2 Bacula® - The Network Backup Solution
4 Copyright (C) 2000-2009 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(locked) "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.
64 * Can be called with locked true, which means the
65 * dlock is already set
67 * A lock is normally set when modifying the device structure.
68 * A r_lock is normally acquired when you want to block the device
69 * i.e. it will wait until the device is not blocked.
70 * A block is normally set during long operations like writing to
72 * If you are writing the device, you will normally block and
74 * A lock cannot be violated. No other thread can touch the
75 * device while a lock is set.
76 * When a block is set, every thread accept the thread that set
77 * the block will block if r_dlock is called.
78 * A device can be blocked for multiple reasons, labeling, writing,
79 * acquiring (opening) the device, waiting for the operator, unmounted,
81 * Under certain conditions the block that is set on a device can be
82 * stolen and the device can be used by another thread. For example,
83 * a device is blocked because it is waiting for the operator to
84 * mount a tape. The operator can then unmount the device, and label
85 * a tape, re-mount it, give back the block, and the job will continue.
90 * DEVICE::dlock() does P(m_mutex) (in dev.h)
91 * DEVICE::dunlock() does V(m_mutex)
93 * DEVICE::r_dlock(locked) allows locking the device when this thread
94 * already has the device blocked.
97 * if blocked and not same thread that locked
99 * leaves device locked
101 * DEVICE::r_dunlock() unlocks but does not unblock
104 * DEVICE::dblock(why) does
105 * r_dlock(); (recursive device lock)
106 * block_device(this, why)
109 * DEVICE::dunblock does
114 * block_device() does (must be locked and not blocked at entry)
118 * unblock_device() does (must be blocked at entry)
121 * set unblocked status
124 * pthread_cond_broadcast
126 * steal_device_lock() does (must be locked and blocked at entry)
128 * set new blocked status
132 * give_back_device_lock() does (must be blocked but not locked)
134 * reset blocked status
135 * save previous blocked
138 * pthread_cond_broadcast
143 void DEVICE::dblock(int why)
145 r_dlock(); /* need recursive lock to block */
146 block_device(this, why);
150 void DEVICE::dunblock(bool locked)
155 unblock_device(this);
161 void DCR::_dlock(const char *file, int line)
163 dev->_dlock(file, line);
166 void DCR::_dunlock(const char *file, int line)
168 m_dev_locked = false;
169 dev->_dunlock(file, line);
173 void DEVICE::_dlock(const char *file, int line)
175 Dmsg3(sd_dbglvl, "dlock from %s:%d precnt=%d\n", file, line, m_count);
176 /* Note, this *really* should be protected by a mutex, but
177 * since it is only debug code we don't worry too much.
179 if (m_count > 0 && pthread_equal(m_pid, pthread_self())) {
180 Dmsg4(sd_dbglvl, "Possible DEADLOCK!! lock held by JobId=%u from %s:%d m_count=%d\n",
181 get_jobid_from_tid(m_pid),
182 file, line, m_count);
185 m_pid = pthread_self();
189 void DEVICE::_dunlock(const char *file, int line)
192 Dmsg3(sd_dbglvl+1, "dunlock from %s:%d postcnt=%d\n", file, line, m_count);
196 void DEVICE::_r_dunlock(const char *file, int line)
198 this->_dunlock(file, line);
205 * This is a recursive lock that checks if the device is blocked.
207 * When blocked is set, all threads EXCEPT thread with id no_wait_id
208 * must wait. The no_wait_id thread is out obtaining a new volume
209 * and preparing the label.
