What are the non-reentrant functions in C++?

Non-reentrant functions are functions that cannot be called by multiple threads at the same time. Some functions in the C standard library are non-reentrant, including input/output stream objects, time and date functions, and signal processing functions. , some mathematical functions, environment variable functions, and file system functions. Non-reentrant functions should be avoided in multi-threaded programs. If this cannot be avoided, preventive measures such as mutexes, atomic operations, or thread-local storage can be taken to ensure thread safety.

Non-reentrant functions in C

What is a non-reentrant function?

Non-reentrant functions refer to functions that cannot be called by multiple threads at the same time. If multiple threads call non-reentrant functions at the same time, unpredictable behavior may result, such as data corruption or program crashes.

Non-reentrant functions in C

Some functions in the C standard library are non-reentrant, including:

• Input/Output Stream Object (std::cin, std::cout, std::cerr)
• Time and date functions (std::time, std::localtime)
• Signal processing function (std::signal)
• Some mathematical functions (std::rand)
• Environment variable function (std::getenv)
• File system functions (such as std::ifstream and std::ofstream )

Avoid non-reentrant functions

In multi-threaded programs, avoid using non-reentrant functions. If they cannot be avoided, additional precautions must be taken to ensure thread safety. Typical solutions include:

• Mutex: A mutex is a lock that is used to ensure that only one thread can access a shared resource at the same time (such as non-repeatable into the function).
• Atomic operations: Atomic operations guarantee that data can be accessed and modified in an indivisible manner even in a multi-threaded environment.
• Thread Local Storage (TLS): TLS provides an isolated memory space for each thread, allowing threads to store private data without conflicting with other threads.

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