Anomalies in parallel algorithms refer to situations where the parallel execution of an algorithm results in unexpected or incorrect behavior.
These anomalies can arise due to a variety of factors, including communication overheads, synchronization issues, and load imbalances. Here are some common anomalies in parallel algorithms:
1. Deadlocks: A deadlock occurs when two or more processes are waiting for each other to release a shared resource or communicate a message, resulting in a state of mutual waiting that prevents any further progress.
2. Race conditions: A race condition occurs when two or more processes are accessing or modifying a shared resource, and the order of their accesses or modifications is not deterministic. This can result in unexpected or incorrect behavior.
3. Load imbalance: Load imbalance occurs when the workload is not evenly distributed among the available processors, resulting in some processors finishing their work much faster than others. This can lead to the underutilization of some processors and the overloading of others, reducing the overall performance of the system.
4. False sharing: False sharing occurs when two or more processors access different variables that happen to reside in the same cache line. This can result in frequent cache invalidations and updates, leading to a significant decrease in performance.
5. Communication overheads: Communication overheads occur when data needs to be transmitted between processors or when synchronization mechanisms are used to ensure consistency. These overheads can result in reduced performance if the communication and synchronization mechanisms are not carefully designed.
To avoid these anomalies, it is important to carefully design parallel algorithms that take into account the characteristics of the underlying hardware and the communication and synchronization mechanisms used. This may involve choosing appropriate data structures, optimizing communication patterns, and load-balancing techniques to ensure that the workload is evenly distributed among the available processors.