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A vector clock of a system of N processes is an array/vector of N logical clocks, one clock per process; a local "largest possible values" copy of the global clock-array is kept in each process. Denote V C i {\displaystyle VC_{i}} as the vector clock maintained by process i {\displaystyle i} , the clock updates proceed as follows: [ 1 ]
The Lamport timestamp algorithm is a simple logical clock algorithm used to determine the order of events in a distributed computer system.As different nodes or processes will typically not be perfectly synchronized, this algorithm is used to provide a partial ordering of events with minimal overhead, and conceptually provide a starting point for the more advanced vector clock method.
Clock synchronization provides all nodes with an equivalent time concept. Each node measures the difference between the a priori known expected and the observed arrival time of a correct message to learn about the difference between the sender’s clock and the receiver’s clock. A fault-tolerant average algorithm needs this information to ...
In logical clock systems each process has two data structures: logical local time and logical global time. Logical local time is used by the process to mark its own events, and logical global time is the local information about global time.
Time-triggered systems can be viewed as a subset of a more general event-triggered (ET) system architecture (see event-driven programming).. Implementation of an ET system will typically involve use of multiple interrupts, each associated with specific periodic events (such as timer overflows) or aperiodic events (such as the arrival of messages over a communication bus at random points in time).
This is usually stored in a data structure called a process control block (PCB) or switchframe. The PCB might be stored on a per-process stack in kernel memory (as opposed to the user-mode call stack ), or there may be some specific operating system-defined data structure for this information.
Clock synchronization is a topic in computer science and engineering that aims to coordinate otherwise independent clocks. Even when initially set accurately, real clocks will differ after some amount of time due to clock drift , caused by clocks counting time at slightly different rates.
A matrix clock is a mechanism for capturing chronological and causal relationships in a distributed system. Matrix clocks are a generalization of the notion of vector clocks . [ 1 ] A matrix clock maintains a vector of the vector clocks for each communicating host.