Consumer code from chapter 3: One slot is unavailable because there always has to be a gap between the producer and the consumer.
The beta release includes the Concurrency Runtime, parallel libraries, and development tools aimed at addressing several common problems preventing developers from unlocking the performance potential inherent to multicore hardware. Notably, this includes ensuring that developers can identify and take advantage of opportunities for concurrency in their code, productively manage shared state and its side effects, and not having to worry about building low-overhead concurrency infrastructure that is scalable at run time on a variety of hardware.
To show you how this works, I will walk through an implementation of a classic concurrency problem: You'll see how the actor-based programming construct of an agent in combination with asynchronous message-passing APIs can be used to provide a correct and easy to understand solution to this problem that doesn't rely directly on threading or synchronization primitives.
The Dining Philosophers For those who aren't familiar with it, the Dining Philosophers problem is intended to illustrate the complexities of managing shared state in a multithreaded environment.
Aug 14, · I have to write a program that solves the producer/consumer problem using shared memory, cicular buffer, mutex's and semaphores. My problem is that while the course teaches us the theory behind these structures I have been given nothing on how to implement these in C. Dec 16, · X and Y and the selected operation are given to the calculator processes. All of the calculator processes must wait the input from the leader process. When they know which is the operation, they give the result to the leader process. I have to implement this part by using semaphores and shared memory (without message queues). The problem is also reffered to as the “bounded buffer problem” as we have a limited size buffer that must be shared by two processes (maybe part of the same program.
At a round table sit five philosophers who alternate between thinking and eating from a large bowl of rice at random intervals. Unfortunately for the philosophers, there are only five chopsticks at the table see Figure 1and before the philosophers can begin eating, they must acquire a pair of chopsticks.
Since the chopsticks are shared between the philosophers, access to the chopsticks must be protected, but if care isn't taken, concurrency problems arise. Most notably, starvation pun intended via deadlock can occur: Figure 1 The Philosophers and Chopsticks The Dining Philosophers problem is typically represented in code by a thread for each philosopher and some form of shared state used to represent each of the chopsticks.
Straightforward solutions to this problem often involve introducing a waiter entity to coordinate access to the chopsticks, introducing lock ordering heuristics, and manually working with threading APIs, critical sections, semaphores, or monitors to manage the state.
Most developers will agree that building correct, nontrivial locking is considered challenging and fragile at best.
As a result, most implementations of the Dining Philosophers problem tend to have implementation details leaked into them. For example, the Philosophers may be aware of the synchronization primitives or of their neighbors' chopsticks. This becomes particularly problematic if you want to generalize the problem to an arbitrary number of philosophers or refocus an implementation on the problem domain—such as what each philosopher does—rather than focusing on the synchronization and threading primitives.
Dining Philosophers really only has two moderately difficult sections: The Asynchronous Agents Library provides an actor-based programming model and asynchronous message passing APIs, and you'll need both of these in the implementation.
In the Asynchronous Agents Library, the agent class models an actor pattern and provides an asynchronous run method. I use an agent for each philosopher and take advantage of the run method to fulfill the requirement of each philosopher running in its own thread.
The second portion of a correct solution involves managing concurrent access to the chopsticks and, in contrast to traditional solutions using semaphores or locks, I'll use the message passing APIs in the Asynchronous Agents Library to move the chopsticks between the philosophers' hands and the table.
As each philosopher transitions between thinking and eating, he picks up the chopsticks and returns them to the table by sending messages.
You'll see that in addition to providing some abstraction on top of threads and shared state, this will also allow the implementation to stay more focused on the domain of the problem than other solutions enable.
A Chopstick class that is relatively self explanatory.
A ChopstickProvider class that will be used to hold the chopsticks on the table and provide them to the philosophers. A Philosopher class that is responsible for thinking and eating and is aware only of its two ChopstickProviders.
A PhilospherState enum that can be thinking or eating. A Table class that contains a set of Philosophers and a set of Chopsticks.
Table is responsible for setting the table by placing a single Chopstick in a ChopstickProvider between each Philosopher. Figure 2shows the relationships between the classes. The purpose of the Chopstick is to simply exist as a chopstick and be able to identify itself.
As a result, the implementation is a simple class that has an identifier member variable, a constructor that initializes the identifier, and a method to return the identifier.segment of memory that they can both read to and write from to communicate with one another.
Nothing more, nothing less. There’s a problem with using shared memory, a rather nasty problem—race conditions. Shared memory is, well, a shared resource. Shared Memory and Semaphores. The producer–consumer problem, particularly in the case of a single producer and single consumer, strongly relates to implementing a FIFO or a channel.
The producer–consumer pattern can provide highly efficient data communication without relying on semaphores, mutexes, or . You have to decide wether you use a semaphore or mutex, then you have to use sem_init instead of pthread_mutex_init and sould set the initial value to 1, as wait_sem decreases the value of the semaphore, if the Value is > 0 else it blocks until the Value gets > 0.
shared memory object, to reinforce that the shared memory object appears in the address space of both the client and the server. The concepts involved in using shared memory . The purpose of this assignment is to give you some "hands-on" experience with concurrent processes, semaphores, and shared memory.
The program is an implementation of the bounded, circular buffer Single Producer/ Single Consumer problem. Implementation. Because all the processes will be updating certain shared variables, the most natural way to write this program is to use shared memory. While Unix processes do not share memory by default, some systems have system calls that do create processes that share memory.
Also, many systems now support threads.