PTHREAD_ATTR_GETSTACK(3)

NAME
pthread_attr_getstack, pthread_attr_setstack, pthread_attr_getstacksize, pthread_attr_setstacksize, pthread_attr_getstackaddr, pthread_attr_setstackaddr - get and set thread stack attributes

LIBRARY
libpthread

SYNOPSIS
#include <pthread.h>
int
pthread_attr_getstack(const pthread_attr_t * restrict attr, void ** restrict stackaddr, size_t * restrict stacksize);
int
pthread_attr_setstack(pthread_attr_t * restrict attr, void *stackaddr, size_t stacksize);
int
pthread_attr_getstacksize(const pthread_attr_t * restrict attr, size_t * restrict stacksize);
int
pthread_attr_setstacksize(pthread_attr_t *attr, size_t stacksize);
int
pthread_attr_getstackaddr(const pthread_attr_t * restrict attr, void ** restrict stackaddr);
int
pthread_attr_setstackaddr(pthread_attr_t *attr, void *stackaddr);

DESCRIPTION
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).

RETURN VALUES
If successful, these functions return 0. Otherwise, an error number is returned to indicate the error.

ERRORS
No errors are defined for the three functions that obtain the stack values. The three functions that set the stack values may fail if:

[ENOMEM]
    There was insufficient memory to complete the operation.

The pthread_attr_setstacksize() function may additionally fail if:

[EINVAL]
    The specified stacksize is less than PTHREAD_STACK_MIN or exceeds some system-imposed limit.

SEE ALSO
pthread_attr(3), pthread_attr_setguardsize(3)

STANDARDS
All described functions conform to p1003.1-2001. Note that pthread_attr_getstackaddr() and pthread_attr_setstackaddr() were however removed from the specification in the p1003.1-2008 revision.

BUGS
Older versions of NetBSD, prior to 10.0, 9.4, and 8.3, incorrectly adjust the stack address by the guard size in threads configured with pthread_attr_setstack(), instead of ignoring the guard size in that case as POSIX prescribes ( see PR lib/57721: https://gnats.NetBSD.org/57721).

Even if you didn't set a nonzero guard size with pthread_attr_setguardsize(3), the system will choose a nonzero default guard size.

To work around this in applications that run on older and newer versions of NetBSD, as well as on other operating systems, you can safely set the guard size to zero:
    pthread_attr_setguardsize(&attr, 0);