589:: this allows multiple concurrent users access to the database whilst the system keeps a copy of the initial-read made by each user. When a user wants to update a record, the application determines whether another user has changed the record since it was last read. The application does this by comparing the initial-read held in memory to the database record to verify any changes made to the record. Any discrepancies between the initial-read and the database record violates concurrency rules and hence causes the system to disregard any update request. An error message is generated and the user is asked to start the update process again. It improves database performance by reducing the amount of locking required, thereby reducing the load on the database server. It works efficiently with tables that require limited updates since no users are locked out. However, some updates may fail. The downside is constant update failures due to high volumes of update requests from multiple concurrent users - it can be frustrating for users.
510:. The more coarse the lock, the higher the likelihood that the lock will stop an unrelated process from proceeding. Conversely, using a fine granularity (a larger number of locks, each protecting a fairly small amount of data) increases the overhead of the locks themselves but reduces lock contention. Granular locking where each process must hold multiple locks from a common set of locks can create subtle lock dependencies. This subtlety can increase the chance that a programmer will unknowingly introduce a
577:
occur. Pessimistic concurrency is best implemented when lock times will be short, as in programmatic processing of records. Pessimistic concurrency requires a persistent connection to the database and is not a scalable option when users are interacting with data, because records might be locked for relatively large periods of time. It is not appropriate for use in Web application development.
682:
respective locks. The first blocked lock for operation in the queue is acquired as soon as the existing blocking lock is removed from the object, and then its respective operation is executed. If a lock for operation in the queue is not blocked by any existing lock (existence of multiple compatible locks on a same object is possible concurrently), it is acquired immediately.
569:: a user who reads a record with the intention of updating it places an exclusive lock on the record to prevent other users from manipulating it. This means no one else can manipulate that record until the user releases the lock. The downside is that users can be locked out for a very long time, thereby slowing the overall system response and causing frustration.
108:, the thread simply waits ("spins") until the lock becomes available. This is efficient if threads are blocked for a short time, because it avoids the overhead of operating system process re-scheduling. It is inefficient if the lock is held for a long time, or if the progress of the thread that is holding the lock depends on preemption of the locked thread.
521:, for example, a lock could protect, in order of decreasing granularity, part of a field, a field, a record, a data page, or an entire table. Coarse granularity, such as using table locks, tends to give the best performance for a single user, whereas fine granularity, such as record locks, tends to give the best performance for multiple users.
481:: this occurs whenever one process or thread attempts to acquire a lock held by another process or thread. The more fine-grained the available locks, the less likely one process/thread will request a lock held by the other. (For example, locking a row rather than the entire table, or locking a cell rather than the entire row);
865:
has been withdrawn from the first account, but not yet deposited into the other account: money has gone missing from the system. This problem can only be fixed completely by putting locks on both accounts prior to changing either one, but then the locks have to be placed according to some arbitrary,
787:
In most cases, proper locking depends on the CPU providing a method of atomic instruction stream synchronization (for example, the addition or deletion of an item into a pipeline requires that all contemporaneous operations needing to add or delete other items in the pipe be suspended during the
681:
indicates incompatibility, i.e, a case when a lock of the first type (in left column) on an object blocks a lock of the second type (in top row) from being acquired on the same object (by another transaction). An object typically has a queue of waiting requested (by transactions) operations with
596:
Where to use optimistic locking: this is appropriate in environments where there is low contention for data, or where read-only access to data is required. Optimistic concurrency is used extensively in .NET to address the needs of mobile and disconnected applications, where locking data rows for
576:
Where to use pessimistic locking: this is mainly used in environments where data-contention (the degree of users request to the database system at any one time) is heavy; where the cost of protecting data through locks is less than the cost of rolling back transactions, if concurrency conflicts
542:
ensures that the concurrent execution of the transaction turns out equivalent to some serial ordering of the transaction. However, deadlocks become an unfortunate side-effect of locking in databases. Deadlocks are either prevented by pre-determining the locking order between transactions or are
723:
Instability: the optimal balance between lock overhead and lock contention can be unique to the problem domain (application) and sensitive to design, implementation, and even low-level system architectural changes. These balances may change over the life cycle of an application and may entail
206:
The above example does not guarantee that the task has the lock, since more than one task can be testing the lock at the same time. Since both tasks will detect that the lock is free, both tasks will attempt to set the lock, not knowing that the other task is also setting the lock.
788:
manipulation of the memory content required to add or delete the specific item). Therefore, an application can often be more robust when it recognizes the burdens it places upon an operating system and is capable of graciously recognizing the reporting of impossible demands.
727:
Composability: locks are only composable (e.g., managing multiple concurrent locks in order to atomically delete item X from table A and insert X into table B) with relatively elaborate (overhead) software support and perfect adherence by applications programming to rigorous
701:
Contention: some threads/processes have to wait until a lock (or a whole set of locks) is released. If one of the threads holding a lock dies, stalls, blocks, or enters an infinite loop, other threads waiting for the lock may wait indefinitely until the computer is
1189:
that sometimes uses the same basic implementation as the binary semaphore. However, they differ in how they are used. While a binary semaphore may be colloquially referred to as a mutex, a true mutex has a more specific use-case and definition, in that only the
472:: the extra resources for using locks, like the memory space allocated for locks, the CPU time to initialize and destroy locks, and the time for acquiring or releasing locks. The more locks a program uses, the more overhead associated with the usage;
85:. It provides exclusive access to the locked data. Other schemes also provide shared access for reading data. Other widely implemented access modes are exclusive, intend-to-exclude and intend-to-upgrade.
