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undocumented - LibraryLink: Asynchronous Examples


Inside the directory structure of LibraryLink there are several example files. Basically, they are divided in two types:



  • Synchronous: demo.c, demo_error.c, demo_eval.c, demo_mathlink.c, demo_numerical.c, demo_shared.c, demo_string.c


  • Asynchronous: async-examples-libmain.c, async-tasks-oneshot.c, async-tasks-repeating.c, async-tasks-timing.c, async-tasks-without-thread.c


The synchronous examples are well documented and relatively easy to use. However, the asynchronous are undocumented (as far as I know) and more difficult to use. So far, after some guesswork, the best I could figure it out is the following:


File Description



  • async-examples-libmain.c: Initialization instructions (nothing to be executed within Mathematica).

  • async-tasks-oneshot.c: Example of how to execute a task one single time and then close it.

  • async-tasks-repeating.c: Example of how to execute a task continuously. This can be seen at the function IntBackgroundTask which has a while loop to keep the task alive.

  • async-tasks-timing.c: Example of how to execute a task with time constraint. This can be seen at the function IntBackgroundTask which has a for loop limited by an iterator.

  • async-tasks-without-thread.c: ????



File Structure
The main function of each one of the files is start_*_background_task and they are all very similar:



  • The arguments are the same as of the synchronous ones (ie: always 3 arguments).

  • The lines between mint asyncObjID; and asyncObjID = ioLibrary->createAsynchronousTaskWithThread(IntBackgroundTask, threadArg); sets and creates the asynchronous task.

  • MArgument_setInteger returns a value to Mathematica, currently is returning only the value of asyncObjID. However, more calculations could be copy & paste before this line.



1st Issue

My guesswork is correct? Did I miss something?


2nd Issue
What the example file async-tasks-without-thread.c do?


3rd Issue
I'm trying to create a library for each one of the aforementioned files but some of them are not working. For example, when I execute the following:


<< CCompilerDriver`
demoFile = First@FileNames["async-tasks-oneshot.c", {$InstallationDirectory}, Infinity];
lib = CreateLibrary[{demoFile}, "mylib"];

I receive the following error message:



CreateLibrary::cmperr: Compile error: C:\Program Files\Wolfram Research\Mathematica\9.0\SystemFiles\Links\LibraryLink\LibraryResources\Source\async-tasks-oneshot.c(5) : fatal error C1083: Cannot open include file: 'async-examples.h': No such file or directory >>

The same happens with "async-tasks-repeating.c" and "async-tasks-without-thread.c".


What is going on? How to fix it?


4th Issue
If I just load the library (instead of creating it), I also get some behaviours not understood yet. For example:


fun = LibraryFunctionLoad["async-tasks-oneshot", "start_int_background_task", {Integer, Integer}, Integer];
fun[0, 0]

Out[2]:=1


I was expecting the output to be asyncObjID due the line MArgument_setInteger(Res, asyncObjID). Why this is not the case?


5th Issue
Moreover, after calling this fun[0,0], I can not evaluate anything else. For example:


1+1

It stays in the evaluation queue forever, but never returns an answer. Why this is happening? How to properly call the asynchronous function fun?



ps: Anticipating some comments, I'm trying to use this asynchronous feature in order to solve an issue with Low Level Networking Programming.




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