Context

Whenever you use multi threading in an application, either by using AsyncHelperBase for a UIController or by service mutliple requests for the iis in parallel, the class called Firefly.Box.Context comes into play.

Each thread will have it's own instance of the class called Firefly.Box.Context, you can access the context of the current thread by using the Current property of the class Firefly.Box.Context. To list all the current active contexts you can use the Firefly.Box.Context.ActiveContexts class.

The Context class is responsible for keeping information that is relevant only for the current thread and making sure that each thread get's it's own separated values.

When ever you run a controller using the AsyncHelperBase class or recieve a new request - a new Context instance is created to serve that thread.

Once the work is done, the Context is disposed and all it's assets are disposed.

The following topics should be considered:

  1. Each context has it's own Controller Stack - you can see it in Firefly.Box.Context.Current.ActiveTasks
  2. Each context has it's own connections to the database and it's own transactions
  3. Each context has it's own instance of the Application class this means that when you set a value to a column that is defined in the Application class, it only affects that specific context.
  4. Application's OnStart event is executed when ever the first controller is called. - this means that it'll get executed when you calll using AsyncHelperBase class or when a new web request is served.

when usign AsyncHelperBase class you can controll that behaviour with the DisableApplicationStart flag.

  1. By default Memory Tables are not shared between contexts.
  2. ParametersInMemory (getparam, setparam) are not shared between contexts - if you want to share values between contexts, use SharedValSet and SharedValGet
  3. Ini values that are set using u.IniSet('xx',false) are not shared between contexts - each context will have it's own values.

Sharing Data Between Threads

You can share data between threads by using the C# static keyword. For Example:

class MyClass
{
	public static string CustomerName = "Important Customer";
} 

Saving Context Specific Data

There are two ways to save data per context - that will still be available in the context of that specific context.

1. Use the Context Object

Setting a context specific value:

//set the value
Firefly.Box.Context.Current["CustomerName"] = "Important Customer";
//get the value
System.Diagnostics.Debug.WriteLine(Firefly.Box.Context.Current["CustomerName"]);
//List value from all Current Contexts:
foreach (var item in Firefly.Box.Context.ActiveContexts)
{
    System.Diagnostics.Debug.WriteLine(item["CustomerName"];
} 

note that every value that is stored in the context and implements the IDisposable interface will get disposed when the context is disposed.

2. Using Context Static

You can use the generic ContextStatic class to maintain the ease of use of static with the Context separation.

public static ContextStatic<string> CustomerName = new ContextStatic<string>(() => "Default Value"); 
// set the value for the current context
CustomerName.Value = "Important Customer";
// get the value
System.Diagnostics.Debug.WriteLine(CustomerName.Value);
//List value from all Current Contexts:
foreach (var item in Firefly.Box.Context.ActiveContexts)
{
    System.Diagnostics.Debug.WriteLine( CustomerName.GetValueFromContext(item));
} 

this is better than using the [ThreadStatic] attribute since threads get reused and the ContextStatic is cleared and refreshed

Important note

When you create your own threads, or use a non migrated web code that calls migrated code - make sure to call Firefly.Box.Context.Current.Dispose() when you are done, to close all active connections and release all context specific resources.

Interesting codes to review in ENV

  1. RaiseOnContext and RaiseOnContextPrivate method in ControllerBase
  2. UserMethods.CtxGetId
  3. UserMethods.CtxSetName
  4. UserMethods.CtxGetAllNames
  5. UserMethods.CtxNum
  6. UserMethods.SetContextFocus
  7. UserMethods.DoOnContext
  8. UserMethods.CtxKill
  9. UserMethods.CtxLstUse
  10. UserMethods.CtxProg
  11. UserMethods.CtxClose
  12. UserMethods.CtxStat
  13. UserMethods.Prog


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