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6.  Safe and Unsafe Interfaces MT Interface Safety Levels Reentrant Functions for Unsafe Interfaces  Previous   Contents   Next 
   
 

Async-Signal-Safe Functions

Functions that can safely be called from signal handlers are Async-Signal-Safe. The POSIX standard defines and lists Async-Signal-Safe functions (IEEE Std 1003.1-1990, 3.3.1.3 (3)(f), page 55). In addition to the POSIX Async-Signal-Safe functions, these three functions from the Solaris threads library are also Async- Signal-Safe.

  • sema_post(3THR)

  • thr_sigsetmask(3THR), similar to pthread_sigmask(3THR)

  • thr_kill(3THR), similar to pthread_kill(3THR)

MT Safety Levels for Libraries

All routines that can potentially be called by a thread from a multithreaded program should be MT-Safe.

This means that 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 Table 6-3. Additional libraries will eventually be modified to be MT-Safe.

Table 6-3 Some MT-Safe Libraries

Library

Comments

lib/libc

Interfaces that are not safe have thread-safe interfaces of the form *_r (often with different semantics)

lib/libdl_stubs

To support static switch compiling

lib/libintl

Internationalization library

lib/libm

Math library compliant with System V Interface Definition, Edition 3, X/Open and ANSI C

lib/libmalloc

Space-efficient memory allocation library; see malloc(3X)

lib/libmapmalloc

Alternative mmap(2)-based memory allocation library; see mapmalloc(3X)

lib/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

lib/libresolv

Thread-specific errno support

lib/libsocket

Socket library for making network connections

lib/libw

Wide character and wide string functions for supporting multibyte locales

lib/straddr

Network name-to-address translation library

lib/libX11

X11 Windows library routines

lib/libC

C++ runtime shared objects

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.

 		 
 
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