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Libraries and Floating Point Support Guide

Preface The ARM C and C++ Libraries Mandatory linkage with the C library C and C++ runtime libraries Summary of the C and C++ runtime libraries Compliance with the Application Binary Interface ( Increasing portability of object files to other CL ARM C and C++ library directory structure Selection of ARM C and C++ library variants based Thumb C libraries C and C++ library features C++ and C libraries and the std namespace Multithreaded support in ARM C libraries ARM C libraries and multithreading ARM C libraries and reentrant functions ARM C libraries and thread-safe functions Use of static data in the C libraries Use of the __user_libspace static data area by the C library functions to access subsections of the _ Re-implementation of legacy function __user_libspa Management of locks in multithreaded applications How to ensure re-implemented mutex functions are c Using the ARM C library in a multithreaded environ Thread safety in the ARM C library Thread safety in the ARM C++ library The floating-point status word in a multithreaded Support for building an application with the C lib Using the C library with an application Using the C and C++ libraries with an application Using $Sub$$ to mix semihosted and nonsemihosted I Using the libraries in a nonsemihosting environmen C++ exceptions in a non-semihosting environment Direct semihosting C library function dependencies Indirect semihosting C library function dependenci C library API definitions for targeting a differen Support for building an application without the C Building an application without the C library Creating an application as bare machine C without Integer and floating-point compiler functions and Bare machine integer C Bare machine C with floating-point processing Customized C library startup code and access to C Using low-level functions when exploiting the C li Using high-level functions when exploiting the C l Using malloc() when exploiting the C library Tailoring the C library to a new execution environ Initialization of the execution environment and ex C++ initialization, construction and destruction Exceptions system initialization Emergency buffer memory for exceptions Library functions called from main() Program exit and the assert macro Assembler macros that tailor locale functions in t Link time selection of the locale subsystem in the Runtime selection of the locale subsystem in the C Definition of locale data blocks in the C library LC_CTYPE data block LC_COLLATE data block LC_MONETARY data block LC_NUMERIC data block LC_TIME data block Modification of C library functions for error sign Stack and heap memory allocation and the ARM C and Library heap usage requirements of the ARM C and C Choosing a heap implementation for memory allocati Stack pointer initialization and heap bounds Legacy support for __user_initial_stackheap() Avoiding the heap and heap-using library functions Tailoring input/output functions in the C and C++ Target dependencies on low-level functions in the The C library printf family of functions The C library scanf family of functions Redefining low-level library functions to enable d The C library functions fread(), fgets() and gets( Re-implementing __backspace() in the C library Re-implementing __backspacewc() in the C library Redefining target-dependent system I/O functions i Tailoring non-input/output C library functions Real-time integer division in the ARM libraries ISO C library implementation definition How the ARM C library fulfills ISO C specification mathlib error handling ISO-compliant implementation of signals supported ISO-compliant C library input/output characteristi Standard C++ library implementation definition C library functions and extensions Compiler generated and library-resident helper fun C and C++ library naming conventions Using macro__ARM_WCHAR_NO_IO to disable FILE decla Using library functions with execute-only memory The ARM C Micro-library Floating-point Support The C and C++ Library Functions reference Floating-point Support Functions Reference

Thread safety in the ARM C++ library

1.5.12 Thread safety in the ARM C++ library

ARM C++ library functions are either always thread-safe, never thread-safe, or thread-safe in certain circumstances.

The following points summarize thread safety in the C++ library:
  • The function std::set_new_handler() is not thread-safe. This means that some forms of ::operator new and ::operator delete are not thread-safe with respect to std::set_new_handler():
    • The default C++ runtime library implementations of the following use malloc() and free() and are thread-safe with respect to each other. They are not thread-safe with respect to std::set_new_handler(). You are permitted to replace them:
      ::operator new(std::size_t)
      ::operator new[](std::size_t)
      ::operator new(std::size_t, const std::nothrow_t&)
      ::operator new[](std::size_t, const std::nothrow_t)
      ::operator delete(void*)
      ::operator delete[](void*)
      ::operator delete(void*, const std::nothrow_t&)
      ::operator delete[](void*, const std::nothrow_t&)
    • The following placement forms are also thread-safe. You are not permitted to replace them:
      ::operator new(std::size_t, void*)
      ::operator new[](std::size_t, void*)
      ::operator delete(void*, void*)
      ::operator delete[](void*, void*)
  • Construction and destruction of global objects are not thread-safe.
  • Construction of local static objects can be made thread-safe if you re-implement the functions __cxa_guard_acquire(), __cxa_guard_release(), __cxa_guard_abort(), __cxa_atexit() and __aeabi_atexit() appropriately. For example, with appropriate re-implementation, the following construction of lsobj can be made thread-safe:
    struct T { T(); };
    void f() { static T lsobj; }
  • Throwing an exception is thread-safe if any user constructors and destructors that get called are also thread-safe.
  • The ARM C++ library uses the ARM C library. To use the ARM C++ library in a multithreaded environment, you must provide the same functions that you would be required to provide when using the ARM C library in a multithreaded environment.

Rogue Wave Standard C++ library

The Rogue Wave Standard C++ library is a part of the ARM C++ library. What applies to the ARM C++ library applies to the Rogue Wave Standard C++ library too. In the Rogue Wave Standard C++ library, specifically:
  • All containers and all functions are reentrant, making no use of internal, modifiable static data.
    • Except for the std::random_shuffle function, which uses static data to record the state of the random number generator.
  • The iostream and locale classes are not thread safe.
You must protect shared objects while using the iostream and locale classes, and the std::random_shuffle function. To do this, you might use mutex functions, or co-operative threading. As an example, in a typical case of a pre-emptive multitasking environment, one that uses mutex functions with containers, this means that:
  • Reader threads can safely share a container if no thread writes to it during the reads.
  • While a thread writes to a shared container, you must apply locking around the use of the container.
  • Writer threads can write to different containers safely.
  • You must apply locking around the use of random_shuffle.
  • Multiple threads cannot use iostream and locale classes safely unless you apply locking around the use of their objects.
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