Thread-Local Storage

C99

• ISO/IEC 9899:1999 is amended by gcc and others to introduce the __thread storage specifier (§6.2.4, §6.4.1, §6.7.1), and to add a vague definition of threads to the execution model (§5.1.2).

C++11

• C++11 adds the thread_local keyword
  • Only constant initializers can be used for variables having __thread storage.

Windows

• __declspec(thread) doesn't work in DLL's prior to Vista when loaded via LoadLibrary().
  • The DLL must be linked into the binary before the binary's main image is loaded.

See Also

• pthreads
• Ulrich Drepper's paper, "ELF Handling for Thread-Local Storage"
• gcc's Info entry for TLS
• "C and C++ Thread Compatibility", ISO/IEC JTC1 SC22 WG14 N1423 (Lawrence Crowl)