Is Function.calculate(<args>) thread safe?

[darxis]

In case of parallel process remember to create static objects separately for each process, otherwise you will get strange conflicts, errors as multiple processes will change the object state. So - If 8 processes then 8 different static functions.

Originally posted by @mariuszgromada in #134 (comment)

Is Function.calculate(params double[] parameters) thread safe or not?

I have the following two pieces of code, one with a lock and the other one without

lock (_lock)
{
    result = function.calculate(argumentValues);
}

result = function.calculate(argumentValues);

I am using many parallel threads calling function.calculate on the same function instance. The code without the lock seems to be much much much slower, I have not measured time, but I think it goes in seconds for some calculations instead of milliseconds for the code with the lock. Maybe this is caused by the locks that mxparser uses internally that are not FIFO?

[mariuszgromada]

Dear @darxis

Sorry for the late response. Generally it is a bad idea to use the same instance of function in many paralel threads. Function.calculate(params double[] parameters) calls Function.setArgumentValue(int argumentIndex, double argumentValue) many times in order to set all parameters and then Function.calculate() to bring the function value. It means that the state of the object is modified many times in one call of Function.calculate(params double[] parameters). It might happen that the other thread is using Function.setArgumentValue(int argumentIndex, double argumentValue) directly, building the parameters value one by one, and your call of Function.calculate(params double[] parameters) will destroy it.

Best regards

[TaIos]

This is (in my opinion) a huge drawback of a org.mariuszgromada.math.mxparser.Function#calculate(double...)

Every user of this library has to build around it if there is a need for a thread-safe computation.

My solution was to create multiple instances of Function and cycle through them. There even isn't a fast way of how to create a copy of an already existing Function.

However, despite this drawback, I find it very easy to use and I like it the most among other similar libraries.

[mariuszgromada]

Dear @TaIos Thank you. I will solve this by providing very convenient method to make a function clone + showing in tutorial how to do it properly.

Best regards

[mariuszgromada]

The Function clone is already there, but is a private constructor Function(Function f) as I am using it only in case of recursive function declaration - so I will make a public method clone() that referes to this private construnctor Function(Function f).

https://github.com/mariuszgromada/MathParser.org-mXparser/blob/9434b30522b1f2d6e260543dd03d0414d16d6841/CURRENT/java/src/org/mariuszgromada/math/mxparser/Function.java#LL499C6-L499C6

Best regards

[mariuszgromada]

Done, details are here #293