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This article mainly introduces the Linq internal implementation principle is how, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let Xiaobian take you to understand.

Internal execution principle of Linq

LINQ (Language Integrated Query) is the leader in Visual Studio 2008. With the help of LINQ technology, we can use a syntax similar to SQL to query any form of data. So far, the data sources supported by LINQ are SQL Server, XML, and data collections in memory. Developers can also use the extension framework they provide to add more data sources, such as MySQL, Amazon, and even Google Desktop.

Generally speaking, an important feature of this kind of query statement is that it can be executed in parallel. Although parallelism can cause problems in some cases, this is very rare. This naturally leads to PLINQ, a parallel processing LINQ class library.

PLINQ, formerly known as Parallel LINQ, supports XML and in-memory data collections. A query statement executed on a remote server, such as LINQ to SQL, obviously cannot do this.

Converting a LINQ statement to an PLINQ statement is extremely simple-- you only need to add .AsParian () to the data source specified by the From clause in the query statement. Then the Where, OrderBy, and Select clauses are automatically changed to call this parallel version of LINQ.

According to MSDN Magazine, PLINQ can be executed in three ways. * Pipeline processing: one thread is used to read the data source, while the other thread is used to process the query statement, the two are synchronized-although this single consumer thread may not be so easy to synchronize with multiple production threads. However, if load balancing can be carefully configured, the memory footprint will still be greatly reduced.

The second mode, called "stop and go", is used to deal with situations where the result set needs to be returned at once (such as calling ToList, ToArray, or sorting the results). In this mode, each process is completed in turn and the results are uniformly returned to the consumer thread. This mode will outperform the * modes in performance because it saves the overhead of keeping threads synchronized.

* * one method is called "inverted enumeration". This method does not require the implementation to collect all the output and then process it in a single thread, but instead passes the final called function to each thread through the ForAll extension. This is by far the fastest processing mode, but it requires that the functions passed to ForAll are thread-safe and * does not contain any mutexes such as lock.

If any thread in PLINQ throws an exception, all other threads will be terminated. If multiple exceptions are thrown, they will be combined into an exception of type MultipleFailuresException, but the call stack for each exception will still be retained.

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