Advanced Data Parallelism

Previously, we used lock and Monitor to protect shared resources and Parallel.ForEach to speed up CPU-bound loops. However, these older approaches have limitations:

• Parallel.ForEach blocks the calling thread, which makes it poor for I/O operations like calling APIs.

• Manual locking is error-prone and can create bottlenecks.

• Standard collections like List and Dictionary are not thread-safe.

Modern .NET provides specialized tools to handle these scenarios efficiently without blocking threads or writing complex lock logic.

Async parallel loops (Parallel.ForEachAsync)

Introduced in modern .NET, Parallel.ForEachAsync is the asynchronous counterpart to Parallel.ForEach. It is designed specifically for I/O-bound workloads, such as downloading files, calling web APIs, or writing to databases.

Unlike Task.WhenAll which launches all tasks immediately, Parallel.ForEachAsync enforces a concurrency limit to control the number of simultaneous operations. This prevents flooding a server or running out of network sockets.