The include file <thread.h>, used with the -lthread library, compiles code that is upward compatible with earlier releases of the Solaris system. This library contains both interfaces--those with Solaris semantics and those with POSIX semantics. To call thr_setconcurrency(3T) with POSIX threads, your program needs to include <thread.h>.
The include file <pthread.h>, used with the -lpthread library, compiles code that is conformant with the multithreading interfaces defined by the POSIX 1003.1c standard. For complete POSIX compliance, the define flag _POSIX_C_SOURCE should be set to a (
long) value >= 199506:
cc [flags] file... -D_POSIX_C_SOURCE=N (where N 199506L)
You can mix Solaris threads and POSIX threads in the same application, by including both <thread.h> and <pthread.h>, and linking with either the -lthread or -lpthread library.
In mixed use, Solaris semantics prevail when compiling with -D_REENTRANT and linking with -lthread, whereas POSIX semantics prevail when compiling with -D_POSIX_C_SOURCE and linking with -lpthread.