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 $
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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]\*[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 (of type
  68 .Ft int )
  69 provided.
  70 The
  71 .Fa argc
  72 argument
  73 must be equal to the number of additional arguments provided to
  74 .Fn makecontext
  75 and also equal to the number of arguments to
  76 .Fn func ,
  77 or else the behavior is undefined.
  78 .Pp
  79 The
  80 .Fa "ucp->uc_link"
  81 argument
  82 must be initialized before calling
  83 .Fn makecontext
  84 and determines the action to take when
  85 .Fn func
  86 returns:
  87 if equal to
  88 .Dv NULL ,
  89 the process exits;
  90 otherwise,
  91 .Fn setcontext "ucp->uc_link"
  92 is implicitly invoked.
  93 .Pp
  94 The
  95 .Fn swapcontext
  96 function
  97 saves the current thread context in
  98 .Fa "*oucp"
  99 and makes
 100 .Fa "*ucp"
 101 the currently active context.
 102 .Sh RETURN VALUES
 103 If successful,
 104 .Fn swapcontext
 105 returns zero;
 106 otherwise \-1 is returned and the global variable
 107 .Va errno
 108 is set appropriately.
 109 .Sh ERRORS
 110 The
 111 .Fn swapcontext
 112 function
 113 will fail if:
 114 .Bl -tag -width Er
 115 .It Bq Er ENOMEM
 116 There is not enough stack space in
 117 .Fa ucp
 118 to complete the operation.
 119 .El
 120 .Sh SEE ALSO
 121 .Xr setcontext 3 ,
 122 .Xr ucontext 3