2 Bacula® - The Network Backup Solution
4 Copyright (C) 2000-2008 Free Software Foundation Europe e.V.
6 The main author of Bacula is Kern Sibbald, with contributions from
7 many others, a complete list can be found in the file AUTHORS.
8 This program is Free Software; you can redistribute it and/or
9 modify it under the terms of version two of the GNU General Public
10 License as published by the Free Software Foundation and included
13 This program is distributed in the hope that it will be useful, but
14 WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 General Public License for more details.
18 You should have received a copy of the GNU General Public License
19 along with this program; if not, write to the Free Software
20 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
23 Bacula® is a registered trademark of Kern Sibbald.
24 The licensor of Bacula is the Free Software Foundation Europe
25 (FSFE), Fiduciary Program, Sumatrastrasse 25, 8006 Zürich,
26 Switzerland, email:ftf@fsfeurope.org.
29 * Collection of Bacula Storage daemon locking software
31 * Kern Sibbald, 2000-2007. June 2007
36 #include "bacula.h" /* pull in global headers */
37 #include "stored.h" /* pull in Storage Deamon headers */
42 const int dbglvl = 500;
48 * The Storage daemon has three locking concepts that must be
51 * 1. dblock blocking the device, which means that the device
52 * is "marked" in use. When setting and removing the
53 block, the device is locked, but after dblock is
54 called the device is unlocked.
55 * 2. dlock() simple mutex that locks the device structure. A dlock
56 * can be acquired while a device is blocked if it is not
58 * 3. r_dlock "recursive" dlock, when means that a dlock (mutex)
59 * will be acquired on the device if it is not blocked
60 * by some other thread. If the device was blocked by
61 * the current thread, it will acquire the lock.
62 * If some other thread has set a block on the device,
63 * this call will wait until the device is unblocked.
65 * A lock is normally set when modifying the device structure.
66 * A r_lock is normally acquired when you want to block the device
67 * i.e. it will wait until the device is not blocked.
68 * A block is normally set during long operations like writing to
70 * If you are writing the device, you will normally block and
72 * A lock cannot be violated. No other thread can touch the
73 * device while a lock is set.
74 * When a block is set, every thread accept the thread that set
75 * the block will block if r_dlock is called.
76 * A device can be blocked for multiple reasons, labeling, writing,
77 * acquiring (opening) the device, waiting for the operator, unmounted,
79 * Under certain conditions the block that is set on a device can be
80 * stolen and the device can be used by another thread. For example,
81 * a device is blocked because it is waiting for the operator to
82 * mount a tape. The operator can then unmount the device, and label
83 * a tape, re-mount it, give back the block, and the job will continue.
88 * DEVICE::dlock() does P(m_mutex) (in dev.h)
89 * DEVICE::dunlock() does V(m_mutex)
91 * DEVICE::r_dlock() allows locking the device when this thread
92 already has the device blocked.
94 * if blocked and not same thread that locked
96 * leaves device locked
98 * DEVICE::r_dunlock() unlocks but does not unblock
101 * DEVICE::dblock(why) does
102 * r_dlock(); (recursive device lock)
103 * block_device(this, why)
106 * DEVICE::dunblock does
111 * block_device() does (must be locked and not blocked at entry)
115 * unblock_device() does (must be blocked at entry)
118 * set unblocked status
121 * pthread_cond_broadcast
123 * steal_device_lock() does (must be locked and blocked at entry)
125 * set new blocked status
129 * give_back_device_lock() does (must be blocked but not locked)
131 * reset blocked status
132 * save previous blocked
135 * pthread_cond_broadcast
140 void DEVICE::dblock(int why)
142 r_dlock(); /* need recursive lock to block */
143 block_device(this, why);
147 void DEVICE::dunblock(bool locked)
152 unblock_device(this);
158 void DCR::_dlock(const char *file, int line)
160 dev->_dlock(file, line);
163 void DCR::_dunlock(const char *file, int line)
165 m_dev_locked = false;
166 dev->_dunlock(file, line);
170 void DEVICE::_dlock(const char *file, int line)
172 Dmsg3(sd_dbglvl, "dlock from %s:%d precnt=%d\n", file, line, m_count);
173 /* Note, this *really* should be protected by a mutex, but
174 * since it is only debug code we don't worry too much.
176 if (m_count > 0 && pthread_equal(m_pid, pthread_self())) {
177 Dmsg4(sd_dbglvl, "Possible DEADLOCK!! lock held by JobId=%u from %s:%d m_count=%d\n",
178 get_jobid_from_tid(m_pid),
179 file, line, m_count);
182 m_pid = pthread_self();
186 void DEVICE::_dunlock(const char *file, int line)
189 Dmsg3(sd_dbglvl+1, "dunlock from %s:%d postcnt=%d\n", file, line, m_count);
193 void DEVICE::_r_dunlock(const char *file, int line)
195 this->_dunlock(file, line);
202 * This is a recursive lock that checks if the device is blocked.
