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Peterson's Algorithm
Peterson's algorithm (or Peterson's solution) is a concurrent programming algorithm for mutual exclusion that allows two or more processes to share a single-use resource without conflict, using only shared memory for communication. It was formulated by Gary L. Peterson in 1981.G. L. Peterson: "Myths About the Mutual Exclusion Problem", ''Information Processing Letters'' 12(3) 1981, 115–116 While Peterson's original formulation worked with only two processes, the algorithm can be generalized for more than two.As discussed in ''Operating Systems Review'', January 1990 ("Proof of a Mutual Exclusion Algorithm", M Hofri). The algorithm The algorithm uses two variables: flag and turn. A flag /code> value of true indicates that the process n wants to enter the critical section. Entrance to the critical section is granted for process P0 if P1 does not want to enter its critical section and if P1 has given priority to P0 by setting turn to 0. The algorithm satisfies the three essenti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Concurrent Programming
Concurrent means happening at the same time. Concurrency, concurrent, or concurrence may refer to: Law * Concurrence, in jurisprudence, the need to prove both ''actus reus'' and ''mens rea'' * Concurring opinion (also called a "concurrence"), a legal opinion which supports the conclusion, though not always the reasoning, of the majority. * Concurrent estate, a concept in property law * Concurrent resolution, a legislative measure passed by both chambers of the United States Congress * Concurrent sentences, in criminal law, periods of imprisonment that are served simultaneously Computing * Concurrency (computer science), the property of program, algorithm, or problem decomposition into order-independent or partially-ordered units * Concurrent computing, the overlapping execution of multiple interacting computational tasks * Concurrence (quantum computing), a measure used in quantum information theory * Concurrent Computer Corporation, an American computer systems manufacturer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Symmetric Multiprocessing
Symmetric multiprocessing or shared-memory multiprocessing (SMP) involves a multiprocessor computer hardware and software architecture where two or more identical processors are connected to a single, shared main memory, have full access to all input and output devices, and are controlled by a single operating system instance that treats all processors equally, reserving none for special purposes. Most multiprocessor systems today use an SMP architecture. In the case of multi-core processors, the SMP architecture applies to the cores, treating them as separate processors. Professor John D. Kubiatowicz considers traditionally SMP systems to contain processors without caches. Culler and Pal-Singh in their 1998 book "Parallel Computer Architecture: A Hardware/Software Approach" mention: "The term SMP is widely used but causes a bit of confusion. ..The more precise description of what is intended by SMP is a shared memory multiprocessor where the cost of accessing a memory location ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Semaphore (programming)
In computer science, a semaphore is a variable or abstract data type used to control access to a common resource by multiple threads and avoid critical section problems in a concurrent system such as a multitasking operating system. Semaphores are a type of synchronization primitive. A trivial semaphore is a plain variable that is changed (for example, incremented or decremented, or toggled) depending on programmer-defined conditions. A useful way to think of a semaphore as used in a real-world system is as a record of how many units of a particular resource are available, coupled with operations to adjust that record ''safely'' (i.e., to avoid race conditions) as units are acquired or become free, and, if necessary, wait until a unit of the resource becomes available. Semaphores are a useful tool in the prevention of race conditions; however, their use is not a guarantee that a program is free from these problems. Semaphores which allow an arbitrary resource count are calle ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Szymański's Algorithm
Szymański's Mutual Exclusion Algorithm is a mutual exclusion algorithm devised by computer scientist Dr. Bolesław Szymański, which has many favorable properties including linear wait, and which extension solved the open problem posted by Leslie Lamport whether there is an algorithm with a constant number of communication bits per process that satisfies every reasonable fairness and failure-tolerance requirement that Lamport conceived of (Lamport's solution used n factorial communication variables vs. Szymański's 5). The algorithm The algorithm is modeled on a waiting room with an entry and exit doorway. Initially the entry door is open and the exit door is closed. All processes which request entry into the critical section at roughly the same time enter the waiting room; the last of them closes the entry door and opens the exit door. The processes then enter the critical section one by one (or in larger groups if the critical section permits this). The last process to leave ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lamport's Bakery Algorithm
Lamport's bakery algorithm is a computer algorithm devised by computer scientist Leslie Lamport, as part of his long study of the formal correctness of concurrent systems, which is intended to improve the safety in the usage of shared resources among multiple threads by means of mutual exclusion. In computer science, it is common for multiple threads to simultaneously access the same resources. Data corruption can occur if two or more threads try to write into the same memory location, or if one thread reads a memory location before another has finished writing into it. Lamport's bakery algorithm is one of many mutual exclusion algorithms designed to prevent concurrent threads entering critical sections of code concurrently to eliminate the risk of data corruption. Algorithm Analogy Lamport envisioned a bakery with a numbering machine at its entrance so each customer is given a unique number. Numbers increase by one as customers enter the store. A global counter display ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eisenberg & McGuire Algorithm
