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Do you know if the local variables of a functions or methods are created everytime the funtion is called?
That is, if I call a function from two diferent tasks simultaneously, or if I call a function from himself, every call has his own local variables created?
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There is TestAndSet in TwinCAT (I guess it is also in Codesys) which is used to block other tasks to access a code fragment... something along the lines of a critical section in C++.
One is to know if it is possible to use functions which can call himself (usefull when working with tree arrays for example)
The other is that I m not sure if I could use the same function (system time functions like getSystemTimeNs, if there exist a copy of his local variables in each call it is possible that there not exist any problem) in a hard real time task and in a freewheel task.
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Variables created within the scope of a method or function are dynamically created and destroyed with each invocation, making them reentrant. Exceptions to this are variables declared in a VAR_STAT section and pointers or references to statically defined variables.
If a function or method recursively calls itself the compiler will complain about not being able to calculate stack usage but there is an attribute pragma that can be used to control/suppress the warning. Presumably you know to limit call depth.
Variables created within the scope of a FB or PROG are statically created an maintain their values between invocations.
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Dears.
Do you know if the local variables of a functions or methods are created everytime the funtion is called?
That is, if I call a function from two diferent tasks simultaneously, or if I call a function from himself, every call has his own local variables created?
Hi Josep!
That's an interesting question.
There is TestAndSet in TwinCAT (I guess it is also in Codesys) which is used to block other tasks to access a code fragment... something along the lines of a critical section in C++.
See: l viewtopic.php?t=5042 l
They speak about CAA.TaskLock(); and CAA.TaskUnlock(); which look interesting.
Probably looking for information about those functions will lead you to the main point of your question.
Hope this helps even it is only a little.
Good luck and please, post the answer if you find it!
Best regards!
The question has two parts.
One is to know if it is possible to use functions which can call himself (usefull when working with tree arrays for example)
The other is that I m not sure if I could use the same function (system time functions like getSystemTimeNs, if there exist a copy of his local variables in each call it is possible that there not exist any problem) in a hard real time task and in a freewheel task.
Hi Josep,
Variables created within the scope of a method or function are dynamically created and destroyed with each invocation, making them reentrant. Exceptions to this are variables declared in a VAR_STAT section and pointers or references to statically defined variables.
If a function or method recursively calls itself the compiler will complain about not being able to calculate stack usage but there is an attribute pragma that can be used to control/suppress the warning. Presumably you know to limit call depth.
Variables created within the scope of a FB or PROG are statically created an maintain their values between invocations.