This was once a dreaded paradigm, that only the experts used with extreme caution. Today, concurrency is an integral part of most applications. Naturally, everyone cannot (and should not) reinvent the wheel for implementing a concurrent system. Over the years, some common design patterns have emerged and these are borrowed by most designers. Here are some of the important concurrency patterns.
- Active Object - Decouples method execution from method invocation that reside in their own thread of control. The goal is to introduce concurrency, by using asynchronous method invocation and a scheduler for handling requests.
- Balking - Only execute an action on an object when the object is in a particular state.
- Binding properties - Combining multiple observers to force properties in different objects to be synchronized or coordinated in some way.
- Blockchain - Decentralized way to store data and agree on ways of processing it in a Merkle tree, optionally using digital signature for any individual contributions.
- Compute kernel - The same calculation many times in parallel, differing by integer parameters used with non-branching pointer math into shared arrays, such as GPU-optimized Matrix multiplication or Convolutional neural network.
- Event-based asynchronous - Addresses problems with the asynchronous pattern that occur in multithreaded programs.
- Guarded suspension - Manages operations that require both a lock to be acquired and a precondition to be satisfied before the operation can be executed.
- Join - Join-pattern provides a way to write concurrent, parallel and distributed programs by message passing. Compared to the use of threads and locks, this is a high-level programming model.
- Lock - One thread puts a "lock" on a resource, preventing other threads from accessing or modifying it.
- Messaging design pattern (MDP) - Allows the interchange of information (i.e. messages) between components and applications.
- Monitor object - An object whose methods are subject to mutual exclusion, thus preventing multiple objects from erroneously trying to use it at the same time.
- Reactor - A reactor object provides an asynchronous interface to resources that must be handled synchronously.
- Read-write lock - Allows concurrent read access to an object, but requires exclusive access for write operations.
- Scheduler - Explicitly control when threads may execute single-threaded code.
- Thread pool - A number of threads are created to perform a number of tasks, which are usually organized in a queue. Typically, there are many more tasks than threads. Can be considered a special case of the object pool pattern.
- Thread-specific storage - Static or "global" memory local to a thread.