502:. The granularity is a measure of the amount of data the lock is protecting. In general, choosing a coarse granularity (a small number of locks, each protecting a large segment of data) results in less
1924:
780:. However, such alternative methods often require that the actual lock mechanisms be implemented at a more fundamental level of the operating software. Therefore, they may only relieve the
230:. (The most common strategy is to standardize the lock acquisition sequences so that combinations of inter-dependent locks are always acquired in a specifically defined "cascade" order.)
597:
prolonged periods of time would be infeasible. Also, maintaining record locks requires a persistent connection to the database server, which is not possible in disconnected applications.
608:
Several variations and refinements of these major lock types exist, with respective variations of blocking behavior. If a first lock blocks another lock, the two locks are called
1201:: If the mutex knows who locked it and is supposed to unlock it, it is possible to promote the priority of that task whenever a higher-priority task starts waiting on the mutex.
1628:
1607:
1434:
A protected object provides coordinated access to shared data, through calls on its visible protected operations, which can be protected subprograms or protected entries.
1649:
800:": it is hard to combine small, correct lock-based modules into equally correct larger programs without modifying the modules or at least knowing about their internals.
709:
Overhead: the use of locks adds overhead for each access to a resource, even when the chances for collision are very rare. (However, any chance for such collisions is a
134:
1586:
506:
when a single process is accessing the protected data, but worse performance when multiple processes are running concurrently. This is because of increased
489:: the situation when each of at least two tasks is waiting for a lock that the other task holds. Unless something is done, the two tasks will wait forever.
145:
shared-memory machines. Proper support for locks in a multiprocessor environment can require quite complex hardware or software support, with substantial
812:
that allows multiple concurrent clients to deposit or withdraw money to an account, and give an algorithm to transfer money from one account to another.
1565:
1129:, which can either be empty or contain a value, typically a reference to a resource. A thread that wants to use the resource âtakesâ the value of the
538:
can be used as a means of ensuring transaction synchronicity. i.e. when making transaction processing concurrent (interleaving transactions), using
1485:
1446:
89:
493:
There is a tradeoff between decreasing lock overhead and decreasing lock contention when choosing the number of locks in synchronization.
892:
1204:
Premature task termination: Mutexes may also provide deletion safety, where the task holding the mutex cannot be accidentally deleted.
17:
127:". These instructions allow a single process to test if the lock is free, and if free, acquire the lock in a single atomic operation.
2594:
1951:
784:
level from the details of implementing locks, with the problems listed above still needing to be dealt with beneath the application.
547:. An alternate to locking for database synchronicity while avoiding deadlocks involves the use of totally ordered global timestamps.
1342:
797:
1710:
156:
is required is because of concurrency, where more than one task executes the same logic. For example, consider the following
1194:
that locked the mutex is supposed to unlock it. This constraint aims to handle some potential problems of using semaphores:
111:
Locks typically require hardware support for efficient implementation. This support usually takes the form of one or more
70:, where each thread cooperates by acquiring the lock before accessing the corresponding data. Some systems also implement
716:
Debugging: bugs associated with locks are time dependent and can be very subtle and extremely hard to replicate, such as
689:
In some publications, the table entries are simply marked "compatible" or "incompatible", or respectively "yes" or "no".
58:
policies, and with a variety of possible methods there exist multiple unique implementations for different applications.
1174:
2476:
1248:
773:
752:: all other threads have to wait if a thread holding a lock is descheduled due to a time-slice interrupt or page fault.
227:
146:
1684:
2589:
2501:
1882:
1848:
1186:
928:
1317:
1137:
results in the thread blocking until the resource is available. As an alternative to locking, an implementation of
734:: a low-priority thread/process holding a common lock can prevent high-priority threads/processes from proceeding.
498:
2449:
2274:
2073:
1397:
1371:
884:
to.lock() from.lock() from.withdraw(amount) to.deposit(amount) from.unlock() to.unlock()
226:. A number of strategies can be used to avoid or recover from deadlocks or livelocks, both at design-time and at
2167:
974:
742:
can be used on uniprocessor systems to minimize the worst-case priority-inversion duration, as well as prevent
234:
1868:
1834:
2297:
2257:
1944:
1156:
1138:
1044:
1006:
805:
761:
2584:
2267:
2262:
1055:
1024:
833:
deposit(n: Integer) mutex.lock() balance â balance + n mutex.unlock()
769:
1541:
1221:
Accidental release: An error is raised on the release of the mutex if the releasing task is not its owner.
2542:
2380:
1500:
1102:
1092:
998:
951:
standard is supported by some compilers, and allows critical sections to be specified using pragmas. The
743:
717:
485:
429:
219:
2157:
1208:
913:
904:
854:
transfer(from: Account, to: Account, amount: Integer) from.withdraw(amount) to.deposit(amount)
518:
51:
1133:, leaving it empty, and puts it back when it is finished. Attempting to take a resource from an empty
2365:
2360:
2187:
1759:
1253:
1160:
1144:
1010:
932:
739:
112:
101:
47:
916:
provides protected objects that have visible protected subprograms or entries as well as rendezvous.
2405:
2370:
2337:
1987:
1937:
1027:
NSLock, NSRecursiveLock, and NSConditionLock along with the NSLocking protocol for locking as well.
