to create a worker thread and keep it alive throughout my application life time to perform some back ground tasks

Question

I have a req where in i have to create a worker thread and keep it alive throughout my application life time to perform some back ground tasks . so is there any way i can stack tasks to this worker thread when ever needed by my application .?

Answer 1

Creating a thread is typically done by calling a special primitive (CreateThread() in Win32) and passing it an entry function. That function code in invoked in the newly spawned thread and can do whatever it wishes - for example, it could start a loop and peek tasks from a queue created in advance. Your main thread could post tasks to that queue so that the worker thread processes them. When there're no tasks in the queue the worker thread could simply block on a synchronization primitive (an event for example) waiting for new tasks to be posted.

Answer 2

Update: Even though you've indicated in comments you have to do this in Asp.Net, I'll leave my original content below, as it has some useful links.

Since Asp.Net uses the thread pool to schedule incoming requests, running your background task on the thread pool will take one thread off of it and will impact Asp.Net performance. Thus, you will have to use the Thread class.

To achieve your scenario, you can create a new Thread instance, set its IsBackground property to true and start it. Once started, the thread will wait for an AutoResetEvent (using the WaitOne method) to be set by an incoming request (using the Set met6hod), which will signal the background thread that its task should be processed. Once the task is finished, the background thread will again wait on the event.

This is the simplest implementation, which does not allow passing parameters between the request and the background thread and does not allow more than one tasks to be queued at a time. If you need support for parameters or queueing, you will have to keep a reference to the thread object somewhere it ill be accessible to the incoming requests.

You will also have to consider that your background thread can be killed at any point in time, if IIS decides to recycle the Asp.Net worker process. Also, throwing an exception inside the background thread will cause IIS to recycle the Asp.Net worker process.

There are also some considerations around the identity of the background thread. In particular, a background thread can't easily impersonate the identity of the user on the current incoming request. It is possible, but it will require you to pass the user identity each time a new task is scheduled by a request.

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It would be useful if you tell us what language and what platform you are writing your code in.

If it happens to be a Windows platform, there is a thread pool you can "borrow" threads from for your tasks. You can schedule your task on the thread pool by using either the QueueUserWorkItem API (C++) or the ThreadPool.QueueUserWorkItem (C#/.Net). Note there are some implications if your task will be running for a longer time.

You can also create your own thread using either the Thread class (C#/.Net) or the _beginthreadex or the CreateThread API (C++). In this case, you will have to implement a queue for the foreground thread to schedule the tasks on and you will have a loop on the background thread to pick the new tasks and execute them. And of course, you will have to synchronize the access to that queue from both threads using some synchronization primitive like a CRITICAL_SECTION (C++) or the lock statement (C#/.Net).

For Linux or OS X you might look into POSIX threads. I have not done much *nix style programming, so there might be even better alternatives. If you are targeting one of these platforms, add that info to your question and I am sure there will be helpful answers in no time.