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File locking is a mechanism that restricts access to a computer file, or to a region of a file, by allowing only one user or process to modify or delete it at a specific time and to prevent reading of the file while it's being modified or deleted.
Systems implement locking to prevent the classic interceding update scenario, which is a typical example of a race condition, by enforcing the serialization of update processes to any given file. The following example illustrates the interceding update problem:
Process A reads a customer record from a file containing account information, including the customer's account balance and phone number.
Process B now reads the same record from the same file, so it has its own copy.
Process A changes the account balance in its copy of the customer record and writes the record back to the file.
Process B, which still has the original stale value for the account balance in its copy of the customer record, updates the account balance and writes the customer record back to the file.
Process B has now written its stale account-balance value to the file, causing the changes made by process A to be lost.
Most operating systems support the concept of record locking, which means that individual records within any given file may be locked, thereby increasing the number of concurrent update processes. Database maintenance uses file locking, whereby it can serialize access to the entire physical file underlying a database. Although this does prevent any other process from accessing the file, it can be more efficient than individually locking many regions in the file by removing the overhead of acquiring and releasing each lock.
Poor use of file locks, like any computer lock, can result in poor performance or in deadlocks. File locking may also refer to additional security applied by a computer user either by using Windows security, NTFS permissions or by installing a third party file locking software.
Filelocking is a mechanism that restricts access to a computer file, or to a region of a file, by allowing only one user or process to modify or delete...
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Note: the byte-range advisory Network Lock Manager (NLM) protocol (added to support UNIX System V filelocking APIs) the remote quota-reporting (RQUOTAD)...
controller. SMB supports opportunistic locking (see below) on files in order to improve performance. Opportunistic locking support has changed with each Windows...
serialize concurrent access Lock (database), a feature used when multiple users access a database concurrently Filelocking, describes a mechanism that...
is unlocked. Locking can be supported by the version control system, or via informal communications between developers (aka social locking). Similar to...
computer operating systems, a file descriptor (FD, less frequently fildes) is a process-unique identifier (handle) for a file or other input/output resource...
directory structure or file metadata. For instance, filelocking cannot prevent TOCTTOU race conditions on symbolic links. Filelocking also cannot automatically...
coherency between participating computers. The DLM is used not only for filelocking but also for coordination of all disk access. VMScluster, the first clustering...
to lock names allowed the "file" locking routines to be used to implement record level locking between tasks accessing the centrally managed file *MESSAGES...
these files. Maildir was designed by Daniel J. Bernstein circa 1995, with a major goal of eliminating the need for program code to handle filelocking and...
open-source software project for content collaboration and sharing and syncing of files in distributed and federated enterprise scenarios. It allows companies and...
called deadlock. Deadlock is possible when incremental locking (locking one entity, then locking one or more additional entities) is used. To illustrate...
StorNext file system installed, these computers can read and write to the same storage volume at the same time enabling what is known as a "file-locking SAN...
implementing per-filelocking. SCSI reservations are only implemented when logical unit number (LUN) metadata is updated (e.g. file name change, file size change...
may lock the system without damaging any files, more advanced malware uses a technique called cryptoviral extortion. It encrypts the victim's files, making...
can still be accessed once the original is overwritten. Filelocking, which limits the file to one editor at a time to prevent edit conflicts. Computer...
the file itself. A consequence of the filelocking strategy is that AFS does not support large shared databases or record updating within files shared...
access or update operations on a file is executing a critical section that must be guarded with an appropriate filelocking mechanism. Database transaction...
svn:needs-lock Specifies that a file is to be checked out with file permissions set to read-only. This is designed for use with the locking mechanism...
program and data space allocation in main memory and file space in secondary storage, and filelocking during updates. When a process is terminated for any...
granularity locking (MGL) is a locking method used in database management systems (DBMS) and relational databases. In multiple granularity locking, locks are...
attempts to modify or access a file system, which can result in data corruption or privilege escalation. Filelocking provides a commonly used solution...
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