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Most current operating systems cannot prevent deadlocks. [11] When a deadlock occurs, different operating systems respond to them in different non-standard manners. Most approaches work by preventing one of the four Coffman conditions from occurring, especially the fourth one. [12] Major approaches are as follows.
Upgrading a lock from read-mode to write-mode is prone to deadlocks, since whenever two threads holding reader locks both attempt to upgrade to writer locks, a deadlock is created that can only be broken by one of the threads releasing its reader lock. The deadlock can be avoided by allowing only one thread to acquire the lock in "read-mode ...
The UNIX and Windows operating systems take this approach. [ 1 ] [ 2 ] Although using the ostrich algorithm is one of the methods of dealing with deadlocks , other effective methods exist such as dynamic avoidance, banker's algorithm , detection and recovery, and prevention.
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 detected using waits-for graphs. An alternate to locking for database synchronicity while avoiding deadlocks involves the use of totally ordered global timestamps.
Distributed deadlocks can be detected either by constructing a global wait-for graph, from local wait-for graphs at a deadlock detector or by a distributed algorithm like edge chasing. Phantom deadlocks are deadlocks that are detected in a distributed system due to system internal delays but no longer actually exist at the time of detection.
A wait-for graph in computer science is a directed graph used for deadlock detection in operating systems and relational database systems.. In computer science, a system that allows concurrent operation of multiple processes and locking of resources and which does not provide mechanisms to avoid or prevent deadlock must support a mechanism to detect deadlocks and an algorithm for recovering ...
Deadlock commonly refers to: Deadlock (locksmithing) or deadbolt, a physical door locking mechanism; Deadlock (computer science), a situation where two processes are each waiting for the other to finish; Political deadlock or gridlock, a situation of difficulty passing laws that satisfy the needs of the people
Resolving resource contention problems is one of the basic functions of operating systems. Various low-level mechanisms can be used to aid this, including locks, semaphores, mutexes and queues. The other techniques that can be applied by the operating systems include intelligent scheduling, application mapping decisions, and page coloring. [1] [2]