MT Safety Levels for Libraries

Language:

All routines that can potentially be called by a thread from a multithreaded program should be MT-Safe. Therefore, two or more activations of a routine must be able to correctly execute concurrently. So, every library interface that a multithreaded program uses must be MT-Safe.

Not all libraries are now MT-Safe. The commonly used libraries that are MT-Safe are listed in the following table. The libraries are accessed in the /usr/lib directory.

Table 18 Some MT-Safe Libraries

Library	Comments
`libc`	Interfaces that are not safe have thread-safe interfaces of the form `*_r`, often with different semantics.
`libm`	Math library that is compliant with System V Interface Definition, Edition 3, X/Open, and ANSI C
`libmalloc`	Space-efficient memory allocation library, see `malloc()`
`libmapmalloc`	Alternative `mmap`-based memory allocation library, see `mapmalloc()`
`libnsl`	The TLI interface, XDR, RPC clients and servers, `netdir`, `netselect` and `getXXbyYY` interfaces are not safe, but have thread-safe interfaces of the form `getXXbyYY_r`
`libresolv`	Domain name server library routines
`libsocket`	Socket library for making network connections
`libX11`	X11 Windows library routines
`libCrun`	C++ runtime shared objects for Oracle C++ 5.0 compilers
`libCstd`	C++ standard library for Oracle C++ 5.0 compilers
`libiostream`	Classic `iostream` library for Oracle C++ 5.0 compilers
`libC.so.5`	C++ runtime and `iostream` library for Oracle C++ 4.0 compilers

Unsafe Libraries

Routines in libraries that are not guaranteed to be MT-Safe can safely be called by multithreaded programs only when such calls are single threaded.