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In software engineering, double-checked locking (also known as "double-checked locking optimization" [1]) is a software design pattern used to reduce the overhead of acquiring a lock by testing the locking criterion (the "lock hint") before acquiring the lock. Locking occurs only if the locking criterion check indicates that locking is required.
An RW lock allows concurrent access for read-only operations, whereas write operations require exclusive access. This means that multiple threads can read the data in parallel but an exclusive lock is needed for writing or modifying data. When a writer is writing the data, all other writers and readers will be blocked until the writer is ...
In software engineering, a spinlock is a lock that causes a thread trying to acquire it to simply wait in a loop ("spin") while repeatedly checking whether the lock is available. Since the thread remains active but is not performing a useful task, the use of such a lock is a kind of busy waiting .
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 power cycled.
In computer science, the readers–writers problems are examples of a common computing problem in concurrency. [1] There are at least three variations of the problems, which deal with situations in which many concurrent threads of execution try to access the same shared resource at one time.
A transaction is allowed to write an object if and only if it is holding a write-lock on that object. A schedule (i.e., a set of transactions) is allowed to hold multiple locks on the same object simultaneously if and only if none of those locks are write-locks. If a disallowed lock attempts on being held simultaneously, it will be blocked.
The level variables take on values up to N − 1, each representing a distinct "waiting room" before the critical section. [6] Processes advance from one room to the next, finishing in room N − 1, which is the critical section. Specifically, to acquire a lock, process i executes [4]: 22
Locks and critical sections in multiple threads. As shown in the figure, [3] in the case of mutual exclusion , one thread blocks a critical section by using locking techniques when it needs to access the shared resource, and other threads must wait their turn to enter the section. This prevents conflicts when two or more threads share the same ...