xref: /freebsd/lib/libc/gen/makecontext.3 (revision 304d1f73fe42cfcdd62440886708ff6b79c6975a)
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36.\" $FreeBSD$
37.\"
38.Dd September 10, 2002
39.Dt MAKECONTEXT 3
40.Os
41.Sh NAME
42.Nm makecontext , swapcontext
43.Nd modify and exchange user thread contexts
44.Sh LIBRARY
45.Lb libc
46.Sh SYNOPSIS
47.In ucontext.h
48.Ft void
49.Fo makecontext
50.Fa "ucontext_t *ucp"
51.Fa "void \*[lp]*func\*[rp]\*[lp]void\*[rp]"
52.Fa "int argc" ...
53.Fc
54.Ft int
55.Fn swapcontext "ucontext_t *oucp" "const ucontext_t *ucp"
56.Sh DESCRIPTION
57.Fn makecontext
58modifies the user thread context pointed to by
59.Fa ucp ,
60which must have previously been initialized by a call to
61.Xr getcontext 3
62and had a stack allocated for it.
63The context is modified so that it will continue execution by invoking
64.Fn func
65with the arguments provided.
66.Fa argc
67must be equal to the number of additional arguments provided to
68.Fn makecontext
69and also equal to the number of parameters to
70.Fn func ,
71or else the behavior is undefined.
72.Pp
73.Fa "ucp->uc_link"
74must be initialized before calling
75.Fn makecontext
76and determines the action to take when
77.Fn func
78returns:
79if equal to
80.Dv NULL ,
81the process exits;
82otherwise,
83.Fn setcontext "ucp->uc_link"
84is implicitly invoked.
85.Pp
86.Fn swapcontext
87saves the current thread context in
88.Fa "*oucp"
89and makes
90.Fa "*ucp"
91the currently active context.
92.Sh RETURN VALUES
93If successful,
94.Fn swapcontext
95returns zero;
96otherwise \-1 is returned and the global variable
97.Va errno
98is set appropriately.
99.Sh ERRORS
100.Fn swapcontext
101will fail if:
102.Bl -tag -width Er
103.It Bq Er ENOMEM
104There is not enough stack space in
105.Fa ucp
106to complete the operation.
107.El
108.Sh SEE ALSO
109.Xr setcontext 3 ,
110.Xr ucontext 3
111