920:
554:
on a databaseâthe purpose is to prevent lost updates and dirty reads. The two types of locking are
157:
1282:
2307:
2279:
2217:
2202:
2118:
1960:
1263:
465:
Before being introduced to lock granularity, one needs to understand three concepts about locks:
432:, C# can also synchronize entire methods, by using the MethodImplOptions.Synchronized attribute.
212:
82:
857:
In a concurrent program, this algorithm is incorrect because when one thread is halfway through
2284:
2212:
2162:
1997:
1520:
1238:
2563:
2466:
2312:
2292:
2237:
1112:
208:
97:
2375:
2332:
2327:
2317:
2227:
1805:
777:
735:
697:
Lock-based resource protection and thread/process synchronization have many disadvantages:
93:
1321:
8:
2415:
2400:
2395:
2252:
2137:
2083:
1296:
984:
757:
616:. Often, lock types blocking interactions are presented in the technical literature by a
477:
55:
1461:
1350:
2537:
2516:
2425:
2322:
2172:
2065:
2017:
1979:
1874:
1840:
1780:
1479:
1440:
1419:
1198:
801:
765:
731:
585:
75:
940:
2207:
2050:
2040:
2035:
2007:
2002:
1878:
1844:
964:
539:
1714:
963:
attribute of methods to be synchronized, but this is specific to COM objects in the
2506:
2247:
2192:
2113:
2103:
2093:
2088:
1545:
1258:
1233:
1191:
1148:
1096:
1048:
971:
compiler. C and C++ can easily access any native operating system locking features.
924:
153:
124:
43:
31:
2496:
2442:
2420:
2197:
2152:
2123:
2098:
2078:
2025:
1992:
1968:
1215:
551:
535:
530:
1736:
2481:
2342:
2045:
2030:
710:
544:
142:
1670:
1086:
137:
of instructionsâusing special instructions or instruction prefixes to disable
104:
requesting the lock until it is allowed to access the locked resource. With a
2578:
2302:
2147:
2108:
2055:
1207:
Termination deadlock: If a mutex-holding task terminates for any reason, the
952:
703:
120:
2558:
2521:
2410:
2385:
2177:
1929:
1864:
1830:
1688:
1243:
968:
956:
130:
116:
887:
This solution gets more complicated when more locks are involved, and the
768:
can avoid the biggest problem: deadlocks. Alternatives to locking include
74:, where attempting unauthorized access to a locked resource will force an
2511:
2486:
2471:
2390:
2222:
1016:
749:
215:
are possible substitutes if atomic locking operations are not available.
808:) gives the following example of a banking application: design a class
796:
One of lock-based programming's biggest problems is that "locks don't
27:
Synchronization mechanism for enforcing limits on access to a resource
2491:
1346:
138:
223:
105:
1211:
can release the mutex and signal waiting tasks of this condition.
1122:
1066:
981:
keyword on a thread to ensure its exclusive access to a resource.
944:
909:
Programming languages vary in their support for synchronization:
891:
function needs to know about all of the locks, so they cannot be
620:. The following is an example with the common, major lock types:
1898:
550:
There are mechanisms employed to manage the actions of multiple
50:
that prevents state from being modified or accessed by multiple
1343:"Designing Data Tier Components and Passing Data Through Tiers"
948:
760:
strategies avoid some or all of these problems. For example, a
425:
can lead to problems if the instance can be accessed publicly.
1182:
936:
815:
The lock-based solution to the first part of the problem is:
233:
Some languages do support locks syntactically. An example in
840:
The second part of the problem is much more complicated. A
1806:"Shared-State Concurrency - The Rust Programming Language"
1405:
Beautiful Code: Leading
Programmers Explain How They Think
1152:
1125:
implements locking via a mutable data structure called an
1119:
prefix on certain operations to guarantee their atomicity.
872:
transfer(from: Account, to: Account, amount: Integer)
88:
Another way to classify locks is by what happens when the
1218:
multiple times as it unlocks it an equal number of times.
1030:
1013:
and libraries featuring concurrency-safe data structures.
380:// Only one thread at a time may execute this statement.
320:// Only one thread at a time may execute this statement.
92:
prevents the progress of a thread. Most locking designs
1833:(August 2013). "Basic concurrency: threads and MVars".
738:
can be used to reduce priority-inversion duration. The
1023:
to put locks on blocks of code and also provides the
1823:
1372:"Lock Based Concurrency Control Protocol in DBMS"
1155:package. It can be used for locking code blocks,
141:temporarilyâbut this technique does not work for
2576:
1867:(August 2013). "Software transactional memory".
1214:Recursion deadlock: a task is allowed to lock a
1175:Semaphore (programming) § Semaphores vs. mutexes
1870:Parallel and Concurrent Programming in Haskell
1836:Parallel and Concurrent Programming in Haskell
1945:
1711:"Thread Synchronization Mechanisms in Python"
1459:
1417:
1297:"ThreadPoolPriority, and MethodImplAttribute"
78:in the entity attempting to make the access.
1959:
1395:
1069:standard (ISO/IEC 1539-1:2010) provides the
1033:provides a file-based locking as well as a
837:withdraw(n: Integer) deposit(ân)
1484:: CS1 maint: numeric names: authors list (
1445:: CS1 maint: numeric names: authors list (
603:
1952:
1938:
724:tremendous changes to update (re-balance).
