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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.
This approach does not work on multiprocessor systems where it is possible for two programs sharing a semaphore to run on different processors at the same time. To solve this problem in a multiprocessor system, a locking variable can be used to control access to the semaphore. The locking variable is manipulated using a test-and-set-lock command.
First, the async keyword indicates to C# that the method is asynchronous, meaning that it may use an arbitrary number of await expressions and will bind the result to a promise. [1]: 165–168 The return type, Task<T>, is C#'s analogue to the concept of a promise, and here is indicated to have a result value of type int.
lock contention: 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);
Event-based asynchronous: Addresses problems with the asynchronous pattern that occur in multithreaded programs. [23] No — Guarded suspension: Manages operations that require both a lock to be acquired and a precondition to be satisfied before the operation can be executed. No — Join
The goal is to introduce concurrency, by using asynchronous method invocation and a scheduler for handling requests. [2] The pattern consists of six elements: [3] A proxy, which provides an interface towards clients with publicly accessible methods. An interface which defines the method request on an active object. A list of pending requests ...
In this example, the condition being waited for is a function of the amount to be withdrawn, so it is impossible for a depositing thread to know that it made such a condition true. It makes sense in this case to allow each waiting thread into the monitor (one at a time) to check if its assertion is true.
In computer science, futures, promises, delays, and deferreds are constructs used for synchronizing program execution in some concurrent programming languages.Each is an object that acts as a proxy for a result that is initially unknown, usually because the computation of its value is not yet complete.