Thread‑safety in the ARM C++ libraries

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2.2.7. Thread‑safety in the ARM C++ libraries

The following summarizes thread‑safety in the C++ libraries:

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, malloc(), and free(). 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 is 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‑implementing, the following construction of lsobj can be made thread‑safe:
```
struct T { T(); };
void f() { static T lsobj; }
```
See the CPPABI for information on the __cxa_ and __aeabi_ functions.
Throwing an exception is thread‑safe if any user constructors and destructors that get called are also thread‑safe. See the Exception Handling ABI for the ARM Architecture for more information.
The ARM C++ library uses the ARM C library. To use the ARM C++ library in a multithreaded environment, you must provide the functions described in Using the ARM C libraries with a multithreaded application.

Copyright © 2007 ARM Limited. All rights reserved.	ARM DUI 0378A
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