The
pthread_attr_getstack() and
pthread_attr_setstack() functions get and set, respectively, the thread stack attributes
stackaddr and
stacksize in the
attr object. The remaining four functions behave similarly, but instead of getting or setting both
stackaddr and
stacksize, these get and set the values individually.
The
stacksize parameter is defined to be the minimum stack size (in bytes) allocated for the thread's stack during the creation of the thread. The
stackaddr attribute specifies the location of storage to be used for the thread's stack. All pages within the stack described by
stackaddr and
stacksize should be both readable and writable by the thread.
The behavior is undefined in all functions if the
attr parameter does not refer to an attribute object initialized by using
pthread_attr_init(3) prior to the call. In addition, undefined behavior may follow if the
pthread_attr_getstack() function is called before the
stackaddr attribute has been set.
Rationale
The rationale behind these functions is to address cases where an application may be used in an environment where the stack of a thread must be placed to some particular region of memory. For the majority of applications, this is seldom necessary, and the use of these functions should be generally avoided. At least few potential caveats can be mentioned.
•
There is a certain degree of ambiguity in the POSIX standard with respect to thread stack.
•
The exact behavior of the functions may vary both across machines and operating systems. In particular, the address specified by
stackaddr should be suitably aligned. The system page size, as specified by
sysconf(3), and the use of
posix_memalign(3) may guarantee some degree of portability. Also
mmap(2) provides means for alignment.
•
If the application modifies the stack address, it claims also the responsibility of allocating the stack area and guarding it against possible stack overflow. No default guard area will be allocated (see
pthread_attr_getguardsize(3)). It may be necessary to manually use
mprotect(2) in order to define a guard area at the end of the allocated stack.
•
Moreover, if
attr is used to create multiple threads, the stack address must be changed by the application between successive calls to
pthread_create(3).