Merge from vendor branch BZIP:
[dragonfly.git] / lib / libc / gen / makecontext.3
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36.\" $FreeBSD: src/lib/libc/gen/makecontext.3,v 1.4 2002/12/19 09:40:21 ru Exp $
37.\" $DragonFly: src/lib/libc/gen/makecontext.3,v 1.1 2007/01/16 07:16:23 dillon Exp $
38.\"
39.Dd September 10, 2002
40.Dt MAKECONTEXT 3
41.Os
42.Sh NAME
43.Nm makecontext , swapcontext
44.Nd modify and exchange user thread contexts
45.Sh LIBRARY
46.Lb libc
47.Sh SYNOPSIS
48.In ucontext.h
49.Ft void
50.Fo makecontext
51.Fa "ucontext_t *ucp"
52.Fa "void \*[lp]*func\*[rp]\*[lp]void\*[rp]"
53.Fa "int argc" ...
54.Fc
55.Ft int
56.Fn swapcontext "ucontext_t *oucp" "const ucontext_t *ucp"
57.Sh DESCRIPTION
58The
59.Fn makecontext
60function
61modifies the user thread context pointed to by
62.Fa ucp ,
63which must have previously been initialized by a call to
64.Xr getcontext 3
65and had a stack allocated for it.
66The context is modified so that it will continue execution by invoking
67.Fn func
68with the arguments provided.
69The
70.Fa argc
71argument
72must be equal to the number of additional arguments provided to
73.Fn makecontext
74and also equal to the number of arguments to
75.Fn func ,
76or else the behavior is undefined.
77.Pp
78The
79.Fa "ucp->uc_link"
80argument
81must be initialized before calling
82.Fn makecontext
83and determines the action to take when
84.Fn func
85returns:
86if equal to
87.Dv NULL ,
88the process exits;
89otherwise,
90.Fn setcontext "ucp->uc_link"
91is implicitly invoked.
92.Pp
93The
94.Fn swapcontext
95function
96saves the current thread context in
97.Fa "*oucp"
98and makes
99.Fa "*ucp"
100the currently active context.
101.Sh RETURN VALUES
102If successful,
103.Fn swapcontext
104returns zero;
105otherwise \-1 is returned and the global variable
106.Va errno
107is set appropriately.
108.Sh ERRORS
109The
110.Fn swapcontext
111function
112will fail if:
113.Bl -tag -width Er
114.It Bq Er ENOMEM
115There is not enough stack space in
116.Fa ucp
117to complete the operation.
118.El
119.Sh SEE ALSO
120.Xr setcontext 3 ,
121.Xr ucontext 3