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Compare-and-swap
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 (the previous) 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. The atomicity guarantees that the new value is calculated based on up-to-date information; if the value had been updated by another thread in the meantime, the write would fail. The result of the operation must indicate whether it performed the substitution; this can be done either with a simple boolean response (this variant is often called compare-and-set), or by returning the value read from the memory location (''not'' the value written to it), thus "swapping" the read and written values. Overview A compare-and-swap operation is an atomic version of the following pseudocode, where denotes access through a pointer: function cas(p: poin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wait-free
In computer science, an algorithm is called non-blocking if failure or suspension of any thread cannot cause failure or suspension of another thread; for some operations, these algorithms provide a useful alternative to traditional blocking implementations. A non-blocking algorithm is lock-free if there is guaranteed system-wide progress, and wait-free if there is also guaranteed per-thread progress. "Non-blocking" was used as a synonym for "lock-free" in the literature until the introduction of obstruction-freedom in 2003. The word "non-blocking" was traditionally used to describe telecommunications networks that could route a connection through a set of relays "without having to re-arrange existing calls" (see Clos network). Also, if the telephone exchange "is not defective, it can always make the connection" (see nonblocking minimal spanning switch). Motivation The traditional approach to multi-threaded programming is to use locks to synchronize access to shared resour ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atomic (computer Science)
In concurrent programming, an operation (or set of operations) is linearizable if it consists of an ordered list of Execution (computing), invocation and response Event (computing), events, that may be extended by adding response events such that: # The extended list can be re-expressed as a sequential history (is serializability, serializable). # That sequential history is a subset of the original unextended list. Informally, this means that the unmodified list of events is linearizable if and only if its invocations were serializable, but some of the responses of the serial schedule have yet to return. In a concurrent system, processes can access a shared Object (computer science), object at the same time. Because multiple processes are accessing a single object, a situation may arise in which while one process is accessing the object, another process changes its contents. Making a system linearizable is one solution to this problem. In a linearizable system, although operat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lock-free And Wait-free Algorithms
In computer science, an algorithm is called non-blocking if failure or suspension of any thread cannot cause failure or suspension of another thread; for some operations, these algorithms provide a useful alternative to traditional blocking implementations. A non-blocking algorithm is lock-free if there is guaranteed system-wide progress, and wait-free if there is also guaranteed per-thread progress. "Non-blocking" was used as a synonym for "lock-free" in the literature until the introduction of obstruction-freedom in 2003. The word "non-blocking" was traditionally used to describe telecommunications networks that could route a connection through a set of relays "without having to re-arrange existing calls" (see Clos network). Also, if the telephone exchange "is not defective, it can always make the connection" (see nonblocking minimal spanning switch). Motivation The traditional approach to multi-threaded programming is to use locks to synchronize access to shared res ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fetch-and-add
In computer science, the fetch-and-add (FAA) CPU instruction atomically increments the contents of a memory location by a specified value. That is, fetch-and-add performs the following operation: increment the value at address by , where is a memory location and is some value, and return the original value at . in such a way that if this operation is executed by one process in a concurrent system, no other process will ever see an intermediate result. Fetch-and-add can be used to implement concurrency control structures such as mutex locks and semaphores. Overview The motivation for having an atomic fetch-and-add is that operations that appear in programming languages as are not safe in a concurrent system, where multiple processes or threads are running concurrently (either in a multi-processor system, or preemptively scheduled onto some single-core systems). The reason is that such an operation is actually implemented as multiple machine instructions: # load in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Test-and-set
In computer science, the test-and-set instruction is an instruction used to write (set) 1 to a memory location and return its old value as a single atomic (i.e., non- interruptible) operation. The caller can then "test" the result to see if the state was changed by the call. If multiple processes may access the same memory location, and if a process is currently performing a test-and-set, no other process may begin another test-and-set until the first process's test-and-set is finished. A central processing unit (CPU) may use a test-and-set instruction offered by another electronic component, such as dual-port RAM; a CPU itself may also offer a test-and-set instruction. A lock Lock(s) or Locked may refer to: Common meanings *Lock and key, a mechanical device used to secure items of importance *Lock (water navigation), a device for boats to transit between different levels of water, as in a canal Arts and entertainme ... can be built using an atomic test-and-set instructio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Futex
