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RealView Libraries and Floating Point Support Guide
Preface Introduction The C and C++ Libraries About the C and C++ libraries
Features of the C and C++ libraries Namespaces Writing reentrant and thread‑safe code Introduction to reentrancy and thread‑safety Use of static data in the C libraries The __user_libspace static data area Managing locks in multithreaded applications Using the ARM C libraries with a multithreaded app Thread‑safety in the ARM C libraries Thread‑safety in the ARM C++ libraries Building an application with the C library Using the libraries with an application Building an application for a semihosted environme Building an application for a non semihosting envi Building an application without the C library Integer and FP helper functions Bare machine integer C Bare machine C with floating‑point Exploiting the C library The standalone C library functions Tailoring the C library to a new execution environ How C and C++ programs use the library functions __rt_entry Exiting from the program __rt_exit() __rt_lib_init() __rt_lib_shutdown() Tailoring static data access Tailoring locale and CTYPE using assembler macros Selecting locale at link time Selecting locale at runtime Defining a locale block LC_CTYPE data block LC_COLLATE data block LC_MONETARY data block LC_NUMERIC data block LC_TIME data block _get_lconv() localeconv() setlocale() _findlocale() The lconv structure Tailoring locale and CTYPE using C macros Selecting locale at link time Selecting locale at runtime Macros and utility functions _get_lc_ctype() _get_lc_collate() _get_lc_monetary() _get_lc_numeric() _get_lc_time() _get_lconv() localeconv() setlocale() _findlocale() __LC_CTYPE_DEF __LC_COLLATE_DEF __LC_TIME_DEF __LC_NUMERIC_DEF __LC_MONETARY_DEF __LC_INDEX_END The lconv structure Tailoring error signaling, error handling, and pro _sys_exit() errno __rt_errno_addr() __raise() __rt_raise() __default_signal_handler() _ttywrch() __rt_fp_status_addr() Tailoring storage management Avoiding the ARM‑supplied heap and heap‑using Support for malloc Tailoring the runtime memory model The memory models Controlling the runtime memory model Writing your own memory model __user_initial_stackheap() __user_setup_stackheap() __user_heap_extend() __user_heap_extent() __user_stack_cleanup_space() __rt_heap_extend() __rt_stack_postlongjmp() Tailoring the input/output functions Dependencies on low‑level functions Target‑dependent input/output support functions _sys_open() _sys_close() _sys_read() _sys_write() _sys_ensure() _sys_flen() _sys_seek() _sys_istty() _sys_tmpnam() _sys_command_string() #pragma import(_main_redirection) Tailoring other C library functions clock() _clock_init() time() remove() rename() system() getenv() _getenv_init() Selecting real‑time division ISO implementation definition ISO C library implementation definition Standard C++ library implementation definition C library extensions atoll() strtoll() strtoull() printf() snprintf() vsnprintf() lldiv() llabs() wcstombs() alloca() strlcpy() strlcat() _fisatty() __heapstats() __heapvalid() Library naming conventions Placing ARM libraries Helper libraries Identifying library variants The C Micro-library Floating‑point SupportManaging locks in multithreaded applications
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| Home > The C and C++ Libraries > Writing reentrant and thread‑safe code > Managing locks in multithreaded applications | |||
A thread‑safe function protects shared resources from concurrent access using locks. In RVCT v2.2 and above, there are functions that you can re-implement to enable you to manage the locking mechanisms and so prevent the corruption of shared data such as the heap. These functions have the prototypes:
_mutex_initialize()Accepts a pointer to a 32‑bit word and initializes it as a valid mutex.
int _mutex_initialize(mutex *m);By default,
_mutex_initialize()returns zero for a non threaded application. Therefore, in a multithreaded application,_mutex_initialize()must return a nonzero value on success so that, at runtime, the library knows that it is being used in a multithreaded environment._mutex_acquire()Causes the calling thread to obtain a lock on the supplied mutex.
void _mutex_acquire(mutex *m);_mutex_acquire()returns immediately if the mutex has no owner. If the mutex is currently owned by another thread,_mutex_acquire()must block it until it becomes available._mutex_release()This causes the calling thread to release the supplied mutex.
void _mutex_release(mutex *m);_mutex_release()assumes that the mutex is owned by the calling thread.
For the C library, a mutex is specified as a single 32‑bit word of memory that can be placed anywhere. However, if your mutex implementation requires more space than this, or demands that the mutex be in special memory area, then you must treat the default mutex as a pointer to a real mutex.
| Copyright © 2007 ARM Limited. All rights reserved. | ARM DUI 0378A |
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