Parallel.ForEach vs. Foreach: When Should You Use Which?

How Parallel.ForEach Differs from Foreach

Foreach loops and Parallel.ForEach are both used to iterate through collections, but they operate in noticeably different ways.

Foreach Loop

• Executes iterations sequentially, one after the other.
• Utilizes a single thread for execution.
• Excels in handling quick processes with minimal overhead.

Parallel.ForEach

• Enables parallel execution of iterations, utilizing multiple threads.
• Accelerates slower processes by leveraging concurrency.
• Introduces threading overhead, potentially slowing down the execution of quick processes.

Example Conversion

The provided example, which reads lines from a file and iterates through them using a foreach loop, can be rewritten with Parallel.ForEach as follows:

string[] lines = File.ReadAllLines(txtProxyListPath.Text);
List<string> list_lines = new List<string>(lines);

Parallel.ForEach(list_lines, (line) =>
{
    // Insert your line-specific operations here
});

In this conversion:

• The Parallel.ForEach method is used to distribute the iteration over multiple threads.
• The line variable within the lambda function represents each line in the collection.
• The specific operations that should be performed on each line are now enclosed within the lambda function.

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