In computing, a futex (short for "fast userspace mutex") is a kernel system call that programmers can use to implement basic locking, or as a building block for higher-level locking abstractions such as semaphores and POSIX mutexes or condition variables. A futex consists of a kernel-space ''wait queue'' that is attached to an atomic integer in userspace. Multiple processes or threads operate on the integer entirely in userspace (using atomic operations to avoid interfering with one another), and only resort to the fast but still more expensive system calls to request operations on the wait queue (for example to wake up waiting processes, or to put the current process on the wait queue). A properly programmed futex-based lock will not use system calls except when the lock has contention; since most operations do not require arbitration between processes, this will not happen in most cases. History Hubertus Franke (IBM Thomas J. Watson Research Center), Matthew Kirkwoo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Westmere-EX
Xeon (; ) is a brand of x86 microprocessors designed, manufactured, and marketed by Intel, targeted at the non-consumer workstation, server, and embedded markets. It was introduced in June 1998. Xeon processors are based on the same architecture as regular desktop-grade CPUs, but have advanced features such as support for error correction code (ECC) memory, higher core counts, more PCI Express lanes, support for larger amounts of RAM, larger cache memory and extra provision for enterprise-grade reliability, availability and serviceability (RAS) features responsible for handling hardware exceptions through the Machine Check Architecture (MCA). They are often capable of safely continuing execution where a normal processor cannot due to these extra RAS features, depending on the type and severity of the machine-check exception (MCE). Some also support multi-socket systems with two, four, or eight sockets through use of the Ultra Path Interconnect (UPI) bus, which replaced the ol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ABA Problem
In multithreaded computing, the ABA problem occurs during synchronization, when a location is read twice, has the same value for both reads, and the read value being the same twice is used to conclude that nothing has happened in the interim; however, another thread can execute between the two reads and change the value, do other work, then change the value back, thus fooling the first thread into thinking nothing has changed even though the second thread did work that violates that assumption. The ABA problem occurs when multiple threads (or processes) accessing shared data interleave. Below is a sequence of events that illustrates the ABA problem: # Process P_1 reads value A from some shared memory location, # P_1 is preempted, allowing process P_2 to run, # P_2 writes value B to the shared memory location # P_2 writes value A to the shared memory location # P_2 is preempted, allowing process P_1 to run, # P_1 reads value A from the shared memory location, # P_1 determines t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Science
Computer science is the study of computation, information, and automation. Computer science spans Theoretical computer science, theoretical disciplines (such as algorithms, theory of computation, and information theory) to Applied science, applied disciplines (including the design and implementation of Computer architecture, hardware and Software engineering, software). Algorithms and data structures are central to computer science. The theory of computation concerns abstract models of computation and general classes of computational problem, problems that can be solved using them. The fields of cryptography and computer security involve studying the means for secure communication and preventing security vulnerabilities. Computer graphics (computer science), Computer graphics and computational geometry address the generation of images. Programming language theory considers different ways to describe computational processes, and database theory concerns the management of re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Type I Error
Type I error, or a false positive, is the erroneous rejection of a true null hypothesis in statistical hypothesis testing. A type II error, or a false negative, is the erroneous failure in bringing about appropriate rejection of a false null hypothesis. Type I errors can be thought of as errors of commission, in which the status quo is erroneously rejected in favour of new, misleading information. Type II errors can be thought of as errors of omission, in which a misleading status quo is allowed to remain due to failures in identifying it as such. For example, if the assumption that people are ''innocent until proven guilty'' were taken as a null hypothesis, then proving an innocent person as guilty would constitute a Type I error, while failing to prove a guilty person as guilty would constitute a Type II error. If the null hypothesis were inverted, such that people were by default presumed to be ''guilty until proven innocent'', then proving a guilty person's innocence would ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
System/370
The IBM System/370 (S/370) is a range of IBM mainframe computers announced as the successors to the IBM System/360, System/360 family on June 30, 1970. The series mostly maintains backward compatibility with the S/360, allowing an easy migration path for customers; this, plus improved performance, were the dominant themes of the product announcement. Early 370 systems differed from the 360 largely in their internal circuitry, moving from the Solid Logic Technology hybrid integrated circuits containing separate transistors to more modern monolithic integrated circuits containing multiple transistors per integrated circuit, which IBM referred to as Monolithic System Technology, or MST. The higher density packaging allowed several formerly optional features from the 360 line to be included as standard features of the machines, floating-point support for instance. The 370 also added a small number of new instructions. At the time of its introduction, the development of virtual mem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
