gen/FreeBSD/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 $
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  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 The
  58 .Fn makecontext
  59 function
  60 modifies the user thread context pointed to by
  61 .Fa ucp ,
  62 which must have previously been initialized by a call to
  63 .Xr getcontext 3
  64 and had a stack allocated for it.
  65 The context is modified so that it will continue execution by invoking
  66 .Fn func
  67 with the arguments provided.
  68 The
  69 .Fa argc
  70 argument
  71 must be equal to the number of additional arguments provided to
  72 .Fn makecontext
  73 and also equal to the number of arguments to
  74 .Fn func ,
  75 or else the behavior is undefined.
  76 .Pp
  77 The
  78 .Fa "ucp->uc_link"
  79 argument
  80 must be initialized before calling
  81 .Fn makecontext
  82 and determines the action to take when
  83 .Fn func
  84 returns:
  85 if equal to
  86 .Dv NULL ,
  87 the process exits;
  88 otherwise,
  89 .Fn setcontext "ucp->uc_link"
  90 is implicitly invoked.
  91 .Pp
  92 The
  93 .Fn swapcontext
  94 function
  95 saves the current thread context in
  96 .Fa "*oucp"
  97 and makes
  98 .Fa "*ucp"
  99 the currently active context.
 100 .Sh RETURN VALUES
 101 If successful,
 102 .Fn swapcontext
 103 returns zero;
 104 otherwise \-1 is returned and the global variable
 105 .Va errno
 106 is set appropriately.
 107 .Sh ERRORS
 108 The
 109 .Fn swapcontext
 110 function
 111 will fail if:
 112 .Bl -tag -width Er
 113 .It Bq Er ENOMEM
 114 There is not enough stack space in
 115 .Fa ucp
 116 to complete the operation.
 117 .El
 118 .Sh SEE ALSO
 119 .Xr setcontext 3 ,
 120 .Xr ucontext 3