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Illustration of the dining philosophers problem. Each philosopher has a bowl of spaghetti and can reach two of the forks. In computer science, the dining philosophers problem is an example problem often used in concurrent algorithm design to illustrate synchronization issues and techniques for resolving them.
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 ...
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:
There are several possible solutions, but all solutions require a mutex, which ensures that only one of the participants can change state at once.The barber must acquire the room status mutex before checking for customers and release it when they begin either to sleep or cut hair; a customer must acquire it before entering the shop and release it once they are sitting in a waiting room or ...
The original semaphore bounded buffer solution was written in ALGOL style. The buffer can store N portions or elements. The "number of queueing portions" semaphore counts the filled locations in the buffer, the "number of empty positions" semaphore counts the empty locations in the buffer and the semaphore "buffer manipulation" works as mutex for the buffer put and get operations.
The very last writer must release the readtry semaphore, thus opening the gate for readers to try reading. No reader can engage in the entry section if the readtry semaphore has been set by a writer previously. The reader must wait for the last writer to unlock the resource and readtry semaphores.
To enter a critical section, a thread must obtain a semaphore, which it releases on leaving the section. Other threads are prevented from entering the critical section at the same time as the original thread, but are free to gain control of the CPU and execute other code, including other critical sections that are protected by different semaphores.
Sample Chapter: "Gotcha #67: Failure to Employ Resource Acquisition Is Initialization" by Stephen C. Dewhurst; Interview: "A Conversation with Bjarne Stroustrup" by Bill Venners; Article: "The Law of The Big Two" by Bjorn Karlsson and Matthew Wilson; Article: "Implementing the 'Resource Acquisition is Initialization' Idiom" by Danny Kalev