NAME

_lwp_ctl — prepare per-LWP communication area between kernel and userland

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <lwp.h>

int
_lwp_ctl(int features, struct lwpctl **address);

DESCRIPTION

_lwp_ctl() prepares per-LWP communication area for the calling LWP, and maps it into the calling process' address space. It takes the following arguments.

features

The bitwise-OR of the following flags.

LWPCTL_FEATURE_CURCPU

Request lc_curcpu.

LWPCTL_FEATURE_PCTR

Request lc_pctr.

address

The address to store a pointer to lwpctl structure for the calling LWP.

The per-LWP communication area is described by an lwpctl structure. It has following members, depending on features.

int lc_curcpu

The integral identifier of the CPU on which the LWP is running, or LWPCTL_CPU_NONE when the LWP is not running on any CPU. It's updated by the kernel and should be considered as read-only for userland. It's available only if requested with the LWPCTL_FEATURE_CURCPU flag.

int lc_pctr

The integer which is incremented on every context switches to the LWP. It can be used to detect preemption of the LWP. (thus its name "preemption counter".) It's updated by the kernel and should be considered as read-only for userland. It's available only if requested with the LWPCTL_FEATURE_PCTR flag.

RETURN VALUES

_lwp_ctl() returns 0 on success. Otherwise, -1 is returned and errno is set to indicate the error.

SEE ALSO

errno(2)