NAME

makecontext, swapcontext - manipulate user contexts

SYNOPSIS

#include <ucontext.h>

void  makecontext  (ucontext_t  *ucp,  (void(*)())func,  int
argc,...);

int swapcontext (ucontext_t *oucp, ucontext_t *ucp);

DESCRIPTION

These functions are useful for implementing user-level context switching between multiple threads of control within a process.

makecontext modifies the context specified by ucp, which has been initialized using getcontext; when this context is resumed using swapcontext or setcontext [see getcontext(2)], program execution continues by calling the function func, passing it the arguments that follow argc in the makecontext call. The integer value of argc must match the number of arguments that follow argc. Otherwise the behavior is undefined.

swapcontext saves the current context in the context structure pointed to by oucp and sets the context to the context structure pointed to by ucp.

These functions will fail if either of the following is true:

ENOMEM ucp does not have enough stack left to complete the operation.

EFAULT ucp or oucp points to an invalid address.

SEE ALSO

exit(2), getcontext(2), sigaction(2), sigprocmask(2),  ucon-
text(5).

DIAGNOSTICS

On successful completion, swapcontext return a value of zero. Otherwise, a value of -1 is returned and errno is set to indicate the error.

NOTES

The size of the ucontext_t structure may change in future releases. To remain binary compatible, users of these features must always use makecontext or getcontext to create new instances of them.