MT Interface Safety Levels

The man pages for functions and interfaces indicate how well the function or interface supports threads. The ATTRIBUTES section of each man page lists the MT-Level attribute, which is set to one of the safety level categories listed in Table 7-1. These categories are explained more fully in the attributes(5) man page.

If a man page does not state explicitly that a function is MT-Safe, you must assume that the function is unsafe.

Table 7-1 Interface Safety Levels

Category	Description
Safe	This code can be called from a multithreaded application
Safe with exceptions	See the NOTES sections of the man page 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. The interface is both safe and supports some concurrency.
MT-Safe with exceptions	See the NOTES sections of the man page for a description 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 interrupted by a signal. See Async-Signal-Safe Functions in Oracle Solaris Threads
Fork1–Safe	This interface releases locks it has held whenever Oracle Solaris `fork1`(2) or POSIX `fork`(2) is called.

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

The interface made 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 re-entrant counterparts for some of these functions. The re-entrant function name is the original function name with “_r” appended.

Note - The only way to be certain that a function with a name not ending in “_r” is MT-Safe is to check the function's 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 MT-Safe routine is the name of the Unsafe routine with “_r” appended. For example, the MT-Safe version of asctime() is asctime_r(). The Table 7-2 “_r” routines are supplied in the Oracle Solaris environment.

Table 7-2 Reentrant Functions

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

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	Multithreaded Programming Guide Oracle Solaris 11.1 Information Library