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Synchronization has several aspects. The most well-understood is mutual exclusion—only one thread can hold a monitor at once, so synchronizing on a monitor means that once one thread enters a synchronized block protected by a monitor, no other thread can enter a block protected by that monitor until the first thread exits the synchronized block.
Java synchronized sections, therefore, combine the functionality of both mutexes and events to ensure synchronization. Such a construct is known as a synchronization monitor. The .NET Framework also uses synchronization primitives. [10] "Synchronization is designed to be cooperative, demanding that every thread follow the synchronization ...
Another definition of monitor is a thread-safe class, object, or module that wraps around a mutex in order to safely allow access to a method or variable by more than one thread. The defining characteristic of a monitor is that its methods are executed with mutual exclusion : At each point in time, at most one thread may be executing any of its ...
In computer science, compare-and-swap (CAS) is an atomic instruction used in multithreading to achieve synchronization. It compares the contents of a memory location with a given value and, only if they are the same, modifies the contents of that memory location to a new given value. This is done as a single atomic operation.
Futures are a particular case of the synchronization primitive "events," which can be completed only once. In general, events can be reset to initial empty state and, thus, completed as many times as desired. [11] An I-var (as in the language Id) is a future with blocking semantics as defined above.
Java provides the keyword synchronized to lock code blocks, methods or objects [11] and libraries featuring concurrency-safe data structures. Objective-C provides the keyword @synchronized [ 12 ] to put locks on blocks of code and also provides the classes NSLock, [ 13 ] NSRecursiveLock, [ 14 ] and NSConditionLock [ 15 ] along with the ...
This approach is characteristic of functional programming and is also used by the string implementations in Java, C#, and Python. (See Immutable object.) The second class of approaches are synchronization-related, and are used in situations where shared state cannot be avoided: Mutual exclusion
In Java 8, native synchronization is used on the heads of the lists themselves, and the lists can mutate into small trees when they threaten to grow too large due to unfortunate hash collisions. Also, Java 8 uses the compare-and-set primitive optimistically to place the initial heads in the table, which is very fast.