2 wait for a tdb chain lock
4 Copyright (C) Andrew Tridgell 2006
6 This program is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 3 of the License, or
9 (at your option) any later version.
11 This program is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program; if not, see <http://www.gnu.org/licenses/>.
21 #include "system/filesys.h"
22 #include "system/wait.h"
24 #include "lib/tdb/include/tdb.h"
25 #include "lib/util/dlinklist.h"
26 #include "../include/ctdb_private.h"
29 struct lockwait_handle {
30 struct lockwait_handle *next, *prev;
31 struct ctdb_context *ctdb;
32 struct ctdb_db_context *ctdb_db;
37 void (*callback)(void *);
39 struct timeval start_time;
42 /* If we managed to obtain a lock, find any overflow records which wanted the
43 * same one and do all the callbacks at once. */
44 static void do_overflow(struct ctdb_db_context *ctdb_db,
47 struct lockwait_handle *i, *next;
48 TALLOC_CTX *tmp_ctx = talloc_new(ctdb_db);
50 for (i = ctdb_db->lockwait_overflow; i; i = next) {
51 /* Careful: destructor removes it from list! */
53 if (key.dsize == i->key.dsize
54 && memcmp(key.dptr, i->key.dptr, key.dsize) == 0) {
55 /* Callback might free them, so reparent. */
56 talloc_steal(tmp_ctx, i);
57 i->callback(i->private_data);
61 /* This will free them if callback didn't. */
64 /* Remove one from the overflow queue if there is one. */
65 if (ctdb_db->lockwait_overflow) {
66 i = ctdb_db->lockwait_overflow;
67 ctdb_lockwait(ctdb_db, i->key, i->callback, i->private_data);
72 static int lockwait_destructor(struct lockwait_handle *h)
74 CTDB_DECREMENT_STAT(h->ctdb, pending_lockwait_calls);
75 kill(h->child, SIGKILL);
76 h->ctdb_db->pending_requests--;
77 DLIST_REMOVE(h->ctdb_db->lockwait_active, h);
81 static void lockwait_handler(struct event_context *ev, struct fd_event *fde,
82 uint16_t flags, void *private_data)
84 struct lockwait_handle *h = talloc_get_type(private_data,
85 struct lockwait_handle);
86 void (*callback)(void *) = h->callback;
87 void *p = h->private_data;
88 TDB_DATA key = h->key;
89 struct tdb_context *tdb = h->ctdb_db->ltdb->tdb;
90 TALLOC_CTX *tmp_ctx = talloc_new(ev);
92 key.dptr = talloc_memdup(tmp_ctx, key.dptr, key.dsize);
93 h->ctdb_db->pending_requests--;
95 CTDB_UPDATE_LATENCY(h->ctdb, h->ctdb_db, "lockwait", lockwait_latency, h->start_time);
97 /* the handle needs to go away when the context is gone - when
98 the handle goes away this implicitly closes the pipe, which
99 kills the child holding the lock */
100 talloc_steal(tmp_ctx, h);
102 if (h->ctdb->flags & CTDB_FLAG_TORTURE) {
103 if (tdb_chainlock_nonblock(tdb, key) == 0) {
104 ctdb_fatal(h->ctdb, "got chain lock while lockwait child active");
108 tdb_chainlock_mark(tdb, key);
110 if (h->ctdb_db->lockwait_overflow) {
111 do_overflow(h->ctdb_db, key);
113 tdb_chainlock_unmark(tdb, key);
115 talloc_free(tmp_ctx);
119 static int overflow_lockwait_destructor(struct lockwait_handle *h)
121 CTDB_DECREMENT_STAT(h->ctdb, pending_lockwait_calls);
122 DLIST_REMOVE(h->ctdb_db->lockwait_overflow, h);
127 setup a non-blocking chainlock on a tdb record. If this function
128 returns NULL then it could not get the chainlock. Otherwise it
129 returns a opaque handle, and will call callback() once it has
130 managed to get the chainlock. You can cancel it by using talloc_free
131 on the returned handle.
133 It is the callers responsibility to unlock the chainlock once
136 struct lockwait_handle *ctdb_lockwait(struct ctdb_db_context *ctdb_db,
138 void (*callback)(void *private_data),
141 struct lockwait_handle *result, *i;
143 pid_t parent = getpid();
145 CTDB_INCREMENT_STAT(ctdb_db->ctdb, lockwait_calls);
146 CTDB_INCREMENT_STAT(ctdb_db->ctdb, pending_lockwait_calls);
148 if (!(result = talloc_zero(private_data, struct lockwait_handle))) {
149 CTDB_DECREMENT_STAT(ctdb_db->ctdb, pending_lockwait_calls);
153 result->callback = callback;
154 result->private_data = private_data;
155 result->ctdb = ctdb_db->ctdb;
156 result->ctdb_db = ctdb_db;
159 /* If we already have a lockwait child for this request, then put this
160 request on the overflow queue straight away
162 for (i = ctdb_db->lockwait_active; i; i = i->next) {
163 if (key.dsize == i->key.dsize
164 && memcmp(key.dptr, i->key.dptr, key.dsize) == 0) {
165 DLIST_ADD_END(ctdb_db->lockwait_overflow, result, NULL);
166 talloc_set_destructor(result, overflow_lockwait_destructor);
171 /* Don't fire off too many children at once! */
172 if (ctdb_db->pending_requests > 200) {
173 DLIST_ADD_END(ctdb_db->lockwait_overflow, result, NULL);
174 talloc_set_destructor(result, overflow_lockwait_destructor);
175 DEBUG(DEBUG_DEBUG, (__location__ " Created overflow for %s\n",
180 ret = pipe(result->fd);
184 CTDB_DECREMENT_STAT(ctdb_db->ctdb, pending_lockwait_calls);
188 result->child = ctdb_fork(ctdb_db->ctdb);
190 if (result->child == (pid_t)-1) {
191 close(result->fd[0]);
192 close(result->fd[1]);
194 CTDB_DECREMENT_STAT(ctdb_db->ctdb, pending_lockwait_calls);
198 if (result->child == 0) {
200 close(result->fd[0]);
201 debug_extra = talloc_asprintf(NULL, "chainlock-%s:", ctdb_db->db_name);
202 tdb_chainlock(ctdb_db->ltdb->tdb, key);
203 write(result->fd[1], &c, 1);
204 /* make sure we die when our parent dies */
205 while (kill(parent, 0) == 0 || errno != ESRCH) {
211 close(result->fd[1]);
212 set_close_on_exec(result->fd[0]);
214 /* This is an active lockwait child process */
215 DLIST_ADD_END(ctdb_db->lockwait_active, result, NULL);
217 DEBUG(DEBUG_DEBUG, (__location__ " Created PIPE FD:%d to child lockwait process\n", result->fd[0]));
219 ctdb_db->pending_requests++;
220 talloc_set_destructor(result, lockwait_destructor);
222 result->fde = event_add_fd(ctdb_db->ctdb->ev, result, result->fd[0],
223 EVENT_FD_READ, lockwait_handler,
225 if (result->fde == NULL) {
227 CTDB_DECREMENT_STAT(ctdb_db->ctdb, pending_lockwait_calls);
230 tevent_fd_set_auto_close(result->fde);
232 result->start_time = timeval_current();