Multithreaded Programming Guide

MT Interface Safety Levels

The threads man pages, man(3t) , use the safety level categories listed in Table 6-1 to describe how well an interface supports threads (these categories are explained more fully in the Intro(3) reference manual page).

Table 6-1 Interface Safety Levels


Category	Description
Safe	This code can be called from a multithreaded application
Safe with exceptions	See the NOTES sections of these pages for a description of the exceptions.
Unsafe	This interface is not safe to use with multithreaded applications unless the application arranges for only one thread at a time to execute within the library.
MT-Safe	This interface is fully prepared for multithreaded access in that it is both safe and it supports some concurrency.
MT-Safe with exceptions	See the NOTES sections of these pages in the man(3t): Library Routines for a list of the exceptions.
Async-Signal-Safe	This routine can safely be called from a signal handler. A thread that is executing an Async-Signal-Safe routine does not deadlock with itself when it is interrupted by a signal.
Fork1-Safe	This interface releases locks it has held whenever the Solaris fork1(2) or the POSIX fork(2) is called.

See the table in Appendix C, MT Safety Levels: Library Interfaces, for the safety levels of interfaces from the man(3): Library Routines. Check the man page to be sure of the level.

Some functions have purposely not been made safe for the following reasons.

Making the interface MT-Safe would have negatively affected the performance of single-threaded applications.

The library has an Unsafe interface. For example, a function might return a pointer to a buffer in the stack. You can use reentrant counterparts for some of these functions. The reentrant function name is the original function name with "_r" appended.

Caution -

There is no way to be certain that a function with a name not ending in "_r" is MT-Safe other than by checking its reference manual page. Use of a function identified as not MT-Safe must be protected by a synchronizing device or by restriction to the initial thread.

Reentrant Functions for Unsafe Interfaces

For most functions with Unsafe interfaces, an MT-Safe version of the routine exists. The name of the new MT-Safe routine is always the name of the old Unsafe routine with "_r" appended. The Table 6-2 "_r" routines are supplied in the Solaris environment.

Table 6-2 Reentrant Functions


asctime_r(3c)	gethostbyname_r(3n)	getservbyname_r(3n)
ctermid_r(3s)	gethostent_r(3n)	getservbyport_r(3n)
ctime_r(3c)	getlogin_r(3c)	getservent_r(3n)
fgetgrent_r(3c)	getnetbyaddr_r(3n)	getspent_r(3c)
fgetpwent_r(3c)	getnetbyname_r(3n)	getspnam_r(3c)
fgetspent_r(3c)	getnetent_r(3n)	gmtime_r(3c)
`gamma_r(3m)`	getnetgrent_r(3n)	lgamma_r(3m)
getauclassent_r(3)	getprotobyname_r(3n)	localtime_r(3c)
getauclassnam_r(3)	getprotobynumber_r(3n)	nis_sperror_r(3n)
getauevent_r(3)	getprotoent_r(3n)	rand_r(3c)
getauevnam_r(3)	getpwent_r(3c)	readdir_r(3c)
getauevnum_r(3)	getpwnam_r(3c)	strtok_r(3c)
getgrent_r(3c)	getpwuid_r(3c)	tmpnam_r(3s)
getgrgid_r(3c)	getrpcbyname_r(3n)	ttyname_r(3c)
getgrnam_r(3c)	getrpcbynumber_r(3n)
gethostbyaddr_r(3n)	getrpcent_r(3n)