}
tevent_fd_set_auto_close(result->fde);
result->start_time = timeval_current();
return result;
}
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