1760:"Programming Ruby: Threads and Processes"
1734:
1167:
1498:
1462:"Example of Tasking and Synchronization"
1318:"C# From a Java Developer's Perspective"
791:
54:at once. Locks enforce mutual exclusion
1925:Tutorial on Locks and Critical Sections
1737:"Coarrays in the next Fortran Standard"
1420:"Protected Units and Protected Objects"
496:An important property of a lock is its
133:architectures have the option of using
14:
2577:
1863:
1829:
1403:. In Wilson, Greg; Oram, Andy (eds.).
861:, another might observe a state where
81:The simplest type of lock is a binary
1933:
1708:
1073:derived type in the intrinsic module
866:global ordering to prevent deadlock:
218:Careless use of locks can result in
898:
24:
1899:"sync package - sync - pkg.go.dev"
1249:Lock-free and wait-free algorithms
880:from.lock() to.lock()
878:// arbitrary ordering on the locks
251:// This is a monitor of an account
25:
2606:
1918:
929:application programming interface
524:
2595:Programming language comparisons
1173:This section is an excerpt from
692:
2450:Enterprise Integration Patterns
1891:
1857:
1798:
1773:
1752:
1728:
1702:
1677:
1663:
1642:
1621:
1600:
1579:
1558:
1534:
1513:
1283:"lock Statement (C# Reference)"
1650:"NSLocking Protocol Reference"
1492:
1466:Ada 2005 Reference Manual
1453:
1424:Ada 2005 Reference Manual
1411:
1389:
1364:
1335:
1310:
1289:
1275:
460:
13:
1:
1499:Marshall, Dave (March 1999).
1349:. August 2002. Archived from
1269:
1151:object in standard's library
1139:software transactional memory
923:standard provides a standard
806:software transactional memory
1709:Lundh, Fredrik (July 2007).
1396:Peyton Jones, Simon (2007).
770:non-blocking synchronization
7:
2543:Portland Pattern Repository
1629:"NSConditionLock Reference"
1608:"NSRecursiveLock Reference"
1566:"Apple Threading Reference"
1227:
955:API provides lock support.
776:programming techniques and
10:
2611:
1172:
905:Barrier (computer science)
902:
612:; otherwise the locks are
528:
519:database management system
18:Locking (computer science)
2551:
2530:
2459:
2434:
2351:
2236:
2136:
2064:
2016:
1978:
1967:
1781:"std::sync::Mutex - Rust"
1254:Monitor (synchronization)
740:priority ceiling protocol
624:Lock compatibility table
135:uninterruptible sequences
48:synchronization primitive
2590:Software design patterns
2168:Event-based asynchronous
1961:Software design patterns
1501:"Mutual Exclusion Locks"
844:routine that is correct
618:Lock compatibility table
604:Lock compatibility table
434:
239:
162:
61:
2074:Chain of responsibility
1398:"Beautiful concurrency"
1264:Read/write lock pattern
846:for sequential programs
675:indicates compatibility
2213:Scheduled-task pattern
2163:Double-checked locking
1239:Double-checked locking
1168:Mutexes vs. semaphores
1099:object and no keyword.
935:. The current ISO/IEC
115:instructions such as "
2564:Architectural pattern
2467:Christopher Alexander
1147:provides a low-level
1113:x86 assembly language
1095:provides a low-level
1047:provides a low-level
1019:provides the keyword
1005:to lock code blocks,
1001:provides the keyword
825:balance: Integer
792:Lack of composability
66:Generally, locks are
2376:Dependency injection
2333:Inversion of control
2328:Data transfer object
2228:Thread-local storage
1523:. msdn.microsoft.com
941:threading facilities
778:transactional memory
736:Priority inheritance
213:Peterson's algorithm
186:// lock free, set it
52:threads of execution
2585:Concurrency control
2381:Intercepting filter
1460:ISO/IEC 8652:2007.
1418:ISO/IEC 8652:2007.
985:Visual Basic (.NET)
758:concurrency control
625:
567:Pessimistic locking
556:pessimistic locking
56:concurrency control
2538:The Hillside Group
2323:Data access object
2173:Guarded suspension
2158:Binding properties
1735:John Reid (2010).
1587:"NSLock Reference"
1299:. MSDN. p. ??
