(use_cases_macro_relauncher_thread_test_cpp)=
# Macro "**relauncherCJitFunctionThreadTest.C**"

## Objective
	
The goal of this macro is to show how to handle thread-safe compiled function (or code) that would 
contain `TDataServer` objects (this is not particularly recommended, but has been requested to us). 
This example is only written in C++ as the CJit interface only works for this, but the idea is the 
same if one has a code and use the python interface. This will be further discussed below. The 
function is pointless, a pure illustrative toy and the results is not important as long as one sees 
that in one case, the macro runs smoothly while on the other hand, it crashes.

## Macro

{{
    "```{literalinclude} " + parent_dir
    + "/roottest/uranie/doc/relauncher/use_cases/cpp/relauncherCJitFunctionThreadTest.C"
    + "\n"
    + ":language: cpp\n"
    + ":lines: 1-50,53-60,63-66\n"
    + "```"
}}

The very first part of the macro is a function that would be applied to all points of our {{doe}}. 
The general context is simple: let's assume one wants to find the maximum value of a variable in a 
given dataset, and let's assume that this maximum should have to be scaled by some factor. We create 
the `multiply` function to do so, as done here:

{{
    "```{literalinclude} " + parent_dir
    + "/roottest/uranie/doc/relauncher/use_cases/cpp/relauncherCJitFunctionThreadTest.C"
    + "\n"
    + ":language: cpp\n"
    + ":lines: 1-17\n"
    + "```"
}}

In this function the dataset is always the same (`flowrateUniformDesign.dat`) and the multiplier is 
the only input attribute. The maximum of the dataset is found by creating a `TDataServer` object, by 
calling the `fileDataRead` method to read the dataset and by looping over the events (this is not at 
all the best way to do it, but it is a toy model to show what problems can arise when a `TDataServer` 
object is created in an evaluator use in multi-thread approach). Few important points in this 
function to prevent from race condition (not thread-safe behaviour):

- the `TDataServer` object is created statistically so that at the end of the function it is 
automatically destroyed;

- the line below is used to tell the `TDataServer` object not to write his data tree in the ROOT 
internal list and not to dump it in the archive file when the object is destroyed

    {{
        "```{literalinclude} " + parent_dir
        + "/roottest/uranie/doc/relauncher/use_cases/cpp/relauncherCJitFunctionThreadTest.C"
        + "\n"
        + ":language: cpp\n"
        + ":lines: 5\n"
        + "```"
    }}

- the line below is used to tell the `fileDataRead` method not to create the archive ROOT file once 
the dataset is read (thanks to the optional boolean set to false here)

    {{
        "```{literalinclude} " + parent_dir
        + "/roottest/uranie/doc/relauncher/use_cases/cpp/relauncherCJitFunctionThreadTest.C"
        + "\n"
        + ":language: cpp\n"
        + ":lines: 6\n"
        + "```"
    }}

The main function starts then with a block that allows to test the main point here: the method develop
by {{root}} to prevent the internal list to store object which would lead to race conditions. This 
block is commented to explain how to run the use-case macro discuss here. The important part is, if 
one wants to run the macro properly, to call 

{{
    "```{literalinclude} " + parent_dir
    + "/roottest/uranie/doc/relauncher/use_cases/cpp/relauncherCJitFunctionThreadTest.C"
    + "\n"
    + ":language: cpp\n"
    + ":lines: 28\n"
    + "```"
}}

Once this is done, then the macro can be briefly described in the few key steps

1. create the input (multiplier) and output (MultMean) attribute;

2. create the interface to the `multiply` function;

3. create the interface for the runner;

4. create the `TDataServer` object that would contain the multiplier and the results. This object is 
created within the `onMaster()` part because otherwise there would have been as many dataserver 
object as there are threads.

5. create a sampler and a {{doe}} to read 24 times the given dataset;

6. run the computations

At the end, once the macro is launched by using the command below, the

```bash
root -b -q relauncherCJitFunctionThreadTest.C
```

## Console

{{
    "```{literalinclude} " + parent_dir
    + "/roottest/build/uranie/doc/relauncher/use_cases/cpp/relauncherCJitFunctionThreadTest_clean.log"
    + "\n"
    + ":language: none\n"
    + ":lines: 4-\n"
    + "```"
}}