CODEWITHSUNDEEP
c++multithreadingasync-awaitinteltbb
SMeyers
SMeyers

Reputation: 778

How to have a long waiting thread in Intel TBB?

I want to create a thread or task (more than one to be exact) that goes and does some non CPU intensive work that will take a lot of time because of external causes, such a HTTP request or a file IO operation from a slow disk. I could do this with async await in C# and would be exactly what i am trying to do here. Spawn a thread or task and let it do it's own thing while i continue with execution of the program and simply let it return the result whenever ready. The problem with TBB i have is that all tasks i can make think they are created for a CPU intensive work.

Is what TBB calls GUI Thread what i want in this case ? I would need more than one, is that possible ? Can you point me to the right direction ? Should i look for another library that provides threading and is available for multiple OS ?

Upvotes: 2

Views: 1679

Answers (2)

Brad Werth
Brad Werth

Reputation: 371

Any I/O blocking activity is poorly modeled by a task -- since tasks are meant to run to completion, it's just not what tasks are for. You will not find any TBB task-based approach that circumvents this. Since what you want is a thread, and you want it to work more-or-less nicely with other TBB code you already have, just use TBB's native thread class to solve the problem as you would with any other threading API. You won't need to set priority or anything else on this TBB-managed thread, because it'll get to its blocking call and then not take up any further time until the resource is available.

Upvotes: 2

JHumphrey
JHumphrey

Reputation: 999

About the only thing I can think of specifically in TBB is that a task can be assigned a priority. But this isn't the same thing as a thread priority. TBB task priorities only dictate when a task will be selected from the ready pool, but like you said - once the task is running, it's expected to be working hard. The way to do use this to solve the problem you mentioned is to break your IO work into segments, then submit them into the work pool as a series of (dependent) low-priority tasks. But I don't think this gets to your real problem ...

The GUI Thread you mentioned is a pattern in the TBB patterns document that says how to offload a task and then wait for a callback to signal that it's complete. It's not altogether different from an async. I don't think this solves your problem either.

I think the best way for you here is to make an OS-level thread. That's pthreads on Linux or windows threads on Windows. Then you'll want to call this on it: http://msdn.microsoft.com/en-us/library/windows/desktop/ms686277(v=vs.85).aspx ... if you happen to be in C++11, you could use a std::thread to create the thread and then call thread::native_handle to get a handle to call the Windows API to set the priority.

Upvotes: 1

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