204 * When blocked is set, all threads EXCEPT thread with id no_wait_id
205 * must wait. The no_wait_id thread is out obtaining a new volume
206 * and preparing the label.
209 void DEVICE::_r_dlock(const char *file, int line)
211 Dmsg3(sd_dbglvl+1, "r_dlock blked=%s from %s:%d\n", this->print_blocked(),
214 void DEVICE::r_dlock()
218 P(m_mutex); /* this->dlock(); */
219 m_count++; /* this->dlock() */
220 if (this->blocked() && !pthread_equal(this->no_wait_id, pthread_self())) {
221 this->num_waiting++; /* indicate that I am waiting */
222 while (this->blocked()) {
224 /* thread id on Win32 may be a struct */
225 Dmsg3(sd_dbglvl, "r_dlock blked=%s no_wait=%p me=%p\n", this->print_blocked(),
226 this->no_wait_id, pthread_self());
228 if ((stat = pthread_cond_wait(&this->wait, &m_mutex)) != 0) {
231 Emsg1(M_ABORT, 0, _("pthread_cond_wait failure. ERR=%s\n"),
235 this->num_waiting--; /* no longer waiting */
240 * Block all other threads from using the device
241 * Device must already be locked. After this call,
242 * the device is blocked to any thread calling dev->r_lock(),
243 * but the device is not locked (i.e. no P on device). Also,
244 * the current thread can do slip through the dev->r_lock()
245 * calls without blocking.
247 void _block_device(const char *file, int line, DEVICE *dev, int state)
249 ASSERT(dev->blocked() == BST_NOT_BLOCKED);
250 dev->set_blocked(state); /* make other threads wait */
251 dev->no_wait_id = pthread_self(); /* allow us to continue */
252 Dmsg3(sd_dbglvl, "set blocked=%s from %s:%d\n", dev->print_blocked(), file, line);
256 * Unblock the device, and wake up anyone who went to sleep.
257 * Enter: device locked
258 * Exit: device locked
260 void _unblock_device(const char *file, int line, DEVICE *dev)
262 Dmsg3(sd_dbglvl, "unblock %s from %s:%d\n", dev->print_blocked(), file, line);
263 ASSERT(dev->blocked());
264 dev->set_blocked(BST_NOT_BLOCKED);
265 clear_thread_id(dev->no_wait_id);
266 if (dev->num_waiting > 0) {
267 pthread_cond_broadcast(&dev->wait); /* wake them up */
272 * Enter with device locked and blocked
273 * Exit with device unlocked and blocked by us.
275 void _steal_device_lock(const char *file, int line, DEVICE *dev, bsteal_lock_t *hold, int state)
278 Dmsg3(sd_dbglvl, "steal lock. old=%s from %s:%d\n", dev->print_blocked(),
280 hold->dev_blocked = dev->blocked();
281 hold->dev_prev_blocked = dev->dev_prev_blocked;
282 hold->no_wait_id = dev->no_wait_id;
283 dev->set_blocked(state);
284 Dmsg1(sd_dbglvl, "steal lock. new=%s\n", dev->print_blocked());
285 dev->no_wait_id = pthread_self();
290 * Enter with device blocked by us but not locked
291 * Exit with device locked, and blocked by previous owner
293 void _give_back_device_lock(const char *file, int line, DEVICE *dev, bsteal_lock_t *hold)
295 Dmsg3(sd_dbglvl, "return lock. old=%s from %s:%d\n",
296 dev->print_blocked(), file, line);
298 dev->set_blocked(hold->dev_blocked);
299 dev->dev_prev_blocked = hold->dev_prev_blocked;
300 dev->no_wait_id = hold->no_wait_id;
301 Dmsg1(sd_dbglvl, "return lock. new=%s\n", dev->print_blocked());
302 if (dev->num_waiting > 0) {
303 pthread_cond_broadcast(&dev->wait); /* wake them up */
307 const char *DEVICE::print_blocked() const
310 case BST_NOT_BLOCKED:
311 return "BST_NOT_BLOCKED";
313 return "BST_UNMOUNTED";
314 case BST_WAITING_FOR_SYSOP:
315 return "BST_WAITING_FOR_SYSOP";
316 case BST_DOING_ACQUIRE:
317 return "BST_DOING_ACQUIRE";
318 case BST_WRITING_LABEL:
319 return "BST_WRITING_LABEL";
320 case BST_UNMOUNTED_WAITING_FOR_SYSOP:
321 return "BST_UNMOUNTED_WAITING_FOR_SYSOP";
325 return "BST_DESPOOLING";
327 return _("unknown blocked code");
333 * Check if the device is blocked or not
335 bool is_device_unmounted(DEVICE *dev)
338 int blocked = dev->blocked();
339 stat = (blocked == BST_UNMOUNTED) ||
340 (blocked == BST_UNMOUNTED_WAITING_FOR_SYSOP);