The Eisenberg & McGuire algorithm is an algorithm for solving the critical sections problem, a general version of the dining philosophers problem. It was described in 1972 by Murray A. Eisenberg and Michael R. McGuire. Algorithm All the ''n''-processes share the following variables: enum pstate = ; pstate flags int turn; The variable turn is set arbitrarily to a number between 0 and ''n''−1 at the start of the algorithm. The flags variable for each process is set to WAITING whenever it intends to enter the critical section. flags takes either IDLE or WAITING or ACTIVE. Initially the flags variable for each process is initialized to IDLE. repeat until ((index >= n) && ((turn = i) , , (flagsurn= IDLE))); /* Start of CRITICAL SECTION */ /* claim the turn and proceed */ turn := i; /* Critical Section Code of the Process */ /* End of CRITICAL SECTION */ /* find a process which is not IDLE */ /* (if there are no others, we will find ourselves) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dekker's Algorithm
Dekker's algorithm is the first known correct solution to the mutual exclusion problem in concurrent programming where processes only communicate via shared memory. The solution is attributed to Dutch mathematician Th. J. Dekker by Edsger W. Dijkstra in an unpublished paper on sequential process descriptions and his manuscript on cooperating sequential processes. It allows two threads to share a single-use resource without conflict, using only shared memory for communication. It avoids the strict alternation of a naïve turn-taking algorithm, and was one of the first mutual exclusion algorithms to be invented. Overview If two processes attempt to enter a critical section at the same time, the algorithm will allow only one process in, based on whose it is. If one process is already in the critical section, the other process will busy wait for the first process to exit. This is done by the use of two flags, and , which indicate an intention to enter the critical section on the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MIPS Architecture
MIPS (Microprocessor without Interlocked Pipelined Stages) is a family of reduced instruction set computer (RISC) instruction set architectures (ISA)Price, Charles (September 1995). ''MIPS IV Instruction Set'' (Revision 3.2), MIPS Technologies, Inc. developed by MIPS Computer Systems, now MIPS Technologies, based in the United States. There are multiple versions of MIPS: including MIPS I, II, III, IV, and V; as well as five releases of MIPS32/64 (for 32- and 64-bit implementations, respectively). The early MIPS architectures were 32-bit; 64-bit versions were developed later. As of April 2017, the current version of MIPS is MIPS32/64 Release 6. MIPS32/64 primarily differs from MIPS I–V by defining the privileged kernel mode System Control Coprocessor in addition to the user mode architecture. The MIPS architecture has several optional extensions. MIPS-3D which is a simple set of floating-point SIMD instructions dedicated to common 3D tasks, MDMX (MaDMaX) which is a more exten ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DEC Alpha
Alpha (original name Alpha AXP) is a 64-bit reduced instruction set computer (RISC) instruction set architecture (ISA) developed by Digital Equipment Corporation (DEC). Alpha was designed to replace 32-bit VAX complex instruction set computers (CISC) and to be a highly competitive RISC processor for Unix workstations and similar markets. Alpha is implemented in a series of microprocessors originally developed and fabricated by DEC. These microprocessors are most prominently used in a variety of DEC workstations and servers, which eventually formed the basis for almost all of their mid-to-upper-scale lineup. Several third-party vendors also produced Alpha systems, including PC form factor motherboards. Operating systems that support Alpha included OpenVMS (formerly named OpenVMS AXP), Tru64 UNIX (formerly named DEC OSF/1 AXP and Digital UNIX), Windows NT (discontinued after NT 4.0; and prerelease Windows 2000 RC2), Linux ( Debian, SUSE, Gentoo and Red Hat), BSD UNIX ( Ne ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Load-link/store-conditional
In computer science, load-linked/store-conditional (LL/SC), sometimes known as load-reserved/store-conditional (LR/SC), are a pair of instructions used in multithreading to achieve synchronization. Load-link returns the current value of a memory location, while a subsequent store-conditional to the same memory location will store a new value only if no updates have occurred to that location since the load-link. Together, this implements a lock-free atomic read-modify-write operation. "Load-linked" is also known as load-link, load-reserved, and load-locked. LL/SC was originally proposed by Jensen, Hagensen, and Broughton for the S-1 AAP multiprocessor at Lawrence Livermore National Laboratory. Comparison of LL/SC and compare-and-swap If any updates have occurred, the store-conditional is guaranteed to fail, even if the value read by the load-link has since been restored. As such, an LL/SC pair is stronger than a read followed by a compare-and-swap (CAS), which will not detect up ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atomic Operation
In concurrent programming, an operation (or set of operations) is linearizable if it consists of an ordered list of invocation and response events (event), that may be extended by adding response events such that: # The extended list can be re-expressed as a sequential history (is 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 at the same time. Because multiple processes are accessing a single object, there may arise a situation 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 operations overlap on a shared object, each operation appears to take place i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xbox 360
The Xbox 360 is a home video game console developed by Microsoft. As the successor to the original Xbox, it is the second console in the Xbox series. It competed with Sony's PlayStation 3 and Nintendo's Wii as part of the seventh generation of video game consoles. It was officially unveiled on MTV on May 12, 2005, with detailed launch and game information announced later that month at the 2005 Electronic Entertainment Expo (E3). The Xbox 360 features an online service, Xbox Live, which was expanded from its previous iteration on the original Xbox and received regular updates during the console's lifetime. Available in free and subscription-based varieties, Xbox Live allows users to: play games online; download games (through Xbox Live Arcade) and game demos; purchase and stream music, television programs, and films through the Xbox Music and Xbox Video portals; and access third-party content services through media streaming applications. In addition to online multimedia ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
