mirror of https://github.com/mkerrisk/man-pages
84 lines
3.4 KiB
Groff
84 lines
3.4 KiB
Groff
.\" Copyright (C) 2001 Andries Brouwer (aeb@cwi.nl)
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.TH MAKECONTEXT 3 2001-11-15 "Linux 2.4" "Linux Programmer's Manual"
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.SH NAME
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makecontext, swapcontext \- manipulate user context
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.SH SYNOPSIS
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.B #include <ucontext.h>
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.sp
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.BI "void makecontext(ucontext_t *" ucp ", void *" func (),
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.BI "int " argc ", ...);"
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.br
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.BI "int swapcontext(ucontext_t *" oucp ", ucontext_t *" ucp );
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.SH DESCRIPTION
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In a System V-like environment, one has the type \fBucontext_t\fP defined in
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.I <ucontext.h>
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and the four functions
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\fBgetcontext\fP(), \fBsetcontext\fP(), \fBmakecontext\fP()
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and \fBswapcontext\fP() that allow user-level context switching
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between multiple threads of control within a process.
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.LP
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For the type and the first two functions, see
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.BR getcontext (2).
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.LP
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The \fBmakecontext\fP() function modifies the context pointed to
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by \fIucp\fP (which was obtained from a call to \fBgetcontext\fP()).
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Before calling \fBmakecontext\fP(), one should allocate a new stack
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for this context, assigning to \fIucp->uc_stack\fP, and define a
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successor context, assigning to \fIucp->uc_link\fP.
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When this context is later activated (using \fBsetcontext\fP() or
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\fBswapcontext\fP()) then first the function \fIfunc\fP is called,
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with the arguments specified following \fIargc\fP (where \fIargc\fP
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must contain the number of these arguments), and when this function
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returns, the successor context is activated. When the successor context
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pointer is NULL, the thread exits.
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.LP
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The \fBswapcontext\fP() function saves the current context in
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the structure pointed to by \fIoucp\fP, and then activates the
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context pointed to by \fIucp\fP.
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.SH "RETURN VALUE"
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When successful, \fBswapcontext\fP()
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does not return. (But we may return later, in case \fIoucp\fP is
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activated, in which case it looks like \fBswapcontext\fP() returns 0.)
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On error, \fBswapcontext\fP() returns \-1 and
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sets \-1 \fIerrno\fP appropriately.
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.SH ERRORS
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.TP
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.B ENOMEM
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Insufficient stack space left.
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.SH NOTES
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The interpretation of \fIucp->uc_stack\fP is just as in
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.BR sigaltstack (2),
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namely, this struct contains start and length of a memory area
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to be used as stack, regardless of the direction of growth of
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the stack. So, it is not necessary for the user program to
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worry about this direction.
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.SH "CONFORMING TO"
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SUSv2, POSIX 1003.1-2001.
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.SH "SEE ALSO"
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.BR getcontext (2),
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.BR sigaction (2),
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.BR sigaltstack (2),
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.BR sigprocmask (2),
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.BR sigsetjmp (3)
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