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Raymond's Algorithm
Raymond's Algorithm is a lock based algorithm for mutual exclusion on a distributed system. It imposes a logical structure (a K-ary tree) on distributed resources. As defined, each node has only a single parent, to which all requests to attain the token are made. Algorithm Nodal properties # Each node has only one parent to whom received requests are forwarded # Each node maintains a FIFO queue of requests each time that it sees the token; # If any node is forwarding privilege to other node and has non-empty queue then it forwards a request message along Algorithm # If a node ''i'' (not holding the token) wishes to receive the token in order to enter into its critical section, it sends a request to its parent, node ''j''. #* If node ''j'' FIFO is empty, node ''j'' shifts ''i'' into its FIFO queue; ''j'' then issues a request to its parent, ''k'', that it desires the token #* If node ''j'' FIFO queue is ''not'' empty, it simply shifts ''i'' into the queue # When node ''k'' h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mutual Exclusion
In computer science, mutual exclusion is a property of concurrency control, which is instituted for the purpose of preventing race conditions. It is the requirement that one thread of execution never enters a critical section while a concurrent thread of execution is already accessing said critical section, which refers to an interval of time during which a thread of execution accesses a shared resource or shared memory. The shared resource is a data object, which two or more concurrent threads are trying to modify (where two concurrent read operations are permitted but, no two concurrent write operations or one read and one write are permitted, since it leads to data inconsistency). Mutual exclusion algorithm ensures that if a process is already performing write operation on a data object ritical sectionno other process/thread is allowed to access/modify the same object until the first process has finished writing upon the data object ritical sectionand released the object ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Distributed System
A distributed system is a system whose components are located on different networked computers, which communicate and coordinate their actions by passing messages to one another from any system. Distributed computing is a field of computer science that studies distributed systems. The components of a distributed system interact with one another in order to achieve a common goal. Three significant challenges of distributed systems are: maintaining concurrency of components, overcoming the lack of a global clock, and managing the independent failure of components. When a component of one system fails, the entire system does not fail. Examples of distributed systems vary from SOA-based systems to massively multiplayer online games to peer-to-peer applications. A computer program that runs within a distributed system is called a distributed program, and ''distributed programming'' is the process of writing such programs. There are many different types of implementations for t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
K-ary Tree
In graph theory, an ''m''-ary tree (also known as ''n''-ary, ''k''-ary or ''k''-way tree) is a rooted tree in which each node has no more than ''m'' children. A binary tree is the special case where ''m'' = 2, and a ternary tree is another case with ''m'' = 3 that limits its children to three. Types of ''m''-ary trees * A full ''m''-ary tree is an ''m''-ary tree where within each level every node has either 0 or ''m'' children. * A complete ''m''-ary tree is an ''m''-ary tree which is maximally space efficient. It must be completely filled on every level except for the last level. However, if the last level is not complete, then all nodes of the tree must be "as far left as possible". * A perfect ''m''-ary tree is a full ''m''-ary tree in which all leaf nodes are at the same depth. Properties of ''m''-ary trees * For an ''m''-ary tree with height ''h'', the upper bound for the maximum number of leaves is m^h. * The height ''h ''of an ''m''-ary tree does not include the ro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
FIFO (computing And Electronics)
Representation of a FIFO queue In computing and in systems theory, FIFO is an acronym for first in, first out (the first in is the first out), a method for organizing the manipulation of a data structure (often, specifically a data buffer) where the oldest (first) entry, or "head" of the queue, is processed first. Such processing is analogous to servicing people in a queue area on a first-come, first-served (FCFS) basis, i.e. in the same sequence in which they arrive at the queue's tail. FCFS is also the jargon term for the FIFO operating system scheduling algorithm, which gives every process central processing unit (CPU) time in the order in which it is demanded. FIFO's opposite is LIFO, last-in-first-out, where the youngest entry or "top of the stack" is processed first. A priority queue is neither FIFO or LIFO but may adopt similar behaviour temporarily or by default. Queueing theory encompasses these methods for processing data structures, as well as interactions b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Critical Section
In concurrent programming, concurrent accesses to shared resources can lead to unexpected or erroneous behavior, so parts of the program where the shared resource is accessed need to be protected in ways that avoid the concurrent access. One way to do so is known as a critical section or critical region. This protected section cannot be entered by more than one process or thread at a time; others are suspended until the first leaves the critical section. Typically, the critical section accesses a shared resource, such as a data structure, a peripheral device, or a network connection, that would not operate correctly in the context of multiple concurrent accesses. Need for critical sections Different codes or processes may consist of the same variable or other resources that need to be read or written but whose results depend on the order in which the actions occur. For example, if a variable is to be read by process A, and process B has to write to the same variabl ... [...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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Maekawa's Algorithm
Maekawa's algorithm is an algorithm for mutual exclusion on a distributed system. The basis of this algorithm is a quorum-like approach where any one site needs only to seek permissions from a subset of other sites. Algorithm Terminology * A ''site'' is any computing device which runs the Maekawa's algorithm * For any one request of entering the critical section: ** The ''requesting site'' is the site which is requesting to enter the critical section. ** The ''receiving site'' is every other site which is receiving the request from the requesting site. * ''ts'' refers to the local time stamp of the system according to its logical clock Algorithm Requesting site: * A requesting site P_i sends a message \text(ts, i) to all sites in its quorum set R_i. Receiving site: * Upon reception of a \text(ts, i) message, the receiving site P_j will: ** If site P_j does not have an outstanding \text message (that is, a \text message that has not been released), then site P_j sends a \text(j) m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
