makecontext.2 (2010 09)

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makecontext(2) makecontext(2)

(Deprecated)

NAME

makecontext(), swapcontext() - manipulate user contexts

SYNOPSIS

#include <ucontext.h>

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

Deprecated

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

Deprecated

DESCRIPTION

The

makecontext()

function modiﬁes the context speciﬁed by ucp, which has been initialized using

getcontext(). When this context is resumed using

swapcontext() or setcontext(),program

execution continues by calling

func(), passing it the arguments that follow argc in the

makecon-

text() call.

Before a call is made to

makecontext()

, the context being modiﬁed should have a stack allocated for

it. The value of argc must match the number of integer arguments passed to

func(), otherwise the

behavior is undeﬁned.

The uc_link member is used to determine the context that will be resumed when the context being

modiﬁed by

makecontext()

returns. The uc_link member should be initialized prior to the call to

makecontext().

The

swapcontext() function saves the current context in the context structure pointed to by oucp and

sets the context to the context structure pointed to by ucp .

RETURN VALUE

On successful completion,

swapcontext() returns 0. Otherwise, −1 is returned and

errno is set to

indicate the error.

WARNINGS

makecontext() and swapcontext()

are deprecated and should be used only by legacy applications.

Context APIs are not recommended due to possible compatibility problems from release to release,

because context APIs are very architecture-speciﬁc. The context APIs "expose" the architecture to the

application, such that the application may not be compatible with all releases.

If you must use context APIs, be aware of the following:

• Do not copy the context yourself. It is not contiguous. The context may have pointers that may point

back to the original context rather than in the copied context; hence, it will be broken.

• The size of the context will vary in length from release to release.

ERRORS

The

makecontext() and swapcontext()

functions will fail if:

[ENOMEM] The ucp argument does not have enough stack left to complete the opera-

tion.