1199:Priority inversion
991:keyword like C#'s
939:standard supports
802:Simon Peyton Jones
766:serializing tokens
732:Priority inversion
623:
586:Optimistic locking
560:optimistic locking
2572:
2571:
2366:Business delegate
2298:Publishâsubscribe
2132:
2131:
1810:doc.rust-lang.org
1785:doc.rust-lang.org
1685:"The Mutex class"
1542:"Synchronization"
1187:locking mechanism
1085:statements since
1051:mechanism with a
967:architecture and
669:
668:
16:(Redirected from
2602:
2371:Composite entity
2248:Front controller
1988:Abstract factory
1976:
1975:
1954:
1947:
1940:
1931:
1930:
1913:
1912:
1910:
1909:
1895:
1889:
1888:
1861:
1855:
1854:
1827:
1821:
1820:
1818:
1816:
1802:
1796:
1795:
1793:
1791:
1777:
1771:
1770:
1768:
1767:
1756:
1750:
1749:
1747:
1746:
1741:
1732:
1726:
1725:
1723:
1722:
1713:. Archived from
1706:
1700:
1699:
1697:
1696:
1687:. Archived from
1681:
1675:
1674:
1667:
1661:
1660:
1658:
1657:
1646:
1640:
1639:
1637:
1636:
1625:
1619:
1618:
1616:
1615:
1604:
1598:
1597:
1595:
1594:
1583:
1577:
1576:
1574:
1573:
1562:
1556:
1555:
1553:
1552:
1546:Sun Microsystems
1538:
1532:
1531:
1529:
1528:
1517:
1511:
1510:
1508:
1507:
1496:
1490:
1489:
1483:
1475:
1473:
1472:
1457:
1451:
1450:
1444:
1436:
1431:
1430:
1415:
1409:
1408:
1402:
1393:
1387:
1386:
1384:
1383:
1368:
1362:
1361:
1359:
1358:
1339:
1333:
1332:
1330:
1329:
1320:. Archived from
1314:
1308:
1307:
1305:
1304:
1293:
1287:
1286:
1279:
1259:Mutual exclusion
1234:Critical section
1136:
1132:
1128:
1118:
1108:
1084:
1080:
1076:
1072:
1061:
1054:
1040:
1036:
1022:
1004:
994:
990:
980:
962:
925:mutual exclusion
899:Language support
890:
876:from < to
864:
860:
843:
829:mutex: Lock
811:
804:(an advocate of
626:
622:
552:concurrent users
545:waits-for graphs
456:
453:
450:
447:
444:
441:
438:
424:
417:
414:
411:
408:
405:
402:
399:
396:
393:
390:
387:
384:
381:
378:
375:
372:
369:
366:
363:
360:
357:
354:
351:
348:
345:
342:
339:
336:
333:
330:
327:
324:
321:
318:
315:
312:
309:
306:
303:
300:
297:
294:
291:
288:
285:
282:
279:
276:
273:
270:
267:
264:
261:
258:
255:
252:
249:
246:
243:
202:
199:
196:
193:
190:
187:
184:
181:
178:
175:
172:
169:
166:
154:atomic operation
125:compare-and-swap
44:mutual exclusion
32:computer science
21:
2610:
2609:
2605:
2604:
2603:
2601:
2600:
2599:
2575:
2574:
2573:
2568:
2547:
2526:
2517:Douglas Schmidt
2497:Ward Cunningham
2455:
2443:Design Patterns
2430:
2421:Method chaining
2353:
2347:
2308:Service locator
2239:
2232:
2203:Readâwrite lock
2139:
2128:
2119:Template method
2060:
2012:
1970:
1963:
1958:
1921:
1916:
1907:
1905:
1897:
1896:
1892:
1885:
1862:
1858:
1851:
1828:
1824:
1814:
1812:
1804:
1803:
1799:
1789:
1787:
1779:
1778:
1774:
1765:
1763:
1758:
1757:
1753:
1744:
1742:
1739:
1733:
1729:
1720:
1718:
1707:
1703:
1694:
1692:
1683:
1682:
1678:
1669:
1668:
1664:
1655:
1653:
1648:
1647:
1643:
1634:
1632:
1627:
1626:
1622:
1613:
1611:
1606:
1605:
1601:
1592:
1590:
1585:
1584:
1580:
1571:
1569:
1564:
1563:
1559:
1550:
1548:
1540:
1539:
1535:
1526:
1524:
1519:
1518:
1514:
1505:
1503:
1497:
1493:
1477:
1476:
1470:
1468:
1458:
1454:
1438:
1437:
1428:
1426:
1416:
1412:
1400:
1394:
1390:
1381:
1379:
1370:
1369:
1365:
1356:
1354:
1341:
1340:
1336:
1327:
1325:
1316:
1315:
1311:
1302:
1300:
1295:
1294:
1290:
1281:
1280:
1276:
1272:
1230:
1225:
1224:
1216:reentrant mutex
1178:
1170:
1134:
1130:
1126:
1116:
1106:
1082:
1078:
1075:iso_fortran_env
1074:
1070:
1059:
1052:
1038:
1034:
1020:
1002:
992:
988:
978:
960:
907:
901:
888:
885:
862:
858:
855:
841:
838:
809:
794:
695:
606:
543:detected using
533:
531:Lock (database)
527:
508:lock contention
463:
458:
457:
454:
451:
448:
445:
442:
439:
436:
422:
419:
418:
415:
412:
409:
406:
403:
400:
397:
394:
391:
388:
385:
382:
379:
376:
373:
370:
367:
364:
361:
358:
355:
352:
349:
346:
343:
340:
337:
334:
331:
328:
325:
322:
319:
316:
313:
310:
