Multithreaded Programming Guide

MT Interface Safety Levels

The threads man pages, man(3THR), 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(3THR)`: 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 section 3 manual pages for the safety levels of library routines.

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)