gen/FreeBSD/getcontext.3

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  36 .\" $FreeBSD: src/lib/libc/gen/getcontext.3,v 1.3 2004/12/03 14:10:04 rse Exp $
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  38 .Dd September 10, 2002
  39 .Dt GETCONTEXT 3
  40 .Os
  41 .Sh NAME
  42 .Nm getcontext , setcontext
  43 .Nd get and set user thread context
  44 .Sh LIBRARY
  45 .Lb libc
  46 .Sh SYNOPSIS
  47 .In ucontext.h
  48 .Ft int
  49 .Fn getcontext "ucontext_t *ucp"
  50 .Ft int
  51 .Fn setcontext "const ucontext_t *ucp"
  52 .Sh DESCRIPTION
  53 The
  54 .Fn getcontext
  55 function
  56 saves the current thread's execution context in the structure pointed to by
  57 .Fa ucp .
  58 This saved context may then later be restored by calling
  59 .Fn setcontext .
  60 .Pp
  61 The
  62 .Fn setcontext
  63 function
  64 makes a previously saved thread context the current thread context, i.e.,
  65 the current context is lost and
  66 .Fn setcontext
  67 does not return.
  68 Instead, execution continues in the context specified by
  69 .Fa ucp ,
  70 which must have been previously initialized by a call to
  71 .Fn getcontext ,
  72 .Xr makecontext 3 ,
  73 or by being passed as an argument to a signal handler (see
  74 .Xr sigaction 2 ) .
  75 .Pp
  76 If
  77 .Fa ucp
  78 was initialized by
  79 .Fn getcontext ,
  80 then execution continues as if the original
  81 .Fn getcontext
  82 call had just returned (again).
  83 .Pp
  84 If
  85 .Fa ucp
  86 was initialized by
  87 .Xr makecontext 3 ,
  88 execution continues with the invocation of the function specified to
  89 .Xr makecontext 3 .
  90 When that function returns,
  91 .Fa "ucp->uc_link"
  92 determines what happens next:
  93 if
  94 .Fa "ucp->uc_link"
  95 is
  96 .Dv NULL ,
  97 the process exits;
  98 otherwise,
  99 .Fn setcontext "ucp->uc_link"
 100 is implicitly invoked.
 101 .Pp
 102 If
 103 .Fa ucp
 104 was initialized by the invocation of a signal handler, execution continues
 105 at the point the thread was interrupted by the signal.
 106 .Sh RETURN VALUES
 107 If successful,
 108 .Fn getcontext
 109 returns zero and
 110 .Fn setcontext
 111 does not return; otherwise \-1 is returned.
 112 .Sh ERRORS
 113 No errors are defined for
 114 .Fn getcontext
 115 or
 116 .Fn setcontext .
 117 .Sh SEE ALSO
 118 .Xr sigaction 2 ,
 119 .Xr sigaltstack 2 ,
 120 .Xr makecontext 3 ,
 121 .Xr ucontext 3