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This article focuses on "how to use CallContext to cache thread data in C #". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "how to use CallContext to cache thread data".

I. Overview of CallContext

Namespace: System.Runtime.Remoting.Messaging

CallContext is used to provide a set of properties that are passed along with the execution code path, which, to put it bluntly, provides the ability to pass data in a threaded (multithreaded / single-threaded) code execution path.

When a remote method call is made to an object in another AppDomain, the CallContext class generates an instance of LogicalCallContext that propagates with that remote call. Only objects that expose the ILogicalThreadAffinative interface and are stored in CallContext are propagated outside the AppDomain in LogicalCallContext.

CallContext member

SetData: stores the given object and associates it with the specified name.

GetData: retrieves an object with the specified name from CallContext

LogicalSetData: stores the given object in the logical call context and associates it with the specified name. Can be used in multithreaded environment

LogicalGetData: retrieves an object with the specified name from the context of a logical call. Can be used in multithreaded environment

FreeNamedDataSlot: clears the data slot with the specified name. Can be used in multithreaded environment

HostContext property: gets or sets the host context associated with the current thread. Equal to System.Web.HttpContext.Current in Web environment

GetData 、 SetData

It can only be used in a single-threaded environment. If a thread switch occurs, the stored data will be lost.

Can be used in different places in the same thread to pass data

LogicalSetData 、 LogicalGetData

LogicalSetData and LogicalGetData can be used to transfer data in multithreaded environment.

LogicalSetData is just a data slot that stores the current thread and child threads.

LogicalGetData gets the data slot object of the current thread or parent thread and gets a reference to the object

FreeNamedDataSlot clears the current thread. The subtask has been run before and is not affected. It cannot clear the data slot of the subthread.

2. Methods for CallContext not to propagate across threads: GetData, SetData

You can use CallContext to implement a singleton, and by default, CallContext's data is not propagated across threads.

1. It is very useful when dealing with multi-component shared Context. For example, a common EF can store the DBEntity of an instance in it, and it can be instantiated only once at a time, which is easy to manage and does not require multiple instances to access objects.

Public static class DbContextHelper {private static DbContext context = null; private const string SessionKey_DbContext = "Entities"; public static DbContext GetDbContext () {if (CallContext.GetData (SessionKey_DbContext) = = null) {CallContext.SetData (SessionKey_DbContext, new Entities ());} return CallContext.GetData (SessionKey_DbContext) as Entities;}}

2. Class singleton

Void Main () {MyAppContext.Current.FirstName = "a"; Console.Write (MyAppContext.Current.FirstName);} public class MyAppContext {const string contextKey = "MyAppContext:ContextKey"; public string FirstName {get; set;} public static MyAppContext Current {get {if (contextKey) = = null) {CallContext.SetData (contextKey, new MyAppContext ()) } return CallContext.GetData (SessionKey_DbContext) as MyAppContext;}} III. Methods of CallContext cross-thread propagation: ILogicalSetData, LogicalGetData

To allow CallContext to implement cross-thread propagation, you can call CallContext's static method ILogicalSetData, or have the context class implement the ILogicalThreadAffinative interface.

Thread local storage

The thread pool may not release used threads, resulting in the possibility of sharing data between multiple executions (data stored locally by the thread can be reset before each execution).

For (var I = 0; I

{var slot = Thread.GetNamedDataSlot ("test"); if (slot = = null) {Thread.AllocateNamedDataSlot ("test");} if (Thread.GetData (slot) = = null) {Thread.SetData (slot, DateTime.Now.Millisecond);} Console.WriteLine (Thread.CurrentThread.ManagedThreadId + ":" + Thread.GetData (slot);});}

Result

Calling context

The data of each execution is completely isolated and meets our expectations very well. However, if we expect another child thread to be opened during the call, how do we get the child thread to access the data of the parent thread? This requires the use of "logical invocation context".

Console.WriteLine ("Test: CallContext.SetData"); for (var I = 0; I

{if (CallContext.GetData ("test") = = null) {CallContext.SetData ("test", DateTime.Now.Millisecond);} Console.WriteLine (Thread.CurrentThread.ManagedThreadId + ":" + CallContext.GetData ("test"));});}

Result

The data of each execution is completely isolated and meets our expectations very well.

Logical call context

If we expect another child thread to be started during the call, how do we get the child thread to access the data of the parent thread? This requires the use of "logical invocation context".

Note ExecutionContext.SuppressFlow (); and ExecutionContext.RestoreFlow (); they block propagation and reset propagation, respectively, and propagation is allowed by default.

Console.WriteLine ("Test: CallContext.SetData"); Task.Run () = > {CallContext.SetData ("test", "Duan Guangwei"); Console.WriteLine (Thread.CurrentThread.ManagedThreadId + ":" + CallContext.GetData ("test")); Task.Run (() = > {Console.WriteLine (Thread.CurrentThread.ManagedThreadId + ":" + CallContext.GetData ("test");}); Thread.Sleep Console.WriteLine ("Test: CallContext.LogicalSetData"); Task.Run () = > {CallContext.LogicalSetData ("test", "Duan Guangwei"); Console.WriteLine (Thread.CurrentThread.ManagedThreadId + ":" + CallContext.LogicalGetData ("test")); Task.Run () = > {Console.WriteLine (Thread.CurrentThread.ManagedThreadId + ":" + CallContext.LogicalGetData ("test");}); ExecutionContext.SuppressFlow () Task.Run (() = > {Console.WriteLine ("after SuppressFlow:" + CallContext.LogicalGetData ("test"));}); ExecutionContext.RestoreFlow (); Task.Run () = > {Console.WriteLine ("after RestoreFlow:" + CallContext.LogicalGetData ("test"));});})

Output

4. CallContext in Web

The storage of HttpContext.Current (including Session) is based on the CallContext of the current thread, and the current HttpContext cannot be obtained by non-request processing threads (that is, other threads) (not propagated across threads).

At this point, I believe you have a deeper understanding of "how C # uses CallContext to cache thread data". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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