212 void DEVICE::_r_dlock(const char *file, int line, bool locked)
214 Dmsg3(sd_dbglvl+1, "r_dlock blked=%s from %s:%d\n", this->print_blocked(),
217 void DEVICE::r_dlock(bool locked)
222 P(m_mutex); /* this->dlock(); */
223 m_count++; /* this->dlock() */
225 if (this->blocked() && !pthread_equal(this->no_wait_id, pthread_self())) {
226 this->num_waiting++; /* indicate that I am waiting */
227 while (this->blocked()) {
229 /* thread id on Win32 may be a struct */
230 Dmsg3(sd_dbglvl, "r_dlock blked=%s no_wait=%p me=%p\n", this->print_blocked(),
231 this->no_wait_id, pthread_self());
233 if ((stat = pthread_cond_wait(&this->wait, &m_mutex)) != 0) {
236 Emsg1(M_ABORT, 0, _("pthread_cond_wait failure. ERR=%s\n"),
240 this->num_waiting--; /* no longer waiting */
245 * Block all other threads from using the device
246 * Device must already be locked. After this call,
247 * the device is blocked to any thread calling dev->r_lock(),
248 * but the device is not locked (i.e. no P on device). Also,
249 * the current thread can do slip through the dev->r_lock()
250 * calls without blocking.
252 void _block_device(const char *file, int line, DEVICE *dev, int state)
254 ASSERT(dev->blocked() == BST_NOT_BLOCKED);
255 dev->set_blocked(state); /* make other threads wait */
256 dev->no_wait_id = pthread_self(); /* allow us to continue */
257 Dmsg3(sd_dbglvl, "set blocked=%s from %s:%d\n", dev->print_blocked(), file, line);
261 * Unblock the device, and wake up anyone who went to sleep.
262 * Enter: device locked
263 * Exit: device locked
265 void _unblock_device(const char *file, int line, DEVICE *dev)
267 Dmsg3(sd_dbglvl, "unblock %s from %s:%d\n", dev->print_blocked(), file, line);
268 ASSERT(dev->blocked());
269 dev->set_blocked(BST_NOT_BLOCKED);
270 clear_thread_id(dev->no_wait_id);
271 if (dev->num_waiting > 0) {
272 pthread_cond_broadcast(&dev->wait); /* wake them up */
277 * Enter with device locked and blocked
278 * Exit with device unlocked and blocked by us.
280 void _steal_device_lock(const char *file, int line, DEVICE *dev, bsteal_lock_t *hold, int state)
283 Dmsg3(sd_dbglvl, "steal lock. old=%s from %s:%d\n", dev->print_blocked(),
285 hold->dev_blocked = dev->blocked();
286 hold->dev_prev_blocked = dev->dev_prev_blocked;
287 hold->no_wait_id = dev->no_wait_id;
288 dev->set_blocked(state);
289 Dmsg1(sd_dbglvl, "steal lock. new=%s\n", dev->print_blocked());
290 dev->no_wait_id = pthread_self();
295 * Enter with device blocked by us but not locked
296 * Exit with device locked, and blocked by previous owner
298 void _give_back_device_lock(const char *file, int line, DEVICE *dev, bsteal_lock_t *hold)
300 Dmsg3(sd_dbglvl, "return lock. old=%s from %s:%d\n",
301 dev->print_blocked(), file, line);
303 dev->set_blocked(hold->dev_blocked);
304 dev->dev_prev_blocked = hold->dev_prev_blocked;
305 dev->no_wait_id = hold->no_wait_id;
306 Dmsg1(sd_dbglvl, "return lock. new=%s\n", dev->print_blocked());
307 if (dev->num_waiting > 0) {
308 pthread_cond_broadcast(&dev->wait); /* wake them up */
312 const char *DEVICE::print_blocked() const
315 case BST_NOT_BLOCKED:
316 return "BST_NOT_BLOCKED";
318 return "BST_UNMOUNTED";
319 case BST_WAITING_FOR_SYSOP:
320 return "BST_WAITING_FOR_SYSOP";
321 case BST_DOING_ACQUIRE:
322 return "BST_DOING_ACQUIRE";
323 case BST_WRITING_LABEL:
324 return "BST_WRITING_LABEL";
325 case BST_UNMOUNTED_WAITING_FOR_SYSOP:
326 return "BST_UNMOUNTED_WAITING_FOR_SYSOP";
330 return "BST_DESPOOLING";
332 return "BST_RELEASING";
334 return _("unknown blocked code");
340 * Check if the device is blocked or not
342 bool DEVICE::is_device_unmounted()
346 stat = (blk == BST_UNMOUNTED) ||
347 (blk == BST_UNMOUNTED_WAITING_FOR_SYSOP);