307:
304:
301:
298:
295:
292:
289:
286:
283:
280:
277:
274:
271:
268:
265:
262:
259:
256:
253:
250:
247:
244:
241:
204:
203:
200:
197:
194:
191:
188:
185:
182:
179:
176:
173:
170:
167:
164:
147:synchronization
72:mandatory locks
64:
28:
23:
22:
15:
12:
11:
5:
2608:
2598:
2597:
2592:
2587:
2570:
2569:
2567:
2566:
2561:
2555:
2553:
2549:
2548:
2546:
2545:
2540:
2534:
2532:
2528:
2527:
2525:
2524:
2519:
2514:
2509:
2504:
2499:
2494:
2489:
2484:
2482:John Vlissides
2479:
2474:
2469:
2463:
2461:
2457:
2456:
2454:
2453:
2446:
2438:
2436:
2432:
2431:
2429:
2428:
2423:
2418:
2413:
2408:
2403:
2398:
2393:
2388:
2383:
2378:
2373:
2368:
2363:
2357:
2355:
2349:
2348:
2346:
2345:
2340:
2335:
2330:
2325:
2320:
2315:
2310:
2305:
2300:
2295:
2290:
2282:
2277:
2272:
2271:
2270:
2265:
2255:
2250:
2244:
2242:
2234:
2233:
2231:
2230:
2225:
2220:
2215:
2210:
2205:
2200:
2195:
2190:
2185:
2180:
2175:
2170:
2165:
2160:
2155:
2150:
2144:
2142:
2134:
2133:
2130:
2129:
2127:
2126:
2121:
2116:
2111:
2106:
2101:
2096:
2091:
2086:
2081:
2076:
2070:
2068:
2062:
2061:
2059:
2058:
2053:
2048:
2043:
2038:
2033:
2028:
2022:
2020:
2014:
2013:
2011:
2010:
2005:
2000:
1998:Factory method
1995:
1990:
1984:
1982:
1973:
1965:
1964:
1957:
1956:
1949:
1942:
1934:
1928:
1927:
1920:
1919:External links
1917:
1915:
1914:
1890:
1883:
1875:OâReilly Media
1856:
1849:
1841:OâReilly Media
1822:
1797:
1772:
1751:
1727:
1701:
1676:
1662:
1641:
1620:
1599:
1578:
1557:
1533:
1512:
1491:
1452:
1410:
1388:
1363:
1334:
1309:
1288:
1273:
1271:
1268:
1267:
1266:
1261:
1256:
1251:
1246:
1241:
1236:
1229:
1226:
1223:
1222:
1219:
1212:
1205:
1202:
1179:
1171:
1169:
1166:
1165:
1164:
1142:
1120:
1110:
1107:Mutex<T>
1100:
1090:
1063:
1042:
1028:
1014:
996:
982:
972:
917:
900:
897:
868:
850:
817:
793:
790:
772:methods, like
754:
753:
747:
729:
725:
721:
714:
711:race condition
707:
694:
691:
684:
683:
676:
667:
666:
661:
656:
652:
651:
646:
641:
637:
636:
633:
630:
605:
602:
601:
600:
599:
598:
591:
590:
581:
580:
579:
578:
571:
570:
540:2-phased locks
536:Database locks
529:Main article:
526:
525:Database locks
523:
491:
490:
482:
473:
462:
459:
435:
240:
163:
152:The reason an
143:multiprocessor
68:advisory locks
63:
60:
26:
9:
6:
4:
3:
2:
2607:
2596:
2593:
2591:
2588:
2586:
2583:
2582:
2580:
2565:
2562:
2560:
2557:
2556:
2554:
2550:
2544:
2541:
2539:
2536:
2535:
2533:
2529:
2523:
2520:
2518:
2515:
2513:
2510:
2508:
2507:Robert Martin
2505:
2503:
2502:Martin Fowler
2500:
2498:
2495:
2493:
2490:
2488:
2485:
2483:
2480:
2478:
2477:Ralph Johnson
2475:
2473:
2470:
2468:
2465:
2464:
2462:
2458:
2452:
2451:
2447:
2445:
2444:
2440:
2439:
2437:
2433:
2427:
2424:
2422:
2419:
2417:
2414:
2412:
2409:
2407:
2404:
2402:
2399:
2397:
2394:
2392:
2389:
2387:
2384:
2382:
2379:
2377:
2374:
2372:
2369:
2367:
2364:
2362:
2359:
2358:
2356:
2350:
2344:
2341:
2339:
2336:
2334:
2331:
2329:
2326:
2324:
2321:
2319:
2316:
2314:
2313:Active record
2311:
2309:
2306:
2304:
2303:Naked objects
2301:
2299:
2296:
2294:
2293:Specification
2291:
2289:
2287:
2283:
2281:
2278:
2276:
2273:
2269:
2266:
2264:
2261:
2260:
2259:
2256:
2254:
2251:
2249:
2246:
2245:
2243:
2241:
2238:Architectural
2235:
2229:
2226:
2224:
2221:
2219:
2216:
2214:
2211:
2209:
2206:
2204:
2201:
2199:
2196:
2194:
2191:
2189:
2186:
2184:
2181:
2179:
2176:
2174:
2171:
2169:
2166:
2164:
2161:
2159:
2156:
2154:
2151:
2149:
2148:Active object
2146:
2145:
2143:
2141:
2135:
2125:
2122:
2120:
2117:
2115:
2112:
2110:
2107:
2105:
2102:
2100:
2097:
2095:
2092:
2090:
2087:
2085:
2082:
2080:
2077:
2075:
2072:
2071:
2069:
2067:
2063:
2057:
2054:
2052:
2049:
2047:
2044:
2042:
2039:
2037:
2034:
2032:
2029:
2027:
2024:
2023:
2021:
2019:
2015:
2009:
2006:
2004:
2001:
1999:
1996:
1994:
1991:
1989:
1986:
1985:
1983:
1981:
1977:
1974:
1972:
1966:
1962:
1955:
1950:
1948:
1943:
1941:
1936:
1935:
1932:
1926:
1923:
1922:
1904:
