Event (synchronization primitive)
Encyclopedia
In computer science
, an event (also called event semaphore) is a type of synchronization
mechanism that is used to indicate to waiting processes when a particular condition has become true.
An event is an abstract data type
with a boolean state and the following operations:
Different implementations of events may provide different subsets of these possible operations; for example, the implementation provided by Microsoft Windows
provides the operations wait (WaitForObject and related functions), set (SetEvent), and clear (ResetEvent). An option that may be specified during creation of the event object changes the behaviour of SetEvent so that only a single process is released and the state is automatically returned to false after that process is released.
Events are similar in principle to the condition variables used in monitors
, although the precise mechanism of use is somewhat different.
Computer science
Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...
, an event (also called event semaphore) is a type of synchronization
Synchronization (computer science)
In computer science, synchronization refers to one of two distinct but related concepts: synchronization of processes, and synchronization of data. Process synchronization refers to the idea that multiple processes are to join up or handshake at a certain point, so as to reach an agreement or...
mechanism that is used to indicate to waiting processes when a particular condition has become true.
An event is an abstract data type
Abstract data type
In computing, an abstract data type is a mathematical model for a certain class of data structures that have similar behavior; or for certain data types of one or more programming languages that have similar semantics...
with a boolean state and the following operations:
- wait - when executed, causes the executing process to suspend until the event's state is set to true. If the state is already set to true has no effect.
- set - sets the event's state to true, release all waiting processes.
- clear - sets the event's state to false.
Different implementations of events may provide different subsets of these possible operations; for example, the implementation provided by Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
provides the operations wait (WaitForObject and related functions), set (SetEvent), and clear (ResetEvent). An option that may be specified during creation of the event object changes the behaviour of SetEvent so that only a single process is released and the state is automatically returned to false after that process is released.
Events are similar in principle to the condition variables used in monitors
Monitor (synchronization)
In concurrent programming, a monitor is an object or module intended to be used safely by more than one thread. The defining characteristic of a monitor is that its methods are executed with mutual exclusion. That is, at each point in time, at most one thread may be executing any of its methods...
, although the precise mechanism of use is somewhat different.
External links
- Event Objects, Microsoft Developer Network
- Thread Synchronization Mechanisms in Python