What is reentrant function in embedded systems?
What is reentrant function in embedded systems?
A function is said to be reentrant if there is a provision to interrupt the function in the course of execution, service the interrupt service routine and then resume the earlier going on function, without hampering its earlier course of action.
What is difference between reentrant and thread safe code?
An operation is “thread-safe” if it can be performed from multiple threads safely, even if the calls happen simultaneously on multiple threads. An operation is re-entrant if it can be performed while the operation is already in progress (perhaps in another context).
What does reentrant mean in programming?
In computing, a computer program or subroutine is called reentrant if multiple invocations can safely run concurrently on multiple processors, or on a single processor system, where a reentrant procedure can be interrupted in the middle of its execution and then safely be called again (“re-entered”) before its previous …
What is the difference between reentrant and non reentrant functions?
A reentrant function does not hold static data over successive calls, nor does it return a pointer to static data. A reentrant function must not call non-reentrant functions. A non-reentrant function can often, but not always, be identified by its external interface and its usage.
How do you know if a code is reentrant?
1 Answer. The way to determine if a function is reentrant is to analyse what it does. 2) The code is not self-modifying (fortunately, self-modifying code is relatively rare in standard C or C++).
Which of the following is a reentrant function?
One function is said to be a reentrant function if there is a provision to interrupt that function in the course of execution, then service the ISR (Interrupt Service Routine) and then resume the task. This type of functions is used in different cases like, recursions, hardware interrupt handling.
Is reentrant thread-safe?
Non-reentrant functions usually are thread-unsafe, but making them reentrant often makes them threadsafe, too. In a multithreaded application program using the threads library, mutexes should be used for serializing shared resources.
How do you make a reentrant code?
To be reentrant, a computer program or routine:
- Must hold no static (or global) non-constant data.
- Must not return the address to static (or global) non-constant data.
- Must work only on the data provided to it by the caller.
- Must not rely on locks to singleton resources.
What means reentrant?
reentering or pointing inward: a reentrant angle. noun. a reentering angle or part. a person or thing that reenters or returns: Reentrants to the engineering program must take the introductory course again.
What is reentrant kernel?
A re-entrant kernel enables processes (or, to be more precise, their corresponding kernel threads) to give away the CPU while in kernel mode. They do not hinder other processes from also entering kernel mode. A typical use case is IO wait. The process wants to read a file.
Which is not a reentrant function?
A function can be non-reentrant if it uses memory that is not on the stack. If a function uses a static variable or a global variable, or a dynamically-allocated object that it finds for itself, then it is non-reentrant and any two calls to the function can interfere.
What is the use of reentrant function in C?
Reentrant functions are used in applications like hardware interrupt handling, recursion, etc. The function has to satisfy certain conditions to be called as reentrant: 1. It may not use global and static data.
Is reentrant a thread safe function?
In purely functional programming, reentrant often doesn’t imply thread safe, it would depend on the behavior of defined or anonymous functions passed to the function entry point, recursion, etc. A better way to put ‘thread safe’ is safe for concurrent access , which better illustrates the need.
What is a re-entrant in C++?
Reentrant is an attribute of a piece of code and basically means it can be re-entered by another execution flow, for example by an interrupt or by another task or thread. Generally speaking, a function produces output data based on some input data (though both are optional, in general). Shared data could be accessed by any function at any time.
What is a reentrant routine?
In the embedded world a routine must satisfy the following conditions to be reentrant: It uses all shared variables in an atomic way, unless each is allocated to a specific instance of the function. It does not call non-reentrant functions. It does not use the hardware in a non-atomic way. Quite a mouthful!
