Transactional memory is a multithreaded programming policy that uses transactions similar to databases. Locks can cause issues with concurrency, but advanced locks can solve these problems. The TCC model simplifies parallel software by eliminating synchronization and uses hardware to transmit packets atomically to shared memory.
In software, the transactional memory scheme is a policy for multithreaded programming that uses transactions very similar to those used by a database. When two or more threads try to access the same data at the same time, several undesirable situations can arise where the result of a program depends on the thread’s access order. Usually, order is desired, and in multithreading, locks are the predominant and easiest way to ensure that only a single thread has access to a specific resource at a time.
This approach to transactional memory contains more lock issues in multithreading. A lockout can become permanent if some kind of unexpected error occurs, and lockouts can cause unpredictable problems with concurrency, such as deadlocks or priority inversion. Because locks are very verbose, another problem includes code that ends up spending most of the time between locking, context switching, and unlocking. This is a crucial problem because it can cause your code to spend more time on these actions than on other important operations in the program. Conversely, coarse-grained blocks can cause decreased processing performance and concurrency.
Problems in transactional memory are solved by advanced locks, including “block lock” from C#, read-write locks, write barriers, etc. One of the top priorities with regards to transactional memory is to have no blocks and no unnecessary block processing time. It is usually agreed that a shared data structure is lock-free if mutual exclusion from its operations is not required. Shared, lock-free data structures avoid the problems commonly associated with standard locking techniques when found in highly concurrent systems.
The Transactional Memory Coherence and Consistency (TCC) model is a new model proposed on shared memory. According to the model, atomic transactions are invariably basic units of the following: parallel work, memory consistency, communication, and memory reference consistency. The TCC model also simplifies parallel software by eliminating synchronization that uses standard blocks or semaphores. Through the hardware, TCC also combines each write from each region of transaction occurrence into a packet to transmit the packet atomically to a permanently shared memory state. In addition to streamlined consistency hardware, this means a reduction in low dormancy messages and the complete elimination of some standard consistency protocols is required.
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