A Wisdom Archive on Semaphore (programming)

Threaded programs usually use synchronisation primitives provided by a high-level programming environment such as Java, or an API such as POSIX pthreads or Win32. Primitives such as mutexes and semaphores are provided to synchronize access to resources from parallel threads of execution. These primitives are usually implemented with the memory barriers required to provide the expected memory visibility semantics. When using ...

Read more here: » Memory barrier: Encyclopedia II - Memory barrier - Threaded programming and memory visibility

Aspect can refer to: Aspect (computer science) is a feature that is linked to many parts of a program, but which is not necessarily the primary function of the program. Grammatical aspect is a grammatical feature having to do with the internal temporal flow of an event. Astrological aspect is the relative angle between two heavenly bodies. Aspect (geography) refers to the direction to which a mountain slope faces. Aspect was also the name of: Alain Aspect, the French p ...

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A conditional branch is a basic logical structure. It resembles a fork in the road; there are at least two paths that may be taken and one must be chosen. This is a common method in computer programming. If a certain condition exists (e.g., the hard disk drive is in use), then the application will perform one action (in this case, it might wait), whereas if this condition does not exist the application will perform another ...

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Concurrent programming languages are programming languages that use language constructs for concurrency. These constructs may involve multi-threading, support for distributed computing, message passing, shared resources (including shared memory) or futures (known also as promises). In some languages communication between concurrent parts of an application is hidden from the programmer (e.g., by using futures), while in others it must be handled explicitly. Explicit communication can be divided into two classes: ... Including:

• Concurrent programming language - Languages where concurrency is important

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Communication is the process of exchanging information, usually via a common protocol. "Communication studies" is the academic discipline focused on communication forms, processes and meanings, including speech, interpersonal and organizational communication. "Mass communication" is a more specialized academic discipline focused on the institutions, practice and effects of journalism, broadcasting, advertising, public relations and related mediated communication directed at a large, undifferentiated or segmented audience. Including:

• Communication - Forms and components of human communication
• Communication - Communication technology
• Communication - Communication barriers
• Communication - Examples of communication

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The traditional approach to multi-threaded programming is to use locks to synchronize access to shared resources. Synchronization primitives such as mutexes, semaphores, and critical sections are all mechanisms by which a programmer can ensure that certain sections of code do not execute concurrently if doing so would corrupt shared memory structures. If one thread attempts to acquire a lock that is already held by an ...

Read more here: » Non-blocking synchronization: Encyclopedia II - Non-blocking synchronization - Motivation

The Join Java extension introduces three new language constucts: Join methods Asynchronous methods Order class modifiers for determining the order that patterns are matched Concurrency expression in most popular programming languages is still quite low level and based on constructs such as semaphores and monitors, that have not changed in twenty years. Libraries that are emerging (such as the Java concurrency library JSR-166) show that programmers demand that higher-level concurrency semantics be ...

Read more here: » Join Java: Encyclopedia II - Join Java - Language characteristics

In databases, locks can be used as a means of ensuring transaction synchronisity. i.e. when making transaction processing concurrent (interleaving transactions), using 2-phased locks ensures that the concurrent execution of the transaction turns out equivalent to some serial ordering of the transaction. 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 synchronisity while avoiding deadlocks involves the ...

Read more here: » Lock computer science: Encyclopedia II - Lock computer science - Database locks

Generally, locks are advisory locks, where each thread cooperates by acquiring the lock before accessing the corresponding data. Some systems also implement mandatory locks, where attempting unauthorized access to a locked resource will force an exception in the entity attempting to make the access. A semaphore is the simplest type of lock. No distinction is made between shared (read only) or exclusive (read and write) modes. Other schemes provide for a shared mode, where several threads can acquire a shared lock for read-only access to the data. Other modes such as shared, exclusive, intend-to-exclude and ...

Read more here: » Lock computer science: Encyclopedia II - Lock computer science - Types