(n.) A data type for controlling concurrency. A semaphore can be initialised to any non negative integer value. After that, only two operations may be applied to it: "signal" which increments the semaphore's value by one, and "wait" which blocks its caller until the semaphore's value is greater than zero, then decrements the semaphore. The value of a semaphore typically represents the amount of some resource that is currently available, while waiting on a semaphore forces processes to block until some of that resource can be claimed. A binary semaphore is one that can only take on the values 0 and 1.
In Win32, a synchronization object that maintains a count between zero and a specified maximum value. A semaphore's state is signaled when its count is greater than zero and nonsignaled when its count is zero. The semaphore object is useful in controlling a shared resource that can support a limited number of users. It acts like a gate that counts the threads as they enter and exit a controlled area and that limits the number of threads sharing the resource to a specified maximum number. More generally, a flag variable used to govern concurrent processes that share system resources.
(1) A variable that is used to enforce mutual exclusion. (2) In the Windows operating system, a synchronization kernel object used to control the number of threads that simultaneously use a shared resource. See kernel object, critical section, event object.
A Kernel object used to synchronise co-operating threads in Symbian OS. Access to the semaphore is through an RSemaphore handle. See also: request semaphore
A synchronization kernel object used for counting resources. A semaphore offers a thread the ability to query the number of resources available. If one or more resources are available, the count of available resources is decremented. See critical section, kernel object, mutex, event.
A synchronization object used for interprocess communication. A semaphore maintains a count between zero and a maximum value. A semaphore is in a signaled state when its count is positive, and in a nonsignaled state when its count is zero. Back
A means of signalling by holding a flag in each hand and moving the arms to designated positions denoting letters of the alphabet.
A group of bits associated with data structures that act as a flag to all processors to synchronize the threads of a multiple-thread process. See also synchronization.
a counter which can be incremented and decremented
a device to enable cooperation among threads so that one thread doesn't try to access something in a way that could damage another thread's use of that same thing
a flag or label which is stored in an addressable location in memory for controlling access to certain regions of the memory or other addressable resources
a flag shared among workstations (each user's computer) or among processes on the same workstation
a flag used for communication between threads
a flag used for synchronizing processes
a flag used to check whether a resource is currently being used by another thread or process
a flag which can have a more general value than just true or false
a general mechanism for controlling access to resources
a hardware or software flag, residing in a shared memory location, that indicates the accessibility of a shared resource
a kernel data structure shared by two or more processes that controls metered access to the shared resource
an integer counting variable and is used to solve problems where there is competition between processes
an integer number (initialized to a positive value), together with a set of function calls to count up() up() and down()
an integer with a difference
an interprocess synchronization object that maintains a count between zero and some maximum value
a old locking technique where only a specified number of threads can obtain the lock at one time
a primitive for process synchronization
a protected variable (or abstract data type ) and constitutes the classic method for restricting access to shared resources (e
a protected variable (or abstract data type) that can be accessed only by certain operations for testing and incrementing the value of the variable
a software flag that ensures a server completes certain tasks before it can begin another
a special flag that is shared between two tasks
a synchronization function that is used to allow multiple jobs or threads to serialize their access to shared data
a synchronization mechanism that starts out initialized to some positive value
a synchronization primitive with an unsigned value
a system-level flag, or variable, used by Windows processes for coordination purposes
a system to send messages that uses flags, lights, or mechanical arms to encode the message
a token that's used in a multi-threaded operating system to coordinate access, by competing threads, to "protected" resources or operations
a type of Interprocess communication resource used for synchronization and mutual exclusion between any two asynchronous processes
a way to protect a resource
A token passed between two or more devices and used for sharing a common resource.
In computer science: a method for restricting access to shared resources in a multithreaded environment invented by Dijkstra. Operations on semaphores can be either test or increment. A semaphore is free if its value is greater than or equal to 1. It is locked if its value is 0.
A software construct used for synchronization and mutual exclusion.
An integer counter and an associated thread-wait queue. When initialized, the semaphore counter receives a user-defined positive or null value.
A special type of variable used to synchronize tasks, all of which share the semaphore. In the simplest case, when a task reaches its synchronization point, it checks the semaphore. If the semaphore is on, the task must wait until it is off. When the semaphore is off, the task turns it on and continues to execute.
A signal indicator used to control access to system resources. For example, in a multiuser application, it is a flag that prevents simultaneous access to a file.
A data type for controlling concurrency. A semaphore is initialized to an integer value. Two operations may be applied to it: signal increments the semaphore's value by one, and wait blocks its caller until the semaphore's value is greater than zero, then decrements the semaphore. A binary semaphore is one that can only take on the values 0 and 1. Any other synchronization primitive can be built in terms of semaphores.
A system of signaling by means of two flags held in various positions.
A data object that represents the right to use a limited resource, used for synchronization and communication between asynchronous processes. A semaphore contains a count that represents the quantity of available resource (typically 1). The operation (mnemonic: de lete) decrements the count and, if the count goes negative, causes the caller to wait (see psema(D3X) , cpsema(D3X) ). The operation (mnemonic: re ive) increments the count and releases any waiting process (see vsema(D3X) , cvsema(D3X) ). See also lock.
A signal used to govern access to shared system resources.
The semaphore or optical telegraph is an apparatus for conveying information by means of visual signals, with towers with pivoting blades or paddles, shutters, in a matrix, or hand-held flags etc. Information is encoded by the position of the mechanical elements; it is read when the blade or flag is in a fixed position. In modern usage it refers to a system of signaling using two handheld flags.