1900:
1894:
1886:
1884:9781449335946
1880:
1876:
1872:
1871:
1866:
1865:Marlow, Simon
1860:
1852:
1850:9781449335946
1846:
1842:
1838:
1837:
1832:
1831:Marlow, Simon
1826:
1811:
1807:
1801:
1786:
1782:
1776:
1761:
1755:
1738:
1731:
1717:on 2020-11-01
1716:
1712:
1705:
1691:on 2017-07-04
1690:
1686:
1680:
1672:
1666:
1651:
1645:
1630:
1624:
1609:
1603:
1588:
1582:
1567:
1561:
1547:
1543:
1537:
1522:
1521:"Synchronize"
1516:
1502:
1495:
1487:
1481:
1467:
1463:
1456:
1448:
1442:
1435:
1425:
1421:
1414:
1406:
1399:
1392:
1377:
1376:GeeksforGeeks
1373:
1367:
1353:on 2008-05-08
1352:
1348:
1344:
1338:
1324:on 2013-01-02
1323:
1319:
1313:
1298:
1292:
1284:
1278:
1274:
1265:
1262:
1260:
1257:
1255:
1252:
1250:
1247:
1245:
1242:
1240:
1237:
1235:
1232:
1231:
1220:
1217:
1213:
1210:
1206:
1203:
1200:
1197:
1196:
1195:
1193:
1188:
1184:
1176:
1162:
1158:
1154:
1150:
1146:
1143:
1140:
1124:
1121:
1115:provides the
1114:
1111:
1105:provides the
1104:
1101:
1098:
1094:
1091:
1088:
1068:
1064:
1057:
1050:
1046:
1043:
1037:class in the
1032:
1029:
1026:
1021:@synchronized
1018:
1015:
1012:
1008:
1000:
997:
986:
983:
977:provides the
976:
973:
970:
966:
959:provides the
958:
954:
953:POSIX pthread
950:
946:
942:
938:
934:
930:
926:
922:
918:
915:
912:
911:
910:
906:
896:
894:
883:
879:
875:
871:
867:
853:
849:
847:
836:
832:
828:
824:
821:Account:
820:
816:
813:
807:
803:
799:
789:
785:
783:
779:
775:
771:
767:
763:
759:
751:
748:
745:
741:
737:
733:
730:
726:
722:
719:
715:
712:
708:
705:
700:
699:
698:
693:Disadvantages
690:
688:
680:
677:
674:
671:
670:
665:
662:
660:
657:
654:
653:
650:
647:
645:
642:
639:
638:
634:
631:
628:
627:
621:
619:
615:
611:
595:
594:
593:
592:
588:
587:
583:
582:
575:
574:
573:
572:
568:
565:
564:
563:
561:
557:
553:
548:
546:
541:
537:
532:
522:
520:
515:
513:
509:
505:
504:lock overhead
501:
500:
494:
488:
487:
483:
480:
479:
474:
471:
470:lock overhead
468:
467:
466:
433:
431:
426:
238:
236:
231:
229:
225:
221:
216:
214:
210:
161:
159:
155:
150:
148:
144:
140:
136:
132:
128:
126:
122:
121:fetch-and-add
118:
114:
109:
107:
103:
99:
95:
91:
90:lock strategy
86:
84:
79:
77:
73:
69:
59:
57:
53:
49:
45:
41:
37:
33:
19:
2559:Anti-pattern
2522:Linda Rising
2448:
2441:
2386:Lazy loading
2318:Identity map
2285:
2182:
1969:Gang of Four
1906:. Retrieved
1902:
1893:
1869:
1859:
1835:
1825:
1813:. Retrieved
1809:
1800:
1788:. Retrieved
1784:
1775:
1764:. Retrieved
1754:
1743:. Retrieved
1730:
1719:. Retrieved
1715:the original
1704:
1693:. Retrieved
1689:the original
1679:
1665:
1654:. Retrieved
1652:. Apple, inc
1644:
1633:. Retrieved
1631:. Apple, inc
1623:
1612:. Retrieved
1610:. Apple, inc
1602:
1591:. Retrieved
1589:. Apple, inc
1581:
1570:. Retrieved
1568:. Apple, inc
1560:
1549:. Retrieved
1536:
1525:. Retrieved
1515:
1504:. Retrieved
1494:
1469:. Retrieved
1465:
1455:
1433:
1427:. Retrieved
1423:
1413:
1404:
1391:
1380:. Retrieved
1378:. 2018-03-07
1375:
1366:
1355:. Retrieved
1351:the original
1337:
1326:. Retrieved
1322:the original
1312:
1301:. Retrieved
1291:
1277:
1244:File locking
1180:
1141:also exists.
1087:Fortran 2008
1065:The ISO/IEC
1003:synchronized
931:(API) since
919:The ISO/IEC
908:
886:
881:
877:
873:
869:
856:
851:
845:
839:
834:
830:
826:
822:
818:
814:
795:
786:
781:
755:
728:conventions.
704:power cycled
696:
686:
685:
678:
672:
663:
658:
648:
643:
617:
613:
610:incompatible
609:
607:
584:
566:
559:
555:
549:
534:
516:
511:
507:
503:
497:
495:
492:
484:
475:
469:
464:
427:
420:
389:_balanceLock
329:_balanceLock
281:_balanceLock
232:
217:
205:
151:
131:Uniprocessor
129:
117:test-and-set
110:
87:
80:
71:
67:
65:
39:
35:
29:
2531:Communities
2512:Jim Coplien
2487:Grady Booch
2472:Erich Gamma
2416:Type tunnel
2401:Object pool
2396:Null object
2391:Mock object
2253:Interceptor
2223:Thread pool
2138:Concurrency
2084:Interpreter
1407:. O'Reilly.
1041:extension.
1017:Objective-C
987:provides a
961:synchronize
782:application
655:write-lock
635:write-lock
499:granularity
461:Granularity
452:// do stuff
428:Similar to
2579:Categories
2426:Delegation
2361:Blackboard
2066:Behavioral
2018:Structural
1980:Creational
1908:2021-11-23
1903:pkg.go.dev
1815:3 November
1790:3 November
1766:2008-05-30
1745:2020-02-17
1721:2008-05-30
1695:2016-12-29
1656:2009-10-17
1635:2009-10-17
1614:2009-10-17
1593:2009-10-17
1572:2009-10-17
1551:2008-05-30
1527:2008-05-30
1506:2008-05-30
1471:2010-02-27
1429:2010-02-27
1382:2023-12-28
1357:2008-05-30
1328:2011-11-22
1303:2011-11-22
1270:References
969:Visual C++
957:Visual C++
903:See also:
640:read-lock
614:compatible
478:contention
443:SomeMethod
423:lock(this)
139:interrupts
2492:Kent Beck
2218:Semaphore
2208:Scheduler
2051:Flyweight
2041:Decorator
2036:Composite
2008:Singleton
2003:Prototype
1480:cite book
1441:cite book
1347:Microsoft
1071:lock_type
1060:threading
1058:from the
848:would be
774:lock-free
750:Convoying
718:deadlocks
632:read-lock
629:Lock type
421:The code
237:follows:
98:execution
83:semaphore
76:exception
2552:See also
2354:patterns
2240:patterns
2193:Proactor
2140:patterns
2114:Strategy
2104:Observer
2094:Mediator
2089:Iterator
1971:patterns
1228:See also
1077:and the
1039:pthreads
995:keyword.
989:SyncLock
927:(locks)
889:transfer
870:function
859:transfer
852:function
842:transfer
744:deadlock
687:Comment:
512:deadlock
486:deadlock
398:_balance
362:Withdraw
338:_balance
263:_balance
228:run-time
224:livelock
220:deadlock
209:Dekker's
149:issues.
106:spinlock
2406:Servant
2338:Model 2
2198:Reactor
2188:Monitor
2153:Balking
2124:Visitor
2099:Memento
2079:Command
2026:Adapter
1993:Builder
1671:"flock"
1161:objects
1157:methods
1123:Haskell
1109:struct.
1067:Fortran
1062:module.
1025:classes
1011:objects
1007:methods
965:Windows
810:Account
798:compose
368:decimal
308:decimal
302:Deposit
275:private
260:decimal
257:private
248:Account
100:of the
46:) is a
2460:People
2343:Broker
2046:Facade
2031:Bridge
1881:
1847:
1762:. 2001
1083:unlock
1045:Python
949:OpenMP
947:. The
943:since
893:hidden
863:amount
835:method
831:method
827:member
823:member
762:funnel
437:public
404:amount
371:amount
356:public
344:amount
311:amount
296:public
290:object
278:object
242:public
160:code:
123:" or "
113:atomic
102:thread
42:(from
2435:Books
2352:Other
2288:-tier
2109:State
2056:Proxy
1740:(PDF)
1401:(PDF)
1185:is a
1183:mutex
1149:Mutex
1097:mutex
1056:class
1049:mutex
1035:Mutex
945:C++11
819:class
756:Some
517:In a
476:lock
245:class
195:myPID
94:block
62:Types
40:mutex
2411:Twin
2268:MVVM
2183:Lock
2178:Join
1879:ISBN
1845:ISBN
1817:2020
1792:2020
1486:link
1447:link
1192:task
1153:sync
1135:MVar
1131:MVar
1127:MVar
1117:LOCK
1103:Rust
1093:Ruby
1079:lock
1053:Lock
999:Java
993:lock
979:lock
882:else
558:and
440:void
430:Java
383:lock
359:void
323:lock
299:void
189:lock
171:lock
119:", "
96:the
36:lock
34:, a
2280:ECS
2275:ADR
2263:MVP
2258:MVC
1159:or
1031:PHP
1009:or
937:C++
933:C11
914:Ada
764:or
293:();
287:new
222:or
211:or
38:or
30:In
2581::
1901:.
1877:.
1873:.
1843:.
1839:.
1808:.
1783:.
1544:.
1482:}}
1478:{{
1464:.
1443:}}
1439:{{
1432:.
1422:.
1374:.
1345:.
1209:OS
1181:A
1145:Go
975:C#
895:.
874:if
713:.)
562::
514:.
446:()
401:-=
341:+=
235:C#
174:==
165:if
2286:n
1953:e
1946:t
1939:v
1911:.
1887:.
1853:.
1819:.
1794:.
1769:.
1748:.
1724:.
1698:.
1673:.
1659:.
1638:.
1617:.
1596:.
1575:.
1554:.
1530:.
1509:.
1488:)
1474:.
1449:)
1385:.
1360:.
1331:.
1306:.
1285:.
1177:.
1163:.
1089:.
1081:/
921:C
746:.
720:.
706:.
679:X
673:â
664:X
659:X
649:X
644:â
455:}
449:{
416:}
413:}
410:}
407:;
395:{
392:)
386:(
377:{
374:)
365:(
353:}
350:}
347:;
335:{
332:)
326:(
317:{
314:)
305:(
284:=
272:;
269:0
266:=
254:{
201:}
198:;
192:=
183:{
180:)
177:0
168:(